CO-Horts Blog

Monday, June 14, 2021

Garden for Pollinators, the choice is clear! Or is it?

 Posted by John Murgel, Douglas County Extension

If you have not yet noticed, June is Colorado Pollinator Month!  National Pollinator week kicks off next Monday.  During this month and beyond, you may find yourself the recipient of a lot of different advice on how to best support pollinators in your garden.  I think all of it is given with the best of intentions; differences, sometimes strong differences, exist.  Truth be told, pollinator (and broader ecosystem) support by human activities is an area of active research and practical conclusions are difficult to draw.  To quote Dave Armstrong, professor emeritus at CU-Boulder, “Ecology is not rocket science, it’s harder.” 


Mason bee close-up
Native Bees are cuter than you think!

Here’s a conundrum perhaps not unfamiliar to many Colorado gardeners:  should I plant only natives, from local seed sources? I hear this recommendation (sometimes presented as an imperative!) frequently.  Most of my garden is a mix of non-native and “native” plants.  I put native in quotations because I have collected exactly ZERO of my plants from wild seed.  I stand by this decision—having thousands of gardeners added to the list of seed predators seems like a great way to drive wild populations of native plants to extinction.  So out the window goes “local population source” for my natives.  That will lead a conscientious gardener to the risk of genetic material from my "cultivated natives" getting into the wild populations nearby, at the risk of reducing the wild population’s fitness with “weak” domesticated genes.  At least there’s little risk of a non-native plant doing that!

 Perhaps I shouldn’t worry too much about gene flow.  After all, the “natives” I’m growing aren’t all native to my zip code, or even to my county.  Many are “Colorado natives,” or natives from the Western US, chosen more for drought tolerance than for their geopolitical pedigree.  Many true natives from undisturbed places around my home would shrivel on a day like today with the reflected heat and other challenges associated with highly modified, man-made landscapes. At least my questionable natives and non-natives have flowers to visit!

A mixed native and non-native planting
A mixed native and non-native planting

 Maybe I should plant a tree to help shade that hot landscape.  A little cooling provided by all that transpiration wouldn’t hurt either to mitigate the urban heat island effect!  Trees don’t naturally grow in my neck of the woods, so “native” goes out the window immediately.  I’ll have to water a tree, too.  But if the house is cooler naturally, the carbon-cost of cooling it with electricity on a day like today will be less.  Mitigating climate change would help pollinators, right?  What’s the “greenest” choice?  Decision paralysis seems inevitable—how to make the right choice!?

A native bumble bee visits a non-native plant
Native bee and non-native plant

 Some decisions you might make in the garden are obviously bad for pollinators—putting up butterfly houses, growing sterile, non-pollen producing plants, or liberally using insecticides come to mind.  Many other decisions, though, are good, or at least less clear.  Take the decision to plant flowers.  Should I only grow native plants for the native bees?  Plants with which they’ve co-existed for millennia?  In my garden, all the bees like all the plants—I see non-native honeybees on native plants, and native, wild bees foraging on my non-native drought adapted plants like Eremurus and Salvia.  Bumblebees really seem to like Salvia, with Echium close behind.  Should I remove the non-natives?  I have mixed feelings about honeybees, so where would that leave me?  Which suite of plants is “best”—for pollinators, for water, for climate change?  We may never know.  But don’t let the perfect get in the way of the good.  Grow some flowers, pick plants that grow where you live, and watch the invertebrates!   

Monday, June 7, 2021

June is Colorado Pollinator Month

Posted by: Jan Behler, Douglas County Colorado Master Gardener

When people hear the word “pollinators” they usually think of bees, but ants, beetles, butterflies, flies, hummingbirds, and moths are also primary pollinators in our state. Pollination is the transfer of pollen to stigma, within or between flowers and plants. A plant’s flowers need to be pollinated to complete their life cycle of producing fruit and seeds that make more plants.

Photo Credit: John Murgel
Photo Credit: John Murgel, Douglas County Horticulture Agent

Pollinators are nearly as important as sun, soil, and water in the production of most fruits and vegetables. According to the U.S. Department of Agriculture, over three-quarters of the staple crops that feed the world rely on animal pollination. On a small scale, a lack of pollination results in a fruitless tree. However, since many of the foods we eat require pollination on a larger scale that could mean a shortage to our food supply. So, the month of June has been officially designated as pollinator month to help bring awareness to the importance of pollinators.

Photo Credit: John Murgel, Douglas County Horticulture Agent

Here are a few action items to protect these important contributors to food production and beauty in our world:

  • Plant flowers in groups. Groupings or clumps of plants will attract more pollinators than single plants scattered. A bee or butterfly will feed more if they don’t have to travel too far between plants.
  • Think of providing flowers throughout the season. Plant a variety of plants that flower at different times to offer continuous pollen and nectar sources. A few examples of spring plants could include blue flax, allium, crocus, and serviceberries. For summer you might try blanket flower, bee balm, lavender, and sage.  For fall, hyssop, coreopsis, common sunflower, and golden rod.
  • Use insecticides carefully, if at all. This is self-explanatory!
  • Grow native flowering plants which are adapted to local soil and climate. Plant Select has many great plant recommendations that are suited to Colorado and known for their hardiness and low water consumption. For a good list of native plants, check out the CSU Extension Website for the fact sheets: NativeHerbaceous Perennials for Colorado Landscapes – 7.242 and CreatingPollinator Habitat – 5.616
Photo Credit: John Murgel, Douglas County Horticulture Agent

It is quite amazing but there are over 950 species of bees in Colorado alone. Did you know that hummingbirds can fly backwards and upside down? Also, t
he average lifespan of those beautiful adult butterflies is roughly three to four weeks so take a moment to look around in your yard and notice the pollinators and be kind to them this June and always!

Friday, June 4, 2021

UnBEElievable: The Benefits of Pollinators in Our World

Posted by: Lisa Mason, Arapahoe County Extension

Let’s celebrate pollinators! June is Colorado Pollinator month and June 21-27th is National Pollinator Week!

Pollinators provide so many benefits to humans and ecosystems that they deserve more recognition than just one month out of the year! Education and awareness is critical because pollinators are declining all over the world for a variety of reasons including habitat loss, pesticides, parasites, diseases, climate change, etc.

Pollinators around the world include bees, bats, flies, beetles, wasps, ants, butterflies, moths, and some species of reptiles and small mammals. Bees are among the most efficient pollinators because the pollen sticks to the hairs on a bee.

Why should we care about pollinators?

Pollinators provide valuable ecosystems services. They transfer pollen grains from one flower to another which enables the plants to reproduce. Here is a closer look at the value pollinators have to humans and ecosystems:

  • 75% of more than 240,000 plant species rely on pollinators for reproduction.
  • The global production of crops that depend on pollinators is an industry worth up to US $577 billion annually.
  • Bees help to pollinate 1/3rd of the human diet including the most nutritious part of our diet—fruits, vegetables and nuts.
  • In addition to crops, they pollinate the food for livestock that contributes to the meat and dairy industry.

In addition to providing nutritious food, pollinators offer a variety of other ecosystem services that are less known. Think of all the benefits that plants provide us. We can thank pollinators for facilitating plant reproduction for many of those plants. Examples of ecosystem services include:

  • Raw material production
  • Recreation
  • Climate regulation
  • Erosion control
  • Nutrient cycling
  • Clean air
  • Cultural value
  • Medicinal plants
  • Plant-based dyes
  • And more!

The Buzz with Bees

All bees should be celebrated! Our planet has an incredible amount of bee diversity! We have approximately 20,000 species of bees worldwide. We have over 900 species in Colorado! Most of us are familiar with the honey bee (Apis mellifera), a non-native bee species to the United States. The honey bee was brought over from Europe in the 1600’s and is a domesticated species. While they are not at risk of going extinct, they do face a variety of challenges like varroa mites. Honey bees are an important species economically and for pollinating food crops. They also provide us with honey, wax, and other products. Native bees provide an incredible amount of biodiversity and many native bees have specialist relationships with the plants they pollinate meaning other bees are unable to pollinate those specific plants. A couple of examples include squash bees that are very efficient at pollinating pumpkins and squash, and bumble bees that “buzz pollinate” plants. Buzz pollination occurs when a bee has a strong vibration frequency that allows the plant to release the pollen. Plants that need buzz pollination include tomatoes and peppers.

While writing this blog post, I took a break to water flowers in my yard. I came across this little bee who landed on my hand. This bee was less than a quarter of an inch, but she was working hard a pollinating the catmint (Nepeta spp.). She is closely related to Mason bees (Osmiini Tribe). We need a microscope to determine the exact genus, but she is likely a Hoplitis spp. or Heriades spp. bee. She has special pollen-collecting hairs on the underside of her abdomen. She is also a cavity-nesting bee.

How are you going to celebrate Colorado Pollinator Month?

Here are some ideas:

  • Observe pollinators in your backyard, parks, or open spaces. Look for visiting insects and birds that might be pollinating blooming flowers. Notice the diversity of flower visitors, and how hard they work at collecting pollen and nectar. If you take photos, you can upload them to iNaturalist, a biodiversity science database of observations. You can also explore iNaturalist to see what others are observing. 
  • Plant flowers and provide pollinator habitat in your landscape. No landscape is too small or too big. Planting some pollinator-friendly flowers or providing some habitat space will benefit the pollinators that visit. How can you provide habitat space? Keep in mind that approximately 90% of bees are solitary which means they mostly do not interact with other bees with the exception of mating.  Of the solitary bees, about 70% live underground and the other 30% are cavity nesters.  Here are some resources:
  • Join the Native Bee Watch Community Science program! All training free and provided. You can watch bees in your landscape and collect data on your observations. Register here by June 13th. Learn more about the program at Check out the CSU Source Story on Native Bee Watch.
  • Attend a virtual class during National Pollinator Week! Register here to take a one-hour class on June 25th at 12pm on who the pollinators are and how to support them. 
  • Spread the word! Check out the resources for National Pollinator Week and share with your friends, families, and neighbors. Share your photos on social media and use the hashtags: #ColoradoPollinators #PollinateCO #NativeBeeWatch #CSUExtension 

Tuesday, June 1, 2021

Be Gone, Grass (in landscape beds)!

 Posted by: Alison O'Connor, Larimer County Extension

Do you battle grass creeping into your landscape beds? Me too. And it isn't fun dealing with it. I've tried all the recommendations--pulling, mowing, digging, and herbicides. Now, before you label me as a "spray head", I'm not. I pull a lot of weeds in my landscape, mostly because I find it therapeutic. I love listening to music, filling up a bucket of weeds, and appreciating my landscape on a micro-level. However, I also have my limits, and trying to dig out bluegrass around my delicate plants isn't fun.

Kentucky bluegrass creeping in my Heuchera (coral bells).

Fortunately, the herbicides available for this problem are extremely effective and readily available. If you choose not to use herbicides, then keep on keepin' on with pulling, digging, and using mulch. These efforts can be successful, but persistence is key. Do it regularly.

If you want to consider herbicides, then look for products that contain either fluazifop or sethoxydim. There's a third, clethodim, but it tends to be more expensive. These herbicides are sold in products like Ortho Grass B Gon, Fertilome Over the Top II, Bonide Grass Beater, Monterey Grass Getter, etc.  

One of many options you can use to selectively remove grass from landscape beds.
This is not an endorsement of any particular product.

[Side note: I absolutely LOVE saying "fluazifop" and find it to be the most fun chemical name to use in everyday conversation. Flew-as-uh-fop. Fabulous.]

These are selective herbicides, meaning they will remove grass selectively from other plants. Namely, they will kill grasses, but leave your broadleaf plants unharmed. But they can injure/kill other grasses (ornamental grasses), iris, and other monocots. So read the label and use carefully.

But they do work! And usually in one application.

Use of fluazifop in my front landscape bed on bluegrass;
nearby plants included sedum and spring bulbs.

Don't worry, sedum, help is on the way!

Hang tight, little sedum, you'll be free from that bluegrass soon.

Monday, May 17, 2021

This is Colorado Noxious Weed Awareness week!


Colorado Governor Jared Polis recently designated this week, May 15-22nd, as Noxious Weed Awareness Week in Colorado. For anyone who, like me, considers themselves a Weed Warrior, this proclamation helps highlight the need for everyone in our state to take noxious weed control seriously. And while many landowners are very familiar with the identification of noxious weeds, many home gardeners are not and may inadvertently be harboring these weeds in their gardens.

As a little reminder, noxious weeds aren’t just annoyances in your yard or property: they are non-native, invasive weeds that have a competitive advantage over our vegetation and displace our native plants. Many of them are from other continents entirely and don’t have insects or disease they may have had in their native land that kept them from becoming unruly. Noxious weeds are ones that have been determined by state or local governments to be a threat to local environments and have been placed on a Noxious Weed List. In Colorado, there exist three lists of noxious weeds, and corresponding controls are needed for each.

List A species are weeds that must be eradicated whenever detected in order to protect neighboring communities and the state as a whole. These weeds may or may not be in the state yet, or may be in adjacent states and infestation is probable. Eradicating them as soon as they are found helps keep them from getting a foothold in our state.

A few plants that may be planted in gardens can be found on List A. Myrtle Spurge, Orange Hawkweed, and Purple Loosestrife are all plants that someone thought would make wonderful ornamentals in the yard, but showed quickly that they are aggressive, dominating species that quickly take over our native vegetation when they escape the confines of a garden.

Oxeye Daisies taking over fields
near Steamboat Lake

List B
species are those that are present in the state, but the Colorado Department of Agriculture, in consultation with the Colorado Noxious Weed Advisory Committee, has developed a plan to keep these weeds from spreading. Plants that were once considered ornamentals that have now found themselves on List B due to their aggressive tendencies include Common Tansy, Dalmatian Toadflax, Dames
Rocket, Oxeye Daisy, Russian Olive, and Yellow Toadflax.

List C species are weeds that the CDA will help support efforts by local county and city governments to educate people on their threat and to help use management methods to limit spread. This list includes many common ‘garden weeds,’ like Field Bindweed and Redstem Filaree. List C also includes common mullein, which is spreading along roads, railroads, and trails across the state.

Dalmatian Toadflax on a hillside

Controlling noxious weeds is not only the right thing to do if you’re a gardener or native plant advocate, but also because it is the law. Many of these weeds can be controlled with mechanical, cultural, or chemical means, and using an integrated approach to control using all of these methods is most effective. Of course, keeping the ground covered with healthy vegetation and not giving weeds a place to grow is the best solution, and also gives our native pollinators the best chance at thriving, too.

Wednesday, May 12, 2021

Underused Trees and Shrubs You Can Plant in Your Landscape

By Sherie Shaffer, Horticulture Agent, CSU Extension-Pueblo County

Planting a new tree is a great thing to do, but planting an underused tree is even better! For one, it increases the biodiversity around us. Having a variety of plant and animal species increases the overall health of an ecosystem.

Another thing to consider, is the positive effects using an underused tree would have if there were a pest outbreak. Right now, we are dealing with the potential of the Emerald Ash Borer coming to Pueblo, and many places around the state are currently dealing with EAB outbreaks. Where the EAB is present, there is a potential to lose a whole lot of Ash trees. Since Ash trees have been widely planted for decades this could cause many of our neighborhood trees to be gone. If we had a greater variety of tree species, one pest could not wipe out such a large number of trees.

If you are thinking of planting a tree, look around and don’t choose a tree species that you see already planted near your home. Here are some ideas, from CSU Extension PlantTalk scripts, for underused trees and shrubs you can plant to increase the tree biodiversity in your neighborhood:

  •         Aesculus flava (octandra) or Yellow Buckeye- Has an oval shape at maturity and can grow up to 50 feet tall. Yellow flowers appear around May. Has a great orange color in the fall. Ideally it would like a moist, well-draining soil, and it can adapt to our alkaline soils.
  •         Quercus muehlenbergii or Chinkapin Oak- Grows up to 45 feet tall and can spread just as wide if not wider. The leaves have a nice rust color in the fall. Being an oak, it will have an acorn that will mature in the first season.
  •         Pyrus calleryana ‘Whitehouse’ or Whitehouse Callery Pear- Has a columnar/pyramidal form. The leaves are glossy green, and long and narrow. Leaves turn reddish-purple earlier in the fall than other clones. The white flowers are a little later than other clones of Callery Pear.
  •         Crataegus x lavallei or Lavalle Hawthorn- It grows 15-20 feet tall and has a round to oval crown. The leaves are glossy green in spring and summer and copper red in the fall. It has white flowers that bloom in May or June and a red fruit that will last through winter.
  •         Maackia amurensis or Amur Maackia- Grows to about 20-25 feet tall and wide and has a round crown. The interesting bark peels when mature. It blooms in June and July with fragrant white flowers.
  •         Lacebark Pine Pinus bungeana- Lacebark pine has attractive exfoliating bark in patches of green and brown which makes it a good single or multi-stem specimen tree.Needles are medium to dark green about 3 inches long. It tolerates moderately alkaline soils and is hardy to zone 4 to 5.  This tree will reach a mature height of about 30, with a 15 foot width.
  •     Harvest Gold® Linden Tilia x ‘Harvest Gold’- This hybrid of littleleaf and Mongolian linden develops reliable yellow/gold fall color and is more resistant to linden aphids. As a younger tree itis less prone Harvest Gold Lindento winter sunscald than other lindens. When mature, the bark becomes mottled. You can expect this linden to reach approximately 35 feet tall and 25 feet wide. It is hardy to zones 3-4.
  •         Crimson SpireTM Oak Quercus x ‘Crimschmidt’- This hybrid of white oak and columnar English oak is a good choice where there is a need for a tall, narrow tree. Crimson Spire™ oak has attractive blue-green leaves that are resistant to powdery mildew. Leaves turn rust-red in October for 2 weeks. The leaves then turn brown and persist into early spring. Hardy to Zone 5, you can expect this oak to reach 35 to 40 feet tall and 12 to 15 feet wide.  It has shown some intolerance to wet soils.

In addition to these great underused trees, native species are always a wise choice. You can find a list of Colorado native trees here:  , and a list of native shrubs here:


Monday, May 10, 2021

Aspen Alternatives for the Front Range

By Amy Lentz, Weld County Extension Horticulture Agent

It's tree planting season which means there are choices to be made in yards all across the state. But which tree should you choose?

Today's tree-in-question - the aspen. So many of us want one in our yard to give us that 'Colorado' feeling. From the beautiful white bark to the perfectly shaped and uniform green leaves, or maybe it's the fall color or rustling sound that you just have to have! Before you go out and buy an aspen to plant in your home landscape, I urge you to reconsider if you live along the Front Range or Eastern Plains. These native trees are only native to the higher elevations of Colorado, the mountains and foothills.

Aspen fall color in mountains

Aspens have a few needs that just can't be met down at lower elevations. For one, the soil is much different than that of the higher elevations - it's higher in clay content, more alkaline and drier. The temperatures get much hotter in the summer at lower elevations than what the aspens prefer which can lead to stress. Once an aspen tree is stressed, it can invite other insect and disease problems like oyster shell scale, Marssonina leaf spot or cytospora canker. See PlantTalk Colorado - Aspen Trees (#1701) for more information.

Finally, aspens want to reproduce via suckers and create groves and many home landscapes are just not big enough to accommodate a grove of aspen trees. If you plant an aspen in a small yard, you've probably just planted an aspen for all of your neighbors, too!

Photo: Amy Lentz - Aspen trees in Rocky Mountain National Park. 

So, instead of choosing an aspen tree for your Front Range yard, here are a few interesting alternatives. They won't be exactly the same, but they have similar qualities with much less caution required. 

1. Serviceberry

Serviceberry trees are great for smaller landscapes. They can be purchased in multi-stem form, giving them that 'grove' look without the suckering. They also offer a few things that aspens don't - spring flowers, summer edible fruits and nice fall color. The 'Standing Ovation' cultivar is a taller form, giving it more of that aspen look, whereas the 'Autumn Brilliance' has an intense orange-red fall color.

Photo: PlantTalk Colorado 1213 - Serviceberry

2. Tatarian Maple

Tatarian maple is another tree that can be bought as single or multi-stemmed. The 'Hot Wings' type has guaranteed bright-red summer seed pods creating the appearance of flowering. This tree is better suited to the harsher conditions and low-water or xeric settings once established.

Photo: Adams County Extension Tour the Xeric Garden @ Riverdale Regional Park

3. Redbud

If you like the smooth bark of the aspen, the redbud has a similar appearance in its younger bark but with a more grayish tone. The leaves are larger, but also have that similar heart shape. The redbud also offers a nice display of early spring lavender blooms in most years. Plant this tree in a more protected location from wind and intense sunlight.

Photo: Amy Lentz, taken outside the Boulder County Clerk & Recorder Offices in a very protected northeast facing corner

4. Oakleaf Mountain Ash

If you want something 'mountainy', the oakleaf mountain ash has 'mountain' in it's name! It has low to moderate water needs and has a uniquely shaped leaf, pretty flowers, red berries and nice orange-red fall color. It's not a true ash, so it is not under threat by the Emerald Ash Borer. In fact, it is not known to have any serious insect or disease issues. 

Photo: City of Sheridan, WY - Arboretum

5. Columnar and Fastigiate Trees

So many to choose from! These types of trees are more narrow than wide, making them good for tighter spaces where you might commonly want to plant aspen trees. There are a lot of deciduous trees listed on our CSU Fact Sheet. A couple to consider might be the 'Princeton Sentry' ginkgo or the 'Prairie Sentinel' hackberry. 

Photo: Wikimedia Commons - 'Princeton Sentry' ginkgo

Thursday, May 6, 2021

Climate change and pollinators

 By Irene Shonle, CSU Extension El Paso County

Plants and pollinators have evolved over the millennia to depend on each other. Pollinators need the nectar and pollen that plants provide, and plants need the pollinators to carry pollen from one plant to another to achieve fertilization and seed set. 

Climate change is having a negative impact on both plants and pollinators as the changing temperatures affect each species differently. In some cases the resulting mismatch in bloom time and pollinator activity can mean that some plants don’t get pollinated, and some bees don’t find the food they need at a critical time.

Plants tend to bloom primarily in response to a combination of increasing temperatures and daylight. This is why we see flowers bloom earlier in years with warm springs, and later in cold springs.  Insects also respond to similar environmental cues, which makes sense, given that mutually dependent species would be expected to be fairly synchronized.

European scientists Holzschuh and Kehrberger found that the European pasque flower (Pulsatilla vulgaris) responds to rising temperatures by flowering earlier each year, whereas one of its major pollinators, a solitary bee species, does not quite keep pace by hatching earlier. 

This system may have worked well for ordinary weather vagaries, but the warming of the earth’s climate has caused plant species to bloom an average of a half-day earlier each year. In total, that can result in the growing season of some species now beginning up to a month earlier compared to 45 years ago. Insects aren’t quite keeping pace, although the timing of their emergence is less well understood than with plants, especially for solitary, ground-nesting bees species (as many in Colorado are).  It appears as though insects have a higher threshold temperature for development than those required for plants, so plants are more likely than insects to bloom earlier in response to springtime warming (Forrest and Thomson, Ecological Monographs 2011, Holsuch and Kehrberger, Plos 1 2019).

This has implications for both wild populations of both the plants and pollinators.  If pollination gets missed, early spring ephemeral plants (which are often critical early nectar plants) will reduce in population size. Pollinators that miss the peak bloom of an important plant will be forced to switch to a different species – if another one is even availableavailable (Holzschuh and Kehrberger Plos One 2019).

Wild plums provide early nectar for pollinators

On a home landscape level, we can all help the pollinators by
including a variety of flowering plants that bloom from the very earliest days of spring until later in the season when more is in bloom.  Walk around your neighborhood and open space to see what is blooming when, and take notes, especially of plants that you don’t already have in your yard- such as perhaps quince, currants, plums, creeping phlox or violets.  Highly hybridized plants like tulips and daffodils may or may not provide nectar, despite their showy flowers.

Three lobed sumacs (Rhus trilobata) don't have showy flowers, but are great for early pollinators

There are some early plants that aren’t as showy, but still provide nectar and pollen – such as maples, sumacs and even willows.  If an early spring means the pollinators miss one plant, a diversity of plants with slightly different bloom times will mean that the insects can still find food.

We can all do our part to keep pollinator populations as robust as possible – starting with our own backyards!

Monday, May 3, 2021

Debunking the Myths of Soil Amendments

Posted by: Robert Sanchez, Douglas County Colorado Master Gardener

As we get the outdoor itch from being cooped up all winter as a result of from the pandemic and cold weather, some of us think about going to the local nursery to purchase compost, peat moss, manure, and other soil amendments to get ready for gardening. These are all important elements of gardening but amending the soil has so many misconceptions I thought I would address a few. First, let’s look at the science.

The ideal soil consists of about 25 percent air, 25 percent water, about 45 to 47 percent mineral matter, and about 3 to 5 percent organic matter. Soil texture and soil structure are also important elements. Soil texture refers to the size of particles that make up the soil, including large particles of coarse sand, medium particles of silt, and small particles of fine clay. The larger the particle, the more space for air, but too many large particles allow water to drain away. Thus, coarse sand by itself is not a good growing medium for roots. Scientists refer to the ability of roots to grow in soil as soil tilth. Soil structure refers to how the various particles of sand, silt, and clay fit together. A good soil has a mixture of various sized particles with various chemical and biological components that bind the particles into aggregates. An ideal soil allows air for microbial activity and root growth and retains water. Organic matter in the soil does increase water-holding capacity in the soil.

Now let’s explore a few myths about soil amendments.

Myth #1: Amending the soil will change the nature of the soil. We have notoriously clayey and alkaline (high pH) soil in the Front Range. Adding compost to the soil will not change the nature of the soil. Changing the nature of the soil requires either changing a little bit of the soil over a period of years, such as what nature does on a geologic time scale, or replacing the soil entirely in one fell swoop. The home gardener can speed up the geologic time scale by making changes faster than nature would do, but changes to the nature of the soil would still require years. We can see what it takes to change the nature of the soil by observing new building construction. Typically, construction crews excavate several feet of soil to install utilities and the building infrastructure, removing the top layer of soil that contains most of the dead and living organic matter. As the crews replace the soil to continue with construction, the organic matter is no longer near the surface, living matter has been destroyed, construction debris (gypsum, sand, concrete, and wood) has been added, and crews have pulverized the soil, snuffing out what little life or air that might have survived the onslaught. This process illustrates what it takes to change the nature of the soil. Even adding a lot of compost to a hole when planting does not change the nature of the soil, except for the soil you replaced in the hole, and that is only temporary because the organic matter in the compost will decompose, leaving only the natural soil and decomposed remnants.

Myth #2: Adding lots of compost during planting promotes root growth and plant health. Adding organic matter when planting does indeed promote root growth, but it may not result in a healthier plant. The ideal soil only contains 3 to 5 percent organic matter and filling a hole with 25 percent organic matter (or more) when planting is not ideal. Under good watering and sunlight conditions, the initial results of all that compost appear good. That is, roots show vigorous growth and the canopy of the plant responds accordingly. Then the roots hit the edge of the hole and encounter natural soil with less compost in it. Preferring the compost to the natural soil, the roots circle back into the compost, resulting in a condition called “girdling” roots. The result is an unhealthy lack of spread of the roots into the natural soil. When the compost you initially placed in the hole decomposes, the roots will actually have less access to nutrients because they have not extended their reach beyond the now decomposed compost to absorb more nutrients. In addition, the different soil textures inhibit the natural flow of water, so water falling on one soil texture may not flow into soil with a different texture, leaving some soil dry. Specifically, water cohesion allows water to coat soil and mineral particles, which is one reason organic matter retains water so well. Water moves through fine clay soil through capillary action. Thus, water does not readily move from organic material to clay or from clay to organic material because of the different processes facilitating water movement. Different soil textures do not promote root growth.

Myth #3: Enough application of compost will solve most soil problems. If a planted plant dies, an incorrect assumption is that it did not have enough organic matter. Organic matter is a necessary element for root development and plant health, but it cannot solve all soil problems. Drainage, compaction, sunlight, microclimates, and salt buildup are all problems with soils that organic matter might not necessarily help your plant overcome. In fact, adding too much organic matter, particularly manures, could increase salt buildup in the soil. Soil amendments can be deceptive because in the short term, the added benefits can be seen in the growth of the above-ground portion and overall apparent vigor of the plant, but over the long term, the detriments could outweigh the benefits. Applying organic matter is one aspect of gardening. However, managing other cultural practices, such as planting the right plant in the right place for the drainage, soil conditions, and sunlight, is no less important.

The takeaway from all this is to understand the holistic needs of plants in your garden. Amending the soil is one important part of the holistic view but understanding what it does and does not do can help you attend to your plants much better. For more information on soil amendments, see

Thursday, April 29, 2021

Help Fight Hunger in Your Community

 By Carol O'Meara, Boulder County Extension

  Lingering impacts from a disrupted world are hitting our community, with hunger a growing problem. Last year, gardeners responded to the crisis by reviving the Victory Garden movement, growing and donating over 23 tons of produce to food banks and pantries across Colorado through the Grow & Give project.

Victory Gardens have been cultivated throughout our history as a country, popping up when events take a toll on our collective wellbeing. During economic crashes, depression, and war, people sow, grow, and share. As spring warms the soil and the itch to plant consumes us, gardeners are being asked to plant extra to help combat a rise in hunger. The numbers from this aspect of our shared catastrophe are grim.

Hunger Free Colorado  conducted quarterly surveys in 2020, mapping the increase in hunger due to heightened effects from the pandemic. Their third statewide survey, conducted in December, found almost 38-percent of Coloradans are food insecure, lacking reliable access to nutritious food. This is more than two times what Colorado experienced during the Great Recession.

The survey found that more than half of households with children are struggling to have regular access to nutritious food, while 19-percent of children are not getting adequate nutrition because there is not enough money for food.  Twenty-five-percent of adults reported having to cut back or skip meals because there wasn’t enough money to buy food.

Gardeners, we give advice, seeds, and plant divisions freely to anyone who’ll take them.  We joke about too many zucchini or the year cherry tomatoes buried us.  Let’s plan for that bounty this year in order for others to eat, and plant an extra hill or two of zucchini or pop another cherry tomato vine in the ground. Let’s sow for our community as well as ourselves.  

Want to grow food but need a bit of advice? Check out the new Grow & Give website to find short how-to videos, longer webinars, or information sheets on growing fruits and vegetables in your garden. You’ll find information added weekly, but if there’s a topic you’d like to see covered, send me an email with your suggestion.

Sign the pledge to donate part of your harvest and join a community of concerned gardeners who want to make a difference. The website has a map of food pantries and locations for drop off, along with information on days and times they’re accepting donations.

You can help. Plant extra and donate it to pantries, to your neighbors who need it, or friends who have seen a decrease in income. Whether it’s a dozen carrots or a hundred tomatoes, it doesn’t matter. Grow, and give.

Monday, April 26, 2021

A Wasp-Benefit Analysis – Part II: Social Wasps

Posted by: Lisa Mason, Arapahoe County Extension

In case you missed it, click here to read Part 1. We covered the purpose of wasps in the ecosystem and answered questions on the Asian giant hornet that made headlines in 2020. Part II will cover social wasps, their role in the ecosystem, and possible control methods if they become a nuisance.

Wasps sometimes get a bad reputation because they can sting and are sometimes a nuisance. We have one species of wasp that can be particularly aggressive: the western yellowjacket. Don’t let one or two species of nuisance wasps ruin your opinion of all wasps. Wasps are a diverse group of insects that provide important ecosystem services such as pest control.

Social Wasps

Social wasps are probably the most familiar wasps to people because they are easily seen in the yard and landscape. Social wasps live in a colony together. They have a similar lifecycle to a bumble bee (Bombus spp.).  A new colony is started each year by a fertilized queen that survived the winter. She will lay several generations of female workers throughout the season. Towards the mid-to-end of the summer, she will lay eggs that are male wasps and potential queens. The males and potential queens will leave the colony to find a mate. Once cold temperatures arrive, the current colony will die except for the newly mated queens. The cycle will repeat and the following spring, when the new queens begin a new colony. Social wasps always build a new colony each year. They never reuse old nests, which is important to note if you’re looking to control nuisance wasps. Social wasps make their nests out of chewed up wood, creating a paper nest. Social wasps also feed on insects like caterpillars, providing important pest control in our backyards. The western yellowjacket is a scavenger feeding on carrion and human sources of food such as trash.

Let’s discuss five species of social wasps that are found in Colorado. Understanding the life history of social wasps can help you control them if they become a nuisance in your landscape, and build appreciation for their complex social biology, along with the pest control services they provide.

A western yellowjacket. Photo: Lisa Mason

Western Yellowjackets

Western yellowjackets (Vespula pensylvanica) are a native, social wasp that you will find at your family BBQ, picnics, trash cans, etc. They are very common in urban landscapes and can become a nuisance. Like social wasps, they create a new colony each year. The paper comb nest is usually underground or in a cavity that is well-protected. While yellowjackets are commonly seen, their nesting site can be difficult to find.

Yellowjackets can be aggressive, especially when defending their nest and are responsible for 90% of the insect stings in Colorado. They are scavenging insects feeding on carrion, dead earthworms, garbage, human foods including meats, and sweet, sugary foods. They also will feed on honeydew, a sweet substance excreted by aphids and soft scale insects.  Scavengers are the clean-up crew for ecosystems and play an important role in the food web. Yellowjackets tend to get more aggressive in the fall as food can be harder to find. 

If yellowjackets tend to be a nuisance in your landscape, you can purchase a yellowjacket trap available at hardware and garden stores. The traps contain heptyl butyrate which yellowjackets are attracted to. Traps will be most effective if they are placed outdoors in the early spring to capture the overwintering queens before they start their new colonies. Nest removal can be a dangerous task and difficult because their nests are so well-protected. Insecticide treatments often aren’t effective because it is difficult to get the insecticides inside the colony. Hiring a professional is often necessary. Remember, the colony will only last for one season.

An underground entrance to a western yellowjacket nest. Photo: Nancy Bonita

European Paper Wasps

European paper wasps (Polistes dominula) are much less aggressive, but they often build their nests close to human activity. They are a non-native insect that has become well-established in Colorado. They first appeared in Colorado in the late 1990s/early 2000s. They prey on caterpillars and other insects and feed their young live insects. Common prey includes hornworms and cabbageworms. They also will feed on honeydew secreted from aphids. The papery comb nests are often found under house eaves, overhangs, sheds, pipes, and other hollow spaces in human infrastructure. 

If the paper wasp nest is located in an area that won’t be disturbed by people, the nest can be left alone, and the wasps likely won’t be a nuisance. The current colony won’t survive when temperatures cool in the fall. If the nest is close to human activity, there are insecticide treatments to destroy the nest. Following instructions on the insecticide label is critical. Insecticides should be applied at night when most wasps are present at the nest. The nest should be destroyed afterwards to also kill the capped larvae in the nest. The location of the nest site should be thoroughly washed to prevent any remaining wasps from building a new nest. 

Traps that attract yellowjackets will not attract paper wasps. There are no effective trap methods for paper wasps.

A European paper wasp. Photo: Lisa Mason

Baldfaced Hornets and Aerial Yellowjackets

Baldfaced hornets (Dolichovespula maculata) and aerial yellowjackets (Dolichovespula arenaria) are common in Colorado but are less likely to be a nuisance around human activity. They are only aggressive when their nest is threatened. They develop a large papery comb nest usually high in large trees and shrubs. They feed on caterpillars, other insects, and honey dew. If you find a nest in your tree or shrub, it may look intimidating, but the nest can likely be left alone if the nest can be left undisturbed. These two wasps can be common visitors in our landscapes but often go unnoticed by people.

A baldfaced hornet. Photo: Joe Boggs, Ohio Sate University Extension

A baldfaced hornet nest. Photo: Joe Boggs, Ohio Sate University Extension

Western Paper Wasp

The western paper wasp (Mischocyttarus flavitarsis) is a native paper wasp in Colorado and the western US. They have a similar biology to the European paper wasp. They are capable of building paper nests close to human infrastructure and activity, but they are not nearly as common as the non-native European paper wasp. They can sting if their nest is threatened, they often prefer to “ram” into the person or animal that is threatening the nest (Snelling, 1953). Like other paper wasps, they prey on caterpillars, flies, and other pests, bring the prey back to the nest to feed the young wasps the live insects. Adult wasps may also forage for nectar on flowers.

A western paper wasp visiting my cup of tea earlier in April. Photo: Lisa Mason

A Note About Insect Stings

Western yellowjackets are responsible for 90%+ of all stings in Colorado. When someone says, “I was stung by a bee,” they were likely stung a yellow jacket.

Both bees and wasps can sting. A stinger is a modified ovipositor (the egg-laying mechanism in insects), so only females have the ability to sting. The purpose of a stinger is defense, and in some species, predation. Generally, insects will only sting if they are provoked or their colony is disturbed.  Both social and solitary wasps and bees can have the ability to sting, but social insects are more likely to sting because they need to protect their colony.


Honey bees prefer to forage on flowers and go about their business in their hive, but they can sting if they need to protect their hive. Honey bees can sting only once. They have a barb at the end at the end of their stinger that stays in your skin. The barb is attached to the internal guts of the bee, so when the bee tries to fly away, the guts are ripped out of the bee’s body, which kills the bee.

Bumble bees have the ability to sting but will only sting if their colony is disturbed. They can also sting more than once unlike honey bees. Bumble bees are not aggressive and prefer to forage on flowers and go about their business. Many native bees are not able to sting or will only sting if handled.


Wasps can sting more than once. Solitary wasps will only sting if they are pressed up against your skin, or you try hard to provoke them. They prefer to fly away and stay away from human activity. Social wasps can be very defensive if their nest is disturbed. They also can sting if they are away from their nest and provoked. The western yellowjacket is much more likely to sting because they are scavengers and attracted to human foods sources. They tend to get more aggressive in the fall when temperatures cool down and food is harder to find. Other social wasps including the European paper wasp are generally not aggressive unless their nest is disturbed. The European paper wasp tends to build nests close to human activity on buildings, sheds, and other structures, which can increase the chance of nest disturbance.

Learn More

Western yellowjackets and European paper wasps can be a nuisance to people and often attract attention, but these wasps and other social wasps represent a small part of wasp diversity. Look for a future post on the CO-Horts Blog about solitary hunting wasps. These wasps often go unnoticed in the landscape, but provide valuable pest control services! 

Monday, April 12, 2021

Protecting your plants from wild weather this spring

Posted by: John Stolzle, Jefferson County Extension
Spring weather in Colorado can be temperamental, it can sometimes feel like we experience all of the seasons in a single day. This past weekend, if your garden was located around the Front Range, it likely experienced warm springtime weather ripe for growing; but later this week, forecasts predict cooler temperatures and even a possibility for snow! These erratic fluctuations provide challenges for our gardens, but CSU Extension has put together some techniques which can help gardeners to extend the growing season and to protect plants against some these drastic weather patterns.
In this post, I have highlighted some techniques and provided references with more information for managing your garden with our spring weather in mind.
Seedlings purchased from a garden nursery may need to be hardened off before they are planted in your garden [click here for more information on this topic]. 

One of the most important factors to consider in vegetable gardening is when to plant your garden, and the length of your garden’s growing season. If planted too early, some vegetables can encounter challenges with frosts which can kill tender plants; but if planted too late, crops may not mature by the time fall comes around. By planting the right plants at the right time you can help to cultivate a successful crop.
Planting Guides can help you decide
when to plant certain things.

Cool, hardy season crops can often tolerate minor frosts and thrive in cooler weather conditions which dip as low at 40°F, some examples are broccoli, spinach, and onions. Warm season crop are much more sensitive to frost and should not be planted until all danger of frost has past. These plants do better in temperatures ranging from 70°F - 95°F, some examples are tomatoes, peppers, and watermelon. A longer list for these plants, and more details on this topic can be found in the following link to CSU Extension's vegetable planting Guide:
There are a range of techniques which can be used to extend our growing season. These include things such as planting gardens on south-facing slopes, providing windbreaks, mulching, and even covering plants when frosts are suspected. Sheets and blankets can be used to trap heat from the soil around young vegetables at night; these covering should be placed low to the ground and secured. In the morning after using sheets, if this fabric has become damp it should be dried before being used for this purpose again.

Simple hoops over a garden can provide great
fastening points for hail cloth and shade cloth.

More techniques and helpful tricks to extend the growing season can be found in the following link to a factsheet on this topic:

Frosts and cold snaps are one challenge, but hail can be one of the greatest risks to our gardens.  Hoop houses or high tunnels can both extend the growing season and offer protection from hail. Hoops can also provide structures to which tightly woven ‘hail cloth’ can be fastened for added protection; hail cloth can also be placed over tomato cages or other structures available in your garden.

Walls of water and gallon milk cartons (with the bottoms cut off) can be used to protect new seedlings. If you leave the cap off of these cartons, they can even be left over seedlings until the plant outgrows this structure. Your imagination is the limit! Before a hailstorm, cardboard boxes, plastic buckets, and even sheets can help prevent some of the most extreme damage from occurring; however, you should never risk personal safety to protect your garden and should only implement these methods if you are able to get out far enough ahead of a storm for it to be safe.

A seven minute video on Hail Mitigation and cleanup can be found in the following link to more information provided by CSU Extension staff:

A factsheet on this topic can be found on the following link:

Sometimes it isn't possible to protect our gardens from a rapidly developing hailstorm. If you don’t find yourself with enough notice that a potential storm is coming or perhaps find yourself away from your garden when this weather occurs, you should know that our plants can recover! They want to grow.  To include a direct quote from our Plant Talk page on this topic:

For perennials with foliage intact but stripped, remove flower stalks and cut them back leaving as many intact leaves as possible. Lightly cultivate the soil, and apply a light dressing of low-nitrogen fertilizer.­  

Flowering annuals with no remaining foliage probably won’t recover after a hailstorm. Petunias usually survive if there is at least some foliage still on the plant. Clean the plants of ruined foliage and apply a light application of fertilizer to help them recover.  

Early vegetable root crops with no remaining foliage will not recover. They need the green leafy foliage to produce energy for the roots to grow. Leafy vegetable crops may recover; replant if you see no signs of new growth after a week or so.


The reality is that Colorado's climate and weather patterns are challenging for gardens. But, CSU Extension is here with specialized knowledge to help you grow successful gardens of abundance. To get started, check out the following two links to the Colorado Vegetable Guide: 

en EspaƱol

and In English

For a wealth of information on gardening, I would also highly encourage you to check out our 'Growing' resources at