CO-Horts Blog

Monday, July 13, 2020

Garden Problem Tour

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

   This summer, COVID-19 has the Extension office in Pueblo closed down, so I have been working from home. This has given me a chance to look around at things going on in my yard and garden that I haven’t had time to pay attention to in previous years. Of course there is a lot going right, but here is a little tour of the issues I have found this year. Maybe you have some of the same issues, and I can offer some suggestions on what you can do to remedy them.
   I have several trees in my yard that were here when I moved in. While doing some much needed trimming earlier this year, I noticed one of my American Elms had a very black trunk and branches. Upon further inspection, I noticed small brown and white structures in the cracks of the bark that looked similar to mealy bugs. What I have is a pretty bad case of European Elm Scale. The black color on the trunk and branches is black mold and is commonly associated with scale infections. There aren’t many control mechanisms that work well, but if you have Elm Scale you can see your options here: For me, this tree is not in a great place and runs into my power lines so I won’t be sad to lose it and therefore probably won’t treat it. If my neighbors or myself had other American Elms it could spread to this might be more of an issue.
   The next problem I saw in my yard was in my lawn. It looked really great earlier in the year, but with the extremely hot weather we have been seeing in Pueblo I’ve been seeing some brown spots appearing. There are many potential causes of brown spots in lawns, but by far the most common cause is a lack of water due to poor irrigation coverage. I’m sure this is the problem that I am seeing, but to be sure I will be performing a simple at home lawn irrigation audit. To do this, set out identical containers in different spots in your lawn (brown spots and green spots) and run your system. You can measure the amount of water in each container to see if the brown spots are getting less water. To read more about brown spots in lawns click here:,to%20maintain%20a%20healthy%20lawn.
   Next, I checked out my vegetable garden and noticed my zucchini plant had leaves that looked white and powdery. This is a common fungus you might see on cucurbits, called powdery mildew. It’s caused most often by poor air circulation and too much shade. Shade is definitely my problem. Neem and horticultural oils can be used on existing infections, but can damage plants if used improperly so always read the label and check out this link for extra information: I’ve made my first application of Neem oil and am hoping for good results.
   Also in my vegetable garden, I noticed some of the tomatoes were getting cracks and indentions. This can be caused by inconsistent watering. The plants get a bit dry, and then suddenly get a bunch of water, and the fruit basically outgrows its skin and cracks. I think I will try to be better about the watering schedule, and also add some grass clippings or straw as mulch to stabilize the soil moisture. I know a lot of people have various problems with tomatoes. This fact sheet is amazing for narrowing down the problem:
   So that’s a tour through the yard and garden issues I am having. I hope someone will see one of my shortcomings and be helped by it!

Tuesday, July 7, 2020

Cole Crops for Fall Harvest

Posted by Sarah Schweig, Broomfield County Extension

I grew kohlrabi in my home garden for the first time this spring. I opted for a purple variety, though more common varieties are light green to white. The plants were beautiful, tasty, and front runners for the Least Fussy Award. A spot of good luck? Perhaps, but this was a feat for a spring crop for reasons I'll describe below. My overwhelming feeling was “Why didn’t I start growing these earlier?” I'll be seeding for a fall crop soon, and if you haven't grown kohlrabi yet, you can still give it a try this season.
White and Purple Kohlrabi (Photo: University of Kentucky)
The name kohlrabi comes from German and translates to “cabbage turnip.” Turnip and kohlrabi are both Brassicas. Rather than the edible taproot of turnip (Brassica rapa), the prize of the kohlrabi plant (Brassica oleracae) is the stem, which enlarges at maturity, forming a turnip-like bulb just above ground. Kohlrabi has a more mild flavor than turnip and is ever so slightly sweet, but they’re prepared in the same way.

Kohlrabi is more closely related to - in fact, the same species as - heading cabbage, broccoli, cauliflower, brussels, and kale, collectively referred to as cole crops. Whereas turnips and kohlrabi will provide you with a similar experience once prepared, I have always loved thinking about the totally different experiences modern Brassica oleracae varieties offer. My favorite description of the species is having a “remarkable natural tendency for thickening of plant parts,” and it provides the perfect visual for their domestication and divergence from the same wild cabbage plant.

Photo from University of Nebraska
Kohlrabi was bred by selecting for thicker stems; cauliflower through selecting for thicker immature florets; broccoli was selected for thicker florets and floral stems. While selecting for a thick terminal bud gave us cabbage, selecting for many enlarged axillary buds (the "sprouts") gave us brussels.

I’m glad I successfully dipped my toe in growing kohlrabi this spring, but I’m partial to growing cole crops for a fall harvest for a few reasons. First, it’s easier to direct seed. Cole crops like soil temperatures around 80ºF for germination, but they can bolt or become overly tough or bitter if temperatures are too warm, especially around heading. Combined with relatively long time to maturity, it’s a challenge to get the timing right when starting these plants from seed in the spring.

Pest pressure can also be eased in planting for a fall harvest. I tend to have issues with flea beetles. Most flea beetle damage is caused by adults, which chew characteristic “shot holes” on the interior of leaves. While plants can withstand quite a bit of this type of injury once established, flea beetles can be tough on younger plants. In my fall crop, I get to avoid their most active time in vegetable gardens (late May and early June in my area).

With early kohlrabi varieties maturing in as little as 40 days, and most common varieties maturing in around 60, July to August is a good time to seed your fall crop for a harvest in September, depending on your location. They can withstand some frost, and bonus, you can get bigger, sweeter harvests with a fall crop. Kohlrabi is usually harvested when the bulbous stem is 2-3” wide. After this point, the stem can become woody in higher temperatures, but cooler temperatures in the fall will keep them more tender longer.

Like familiar Brassicas, kohlrabi is a heavy nitrogen feeder and requires ample moisture and space to develop properly. Use an organic mulch to help regulate moisture and soil temperature. Most varieties require a minimum of 12” spacing, but always check your seed packet for specific information. Planting too close together may result in elongating of the stems rather than the thickening you want to see. Harvest the whole plant (I’m a big fan of the greens) by cutting just above the soil surface. Kohlrabi can be stored for months in cold, moist conditions (around 36ºF and 95% humidity), but most of us can’t create these conditions at home. Kohlrabi will last a couple of weeks after harvest in your refrigerator. 

For more information on cole crops and other ideas for your fall vegetable garden, check out the new Colorado Vegetable Guide.

Thursday, July 2, 2020

The Fascinating Lives of Butterflies

Posted by: Lisa Mason, Arapahoe County Extension

One of my favorite parts about summer is watching butterflies. We have quite a variety of species in Colorado—over 250 according to What is so fascinating about butterflies? For me, one aspect is the process of metamorphosis. Many insects go through a full metamorphosis, but butterflies and moths can have such striking colors and patterns on the caterpillars, cocoons and chrysalises, and the adults.

I recently had a client contact the Extension office about caterpillars feeding on pansy plants. When I saw pictures, I knew they were the variegated fritillary caterpillars (Euptoieta Claudia)! Since the voracious caterpillars were causing quite a bit of damage to the pansies, he was looking to remove them. I immediately agreed to take them! I took photos at various stages of their life so I could share the wonderment with you. See the pictures at the bottom of this post.

The viceroy butterfly (Limenitis archippus) closely mimics the monarch. Photo: Lisa Mason 

Butterfly and Moth Basics

Some facts—butterflies and moths:
  • Are part of the insect order Lepidoptera meaning scale wing
  • Are characterized by two characteristics: 1) their wings are covered in scales which are modified hairs, and 2) they have a proboscis which is a long, tubular mouthpart.
  • Go through a full metamorphosis consisting of four life stages: an egg, larva, pupa and adult
  • Have slight variations in each individual—just like a snowflake, no two individuals are the same, but the differences are very hard to spot in the outdoors
You can distinguish a butterfly from a moth a few different ways. Butterflies are diurnal, active during the day, while moths are generally nocturnal, active a night. Butterflies also tend to be more colorful which helps them attract a mate. Moths attract mates through smell. Their dulled colors help them camouflage at night to avoid predators. In addition, butterflies generally have antennae that are clubbed-shaped versus moth antennae usually taper to a point, or look feathery. Male moths in particular have large, feathery antennae. Moths also appear “fuzzier” than butterflies because the scales on their body are much thicker to keep them warm since they are mostly active at night. Butterflies rely on the sun to keep them warm. Both position their wings differently. Butterflies tend to fold their wings together, and moths hold their wings out to look more like a tent-shape.

Migration Phenomenon

One of the most fascinating things about butterflies is the migratory patterns of some species. Two migratory species of note that occur in Colorado are the monarch and the painted lady.

Monarch butterflies (Danaus plexippus) host on milkweed plants (Asclepias spp.) which contain a milky compound that is toxic to predators such as birds. The bright colors on monarch butterflies is often a warning to predators about the toxicity.  The migratory corridor of monarchs is through the Midwestern US as far north as Canada, and as far south as Mexico. Monarchs also migrate up the west coast of the US.  Colorado is not directly on the migratory path of monarchs, but we do see them here. Monarch butterflies use the position of the sun to navigate and a magnetic compass to orient when the days are cloudy. They possibly use a combination of both regularly. More research is needed to fully understand how monarchs navigate for the migration. More information here.
Adult monarch butterfly. Photo: Lisa Mason

Monarch butterfly caterpillar feeding on milkweed. Photo: Lisa Mason
Painted lady butterflies (Vanessa cardui) are a common butterfly seen in Colorado. You may remember in 2017 when we had an explosion of painted lady butterflies in the fall! Painted lady butterflies are also a migratory species. They overwinter in the southwestern US and in Mexico. They migrate northward in the spring as plants become available. The population numbers in Colorado and surrounding areas depend on the weather in the southwestern US. When the southwest has more precipitation, the butterfly population will increase. All those butterflies then migrate northward. When the southwest has years of less precipitation, you might not see many butterflies. Painted lady butterflies are generalists and will forage on a variety of nectar-producing flowers. The caterpillars host on thistle, hollyhock and sunflowers. More information here.

Painted lady butterfly. Photo: Lisa Mason
A Few Other Species in Colorado

Two-tailed swallowtail butterflies (Papilio multicaudatus) are large (up to 5 inches long), yellow and are a commonly seen butterfly along the Front Range. The caterpillars feed on green ash and chokecherries. With the emerald ash borer growing along the Front Range, two-tailed swallowtails will many lose many ash trees as potential host sites. What can you do? Plant chokecherry trees! If you treat your ash tree to protect it from EAB, likely trunk injections would be a safer treatment method for these butter flies rather than trunk sprays.  The adults feed on nectar from thistles, milkweed, and other flowers. Two-tailed swallowtails can be differentiated from tiger swallowtails by a second projection off their hindwing. More information here.

Two-tailed swallowtail adult. Photo: Lisa Mason

Two-tailed swallowtail caterpillar. Photo: Lisa Mason
Black swallowtail butterflies (Papilio polyxenes) had a great year in 2019. They were very common in gardens along the Front Range. The butterflies are large and mostly black with some yellow markings. They host on plants in the carrot family (Apiacaea) including dill, parsley, and fennel. When the caterpillars are small, their colors resemble bird droppings that can help them camouflage. As the caterpillars grow, their colors become more striking with green, black and orange markings. More information here.

Colorado hairstreak butterflies (Hypaurotis crysalus) is the Colorado state butterfly! Haven’t seen this butterfly? You are not alone. They tend to be fast fliers. These butterflies host on gambel oak, which is a common shrub in the Colorado foothills and mountains. They don’t stray too far from their host plants, even as adults. You likely won’t catch these butterflies on flowers either. They tend to feed on sap from the trees, and honeydew from aphids and other insects. Some years have higher populations than others, likely dependent on the weather. More information here.

Common buckeye butterflies (Junonia coenia) aren’t the most common butterfly you see in Colorado, so if you do see them, take note! These lovely butterflies overwinter in the south where is warmer. Adults will migrate north to places like Colorado and will colonize over the summer months. The adults prefer flowers in the Asteraceae family including aster, gumweed, and tickseed flowers. Caterpillars host on snapdragons, toadflax and plantains. More information here.

Common buckeye butterfly. Photo: Lisa Mason
Attracting Butterflies

To attract butterflies to your backyard this summer, provide the following:
  • Nectar plants that are brightly colored and have a landing pad for the adults
  • Caterpillar host plants
  • Sunny, open areas
  • Trees and shrubs to protect them from wind and weather
  • A water source such as a shallow dish
For more information, visit Attracting Butterflies to Your Garden. Visit for details on what species have been documented in your area. You can find a lot of great field guides on butterflies. I recommend the Field Guide to Butterflies of North America by Jim Brock and Kenn Kaufman.

I hope you enjoy observing butterflies this summer! Here are the photos from the rearing variegated fritillary butterflies.

Cage setup with fresh pansies. 
Up close of a caterpillar. 
Feeding frenzy. 

Newly emerged butterfly. 
Time to fly!

Monday, June 29, 2020

The joy of sunflowers

By  Irene Shonle,  El Paso County Extension

This year I have really fallen in love with sunflowers. I have always liked them, but this year, I am in love. I love them because of their cheerful disposition, because they are so dang easy to grow, and even more because they are such great plants for the habitat garden.
Wild sunflowers in my garden (Helianthus annuus)

Sunflowers lure pollinators in with their tall form and bright-colored flowers and then  they reward them with abundant sources of both pollen and nectar. Both smaller bees and butterflies find an easy perch on their wide flat heads. Bees that are attracted to sunflowers include bumble bee, digger bee, large carpenter bee, small carpenter bee, leafcutter bee, sweat bee, plasterer bee, andrenid (miner) bee, and honey bees. Even the leaves of sunflower are a good source of food for a variety of butterfly caterpillars including American Lady, Silvery Checkerspot, and Gorgone Checkerspot. Later, the black, oily seeds provide food for a variety of birds such as finches, juncos, and chickadees.  Make sure to save a few seeds yourself to plant for next year.

Another reason to like sunflowers is to provide quick screening from neighbors.  If you have planted a slower-growing shrub or vine to block a view, but want more instant results, plant some of the larger sunflowers. Some of the ones in my garden are already 7 feet tall at the end of June!
Sunflowers (not yet in bloom) blocking the view of my neighbors while my apache plume shrub grows in 

You can also use sunflowers to create  a hidden, shady fort for children to play in.
Sunflower fort - picture from Pinterest

Some tips for growing sunflowers:
Plant in full sun.  Sunflowers, especially the wild-type sunflower, are drought tolerant, but will bloom better and grow taller with some water.  That said, I am astonished at how well the wild sunflowers are flowering here in our extreme drought and heat this summer.

Plant in groups to make it easy on pollinators to forage efficiently.  Don’t buy pollen-less single-stem varieties -- these are good for the cut-flower industry, but bad for pollinators.  Branched sunflowers are a much better bet, plus produce more blooms for you to enjoy.

Plant several different varieties to provide a continuous supply of flowers from late summer to fall. Look for “days to bloom” on the back of seed packets and plant a variety.  As a gardener, you can revel in colors ranging from yellows to oranges to reds, with wildly different sizes of plants and flowers. You can also sow sunflowers every couple of weeks in the spring to increase bloom time.
One of the many varieties of sunflowers you can grow - this just bloomed in my garden yesterday

Friday, June 26, 2020

I've got honeydew on my honey-do

Posted by: Todd Hagenbuch, Routt County Extension

The Futura will look brighter after a good wash.
(Well, after that and the paint job I'm pushing for...)
My honey-do list this summer is a long one. Of course, I put a lot of it on there myself, but it includes planting new gardens, tending to the lawn, weeding the existing gardens, keeping an eye out for the usual insects, (yes, I’m talking about you, Columbine Sawfly) and more. I even have some non-yard items on my list, one of which is convincing my mom that we need to restore her 1966 Ford Falcon Sports Coupe. That honey-do actually alerted me to an insect issue in my trees. How, you ask?

I took Mom’s car from her home a couple of weeks ago to get some estimates on the work. In the time since, it’s been in my driveway instead of in her garage. When I met her with the car to discuss the restoration, she questioned what had happened to her already-spoiled paint job. “Honey, what did you do?!?” she exclaimed. “This honey didn’t do anything, Mom,” I replied. “That’s honeydew.”

Nope, that's not custom paint- that's honeydew.
(At least it does bring some shine to the ol' girl!)
Honeydew? Yes, it’s a wonderful, sweet melon and my favorite scientist on the Muppet’s Show, but it’s also the term used for the sticky substance that is excreted from phloem-sucking insects. Scales, adelgids, whiteflies, and aphids all produce honeydew. They pick a spot on a plant leaf or needle and, with their specialized mouth parts, bite down and start sucking the phloem, or plant sap. As with all things eaten, what goes in must come out, and out it comes as honeydew. Then it floats down and finds its way onto things below it.

Like I did with the Falcon, you’ve probably parked a car under a tree seeking shade from the summer sun only to come back and find the windshield sticky with honeydew. Perhaps your deck and railing have become covered with the sticky substance, too, or the sidewalk under a tree. I get calls in the office asking what kind of tree it is that creates the honeydew, or what’s wrong with a tree that's ‘leaking’ sap from above. No one is thrilled to find out it’s actually insect poop that has covered their patio furniture or sunroof.

These shade seekers will find their windshields a sticky mess
at the end of the day as this cottonwood has aphids.
In most areas this time of year, aphids are the creators of honeydew. As one of the only insects that gives live birth, each aphid is born ready to birth to the next generation, and so on. This means that aphids multiply rapidly, and as more are born, more excrete honeydew. One day your deck is fine, and two days later, it’s a sticky mess. And just like that, your honey-do list now includes power washing the deck, scrubbing the outdoor furniture, and washing the car.

Honeydew does have its fans. The hum from the tree near the Falcon isn't the 289 V8 firing all cylinders, but Western Yellowjackets who feed on it and swarm the tree to find it. Ants love it, too, and will roam the plant or tree collecting it and protecting the aphids producing it. 

Plants can be sprayed with an insecticidal soap or pesticides to help control aphids, but I find that just spraying them down with a strong jet of water is effective and causes fewer issues for beneficial insects and the items below the tree. A hard rain will do the same thing and provide relief for a few days, but remember that the aphid population will rebound quickly. Spraying with water again can help keep numbers manageable.
A lower leaf from the cottonwood, sticky with honeydew
For detailed information on how to control aphids on shade trees, add reading CSU Fact Sheet 5.511 to your honey-do list. The control efforts you learn might enable you to knock a few of those other honey-do items of the page.

Thursday, June 25, 2020

Milkweeds, Garden Design and Monarchs

Photo credit: Butterfly Gardening

Have you ever wondered which milkweed is really recommended for our home landscapes?  There are only a 100 species across the United States to select, but the best is Asclepias speciosa or Showy milkweed.  One word of caution is that Showy milkweed does need space because it is considered one of the tillering species of Asclepias.   

Showy milkweed grows one and a half feet to three feet tall with blue-green pubescent or hairy leaves producing flower clusters or umbels of star-like rose colored to purple flowers in the upper axils of the stem.  It grows best in full sun with moist, well-drained soil that can be course, medium or fine. Its native habitat ranges from dry to moist savannas, prairies, roadsides, old fields, and meadows according to Lady Bird Johnson Wildflower Center. The plant has a milky sap when you break the stem, or the stem is injured in some way.  This milky sap is a latex and except for Asclepias tuberosa is found as a characteristic of milkweeds. This sap containing toxins is a defense mechanism for the plant to make the leaves unpalatable. This plant serves as a host for monarchs while hummingbirds and other butterflies feed off the nectar.

Other milkweeds to add to your home landscape can be those with NON-Aggressive root systems which are as follows:
  1. Asclepias incarnata or Swamp milkweed which is a native perennial growing three to four feet tall in full sun and consistently moist soils.  Flowering in July through August its blossoms are pale pink to rose purple.  Suggested cultivars are ‘Cinderella’ have pink to dark pink, reflexed petals, and pink to white crowns. ‘Ice Ballet’ is a white-flowering cultivar. ‘Soulmate’ has deep rose-pink flowers.  For further reading:
  2. Asclepias tuberosa or Butterfly weed a perennial which grows one to three feet tall in full sun and soil that is average well-drained soils dry to medium moisture. It does well in poor dry soils and tolerates drought. 

What would be the best arrangement or placement of milkweed in a garden?  Dr. Adam Baker of the University of Kentucky did research and presented that research in a paper titled, “Colonization and usage of eight milkweed (Asclepias) species by monarch butterflies and bees in urban garden settings,” along with Daniel A Potter, also at the University of Kentucky. 

In short, the small garden plots that were designed for this study were laid out differently.  The first had tall Asclepias host plants around the perimeter of the garden and were more isolated in their spacing from one another. This design attracted a higher number of females laying eggs on the taller plants versus the shorter ones.  As quoted from the study, “Host finding and oviposition by monarchs are influenced by species, height, age, developmental stage, and condition of the milkweed in the field (Cohen & Brower 1982, Zalucki & Kitching 1982; Fischer et al. 2015). 

The other design layouts of scattering the Asclepias in the center of the small gardens did not fare as well for attracting monarchs and nor did creating a mixed combination of Asclepias with other plants. Placing taller Asclepias around the border and keeping the plants open and accessible was more beneficial to attracting monarchs.  By doing this it is believed to be helpful for the monarch’s visual perception.  

If you live in the right location and are interested in attracting monarchs to your garden, keep these plant arrangements in mind.  

Photo credit: Teresa Howes, Julesburg, CO.

 Written by CSU Linda Langelo, Horticulture Agent, Golden Plains Area