CO-Horts Blog

Friday, April 28, 2017

To Cover, or Not to Cover? (winter is back!)

Posted by: Deryn Davidson, Boulder County

For the past several weeks it's seemed that the warm weather was here to stay. But, we all have to remember that we live in Colorado and you NEVER know what Mother Nature has in store for us here. Over the next two days, much of CO is predicted to get below freezing temps overnight and many people are asking if their plants will survive. Well, as usual, it depends...

A freeze is when the temps drop low enough to cause the water in plant tissue to turn into tiny ice crystals and the next day your plants turn to mush (destroyed plant tissue). A frost is when there is a lot of water vapor in the air and temps drop low enough to freeze that vapor. The result is frost on top of plants. We can get light frosts, that don't actually freeze plant tissue. The different is based on: how low (below 32F) the temperature get, how long the low temp lasts, what species of plant you have, and where the plant is located (sheltered or out in the open).

There are some plants that will be affected by this cold-snap and there are measures you can take to help protect them:

  • Covering plants is the most common. You can use old sheets, blankets, frost cloth, burlap sacks, etc. Flower pots or large trash cans turned upside down can also be placed over plants. If you use something heavy like a blanket be sure that you have stakes or something else besides the plant to hold up the blanket. You don't want to crush the plant while you're trying to save it from the freeze! Cover the plant in the evening to try to trap some of the heat that has built up during the day, then UN-cover the plants the next morning once the sun is out. 

Grouping of pots at DBG covered for late April freeze
Nursery stock covered in preparation for the April freeze

  • Watering plants can help, but you would have needed to do that a few days ago. Moist soil retains more heat and will raise humidity levels which can help reduce frost damage.
  • Mulch can provide some protection if you have a nice layer down. You can mound it up around plants, but delicate/tender plants won't like to be covered with a thick layer of mulch. 
These precautions can help, but we all have to realize that some plants just won't take the cold well and may be set back by the low temperatures, others will make it through just fine. If you have plants that seem particularly tender, go ahead and give them some extra protection. 

I have to give a nod to Jack Frost and Mother Nature, always keeping us gardeners on our toes here in CO!! Good luck everyone, I hope your gardens come through just fine!!

Wednesday, April 26, 2017

Plantin' in the Rain I'm Plantin' in the Rain

Posted by: Curtis Utley Jefferson County Extension

While a reality or drudgery in many parts of the US, the opportunity to plant in the rain is a luxury not often possible in Colorado. The benefits of being able to plant at the beginning of a rainstorm are many. Purchased potted plants require some root manipulation before planting.

Container plant root ball
You must either cut the outer inch of the rootball off to prevent the continuation of circling roots or you must tease the rootball apart so you can lay the root system out carefully into the planting hole.
Digging planting hole
This all takes time and plant roots are extremely sensitive to dry air which is common in Colorado. By planting in a rainstorm you afford yourself some time to tease the root system out of the ball and provides a larger window of time to adjust the root system in the planting hole as you layer in the backfill soil.
Laying out the root system
Close-up of root system re-orientation 
In dryer times if too much time is taken in transplanting transplant shock can occur when the root system desiccates. Drought stress may also occur as the water demand by the leaves for transpiration is not met. These stress factors are greatly avoided when planting during a rain shower because the root system doesn't desiccate and the leaves of the plant are not actively transpiring water to cool themselves when raindrops are falling.
 I found three Jostaberry plants for a song at a local garden center and bought them with excited anticipation of jam in my future.
Rain can also help settle the soil around the root system. It is not advisable to plant after a lot of rain has fallen because the soil has the potential to become compacted as you plant. When the soil particles are well lubricated it's best to stay off of the soil to avoid destroying soil structure, but at the beginning of a rainstorm, before the soil is saturated  is a great time to install new plants in your garden. It may not be the most comfortable time for you to be out in the garden but gardening is a labor of love and if you can establish new plants when they are less stressed you will have more gardening success. Keep in mind that Colorado rain events can be intermittent or short at best.
Watering to settle the soil around the root system
In this situation it is still advisable to water in your newly planted plants to allow the soil to settle around the root system. If air pockets remain around the root system of your new plants, the roots can still desiccate and the plant will not thrive.
A flooded planting hole assures the elimination of air pockets 

Monday, April 24, 2017

Dwarf Mistletoe in Ponderosa Pines posted by Mark J. Platten

I’ve received numerous calls regarding southwest dwarf mistletoe (Arceuthobium vaginatum subsp. cryptopodum) in ponderosa pines over the years.  They are leafless, parasitic plants that infect several species of conifers, producing root-like structures that grow in the living tissue, where they extract both nutrients and water from their host plants.  
The southwest dwarf mistletoe is relatively host-specific and generally doesn’t affect other tree species in our region other than the occasional limber or bristlecone pine. 

Symptoms and Signs
From a distance, coniferous trees infected with dwarf mistletoes may appear to have yellow foliage, reduced foliage, abnormally dense green and distorted foliage known as witches’ brooms, and mortality of the upper portion of the affected tree.
The first symptom of dwarf mistletoe infection is a slight swelling of the bark at the infection site.  The parasite is identifiable when shoots protrude two to three years after infection. 

Damage to Host Trees
The mistletoe and subsequent witches’ brooms extract resources from the tree and may cause mortality.  Death of the host tree occurs slowly in most cases and depends on the severity of infection, vigor, and size of the tree.
Mistletoe severity is established by dividing the crown into equal thirds and rating each.  If there are no visible infections, that third of the crown is rated 0; if 1 to 50 percent of the branches are infected, the rating is 1; and if more than 50 percent of the branches are infected, the rating is 2.
Add the ratings of each third to get a total rating.  Ratings of 3 or less are considered light, 4-5 moderate, and 6 heavy.  Life expectancy is based on tree diameter and severity of infestation.  For diameters of nine inches or less, the range is 7-30 years.  For diameters greater than nine inches, life expectancy is in the range of 10-60 years; with the low number reflective of heavy rating and the high end based on light ratings.

Their life cycle, from initial seed germination to producing fruiting bodies, is 6-8 years, providing time for management.  The sticky seeds literally explode via hydrostatic pressure at almost 60 miles per hour!  Seeds that adhere to young branches of susceptible trees germinate and the mistletoe rootlet penetrates the bark.  Dwarf mistletoe seeds generally are dispersed in August and early September.  Birds and other animals can occasionally spread the seeds some distance to uninfected trees. 

Although mistletoes cause a gradual decline of plant health, trees may become stressed, attracting mountain pine beetles, Ips beetles, and twig beetles that may kill the tree.  Mistletoe management options include branch pruning, tree removal, and planting resistant tree species.

Branch Pruning and Tree Removal
Pruning witches’ brooms and removing infected trees is the best management measure available to reduce or eliminate dwarf mistletoe infestations in stands of high-value trees.  First, remove severely infected trees (trees rated 5 and 6) or those with only a few live branches.  It is not necessary to completely eradicate the mistletoe, since this may require removal of all trees.  Pruning infected branches and removal of a few heavily infected trees can keep a green forest on the property.
Pruning the lower and the largest witches’ brooms from lightly to moderately infected trees (trees rated 1 to 4) can improve the health and allow these trees to survive for decades.  Examine trees every two or three years, removing any newly infected branches.  Mistletoe shoots die as soon as the tree branch is cut, so no special disposal is needed.  If space allows, create a 50 foot buffer zone between infected trees and healthy trees that may be affected.  Contact a professional forester, the Colorado State Forest Service, or other professionals to obtain help in these decisions.

Hawksworth Six–class method for evaluating dwarf mistletoe infection (Hawksworth 1977)

Plant Resistant Tree Species
Planting resistant or non-host tree species in areas with infected trees will ensure that trees will be in the area even after the infected trees are remove.

Chemical Sprays
Ethephon is a growth-regulating chemical that can be used to remove mistletoe shoots and reduce seed production.  This treatment does not kill the entire mistletoe plant, just the shoot. Re-treatment is necessary until infected trees are removed, mistletoe infections are pruned from the tree, or new non-host trees are planted.

For more information on dwarf mistletoe, please see CSUE Fact Sheet:

Monday, April 17, 2017

Atomic Gardening

By Cassey Anderson, Adams County Extension

Photo Credit: 
Listening to a podcast awhile back I learned about a form of gardening I had never heard of before. In the 1950s scientists realized that, in the presence of gamma radiation, plants would mutate.  Interest in crop mutation grew out of a combination of food insecurity as a consequence of World War Two and the discovery of the power of the atom. In the fallout from the atomic bomb in Japan, people noticed that sesame plants near the blast site grew much larger than non-irradiated sesame plants. This sparked an interest in scientists and lay persons alike seeking to see if they could safely replicate these effects.

Gardens, named atomic gardens, were arranged in a radiating pattern with a radioactive source at the center, typically cobalt-60 (ironically these gardens resembled the warning symbol for radioactivity). While the plants nearest the radiation source would often be stunted or die, those further away were likely to exhibit a wide variety of mutations.  The results were highly unpredictable but there were some successes from irradiated seed. This was the period in which radiation was perceived as likely to make things stronger, rather than weaker. Think Spider Man, Godzilla, Atomic plants; they all fit in the same optimistic mentality of the benefits of radiation.
An early Atomic Garden.
Photo courtesy of

A woman in Britain, Muriel Howarth, started the Atomic Gardening Society to encourage homeowners to plant seeds from these irradiated plants. Howarth even published a how-to guide on Atomic Gardening, titled the same. Her goal with her home gardeners, who she called “Atomic Mutation Experimenters”, was to work to help scientists produce food more quickly for more people and progress mutations to promote food security. The seeds from the plants grown in this manner were not radioactive, but did have radiation induced mutations.
Photo courtesy of: 

In one of the research gardens in Rhode Island plants placed in the radioactive garden included plants ranging from strawberries to sugar maples. By 1958 government labs around the world had set up atomic research gardens. Muriel Howarth tasked her Atomic Mutation Experimenters with keeping data on the progress of the plants they grew out for scientists. Many seeds did not produce a plant or a satisfactory product, as blasting a plant with radiation receives erratic results.
Current gamma garden at the Institute of Radiation Breeding in Japan.

Home gardeners became discouraged with limited results from their research plants, and even government programs with dedicated personnel produced only limited results. The final program in the US was discontinued in 1979. However, there is still a working “gamma garden” in Japan, the Institute of Radiation Breeding. There is also a collaboration of scientific research focused on nuclear techniques in food and agriculture called the Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture to help improve global food security and promote sustainable agriculture development.

There are some survivors in our food supply from this strange period of atomic gardening. You may be familiar with the Rio Red grapefruit, and ‘Todd’s Mitcham’ peppermint for oil production, they are both byproducts of atomic mutation experiments. The Joint FAO/IAEA division lists over 3200 official mutant varieties from 214 different plant species. 

Thursday, April 13, 2017

FireWise Landscaping

FireWise Landscaping

 By Linda Langelo, CSU Horticulture Program Associate, Golden Plains Area
Fire can happen on any landscape, at any time.  Incorporating preparation and prevention can assist with lessening the threat of fire.  
A fire on the plains can be effected by three things:
·        Surface fuels
·        Fine, fast-burning fuels
·        Usually driven by high wind
Photo Credit: Colorado Forest Service, Boyd Lebeda

What can you do when faced with a grass fire that travels quickly?  What preparations do you need to put in place around your home, long before a wild- fire? 

Aside from all of the above information, before fire season, stand back and look at your landscape differently can help prevent disaster to your family’s home.

First, according to the Colorado Forest Service when renovating your landscape around your home, this requires a defensible space.  This space serves as a buffer between your home and the trees, shrubs, perennials, grass and any wildland area that surround your home.  Do you have an evergreen planted up against your home? Does the ground slope away from your home?  What types of are established vegetation on your property?  All are factors to your ability to mitigate fire damage to your home.  CSU Forest Service recommends keeping your defensible space clean of trash and debris.

Second, everyone’s home has weak spots and hardening your home means using construction materials that can help your home withstand flying embers and shore up those weak spots.  Do you have a wood deck that attaches to your home? Are there garden tools with wooden handles or brooms or other highly flammable materials under the deck such as pine needles or leaves?  How often do you clean your gutters of debris? 

Third, have a Family Disaster Plan that has evacuation routes in place in case your family is asked to evacuate, a meeting area outside the fire hazard area and a Disaster Supply Kit.  This kit needs to last for at least 3 days and contain your family’s and pets’ necessary items.  Some of these items might be prescription medicines, cash, water, clothing, food and first aid.

Preparation goes a long way towards the success in a fire disaster or any disaster.  Disasters can put people in a panic mode.  If you have a plan, having a disaster supply kit insures that you may not forget medicine or something equally critical and the plan helps save lives. 

Now that you have an idea of what fuels a fire and what you need to do, you can add fire-resistant plants to your property and still have a beautiful landscape. There is a factsheet listed below which I have referenced in this article.  There are some wonderful native plants such as some of the perennial native forbs(wildflowers):

·        Echinacea purpurea, Purple Coneflower

·        Ratibida columnifera, Prairie Coneflower

·        many different species of Penstemon. 

Beyond these there is a wide list of non-native perennial choices from the FireWise Plant List on the FireWise Plant Materials Factsheet:

·        Ajuga reptans          Bugleweed

·        Lamium spp.            Dead nettle

·        Armeria maritima   Sea thrift

There are a number of shrubs and trees from which to choose from the same factsheet:

·        Prunus cerasifera               Flowering plum

·        Amelanchier alnifolia        Saskatoon alder-leaf serviceberry

·        Shepherdia argentea         Silver buffaloberry

·        Crataegus spp.                    Hawthorn

Here are some CSU links for Fire-Resistant Landscaping and FireWise Plant Materials that you can access for guides also used as references for this article:

CSU Quick Guide Series – Protecting Your Home from Wildfire: Creating Wildfire-Defensible Zones formerly CSU Extension Factsheet 6.302 –link:

CSU Forest Home Fire Safety Factsheet 6.304

CSU Fire-Resistant Landscaping 6.303

CSU Fire Wise Plant Materials 6.305

Monday, April 10, 2017

More Bees Please!

By:  Kelley Rawlsky - CSU Extension, Broomfield

Thinking back to my childhood days of sprinting across grandma’s clover lawn barefoot trying to avoid stepping on and consequently getting stung by bees, I never thought I’d be one to promote increasing their population. If you have ever stepped on a bee, it is quite painful. The stinger of the honey bee is barbed and embeds into the skin, and the stinger and poison sac are left behind. Does the honey bee really die after stinging? Unfortunately, yes.  

After studying horticulture and learning the importance of bees and other pollinators, I am firmly now on their side. Honey bees, in particular, are exceptional pollinators. Many crops, including apples, pears, peaches and melons, are dependent on them. CSU Extension has estimated the value of this pollination, which is provided freely from the local honey bees for our crops here in Colorado, at greater than $20 million annually. This doesn’t even include the several million dollars of honey and beeswax products that are also produced. So, bees are important!

We’ve all heard about the declining bee population. The reasons why this is occurring are varied and numerous, but the good news is we can do our part by planting more pollinator friendly plants in our yards. This will help the bee population by giving them nectar and pollen, but it will also help draw these pollinators to our yard so they can help pollinate our own edible gardens. 

 Attracting more bees to the yard is mostly beneficial, but if you or someone who frequents your yard is allergic to bee stings, then it might be a good idea to take a pause and rethink your approach to including a pollinator garden. Approximately one percent of the population develops hypersensitivity to bee or wasp stings which can then result in difficulty breathing, dizziness, nausea and hives. Symptoms, such as these, may require immediate attention from a physician.

In my own yard, planting a lot of pollinator plants has had some unintended consequences. Our 10 year old labrador retriever likes to snatch up flying, buzzing insects with her mouth. It’s quite obvious that she gets stung most of the time because of the way she shakes her head afterwards with a puzzled look. As many times as I try to explain to her that bees are our friends, she just doesn’t learn.

What to plant? Flowers! Here are some good choices that are water-wise and well adapted to our climate: Agastache rupestris (hummingbird mint), Echinacea purperea (purple coneflowers), Penstemon x. Mexicali, and Perovska atriplicifolia (Russian sage). For a more detailed list, see: Gardening for bees - or not! by Whitney Cranshaw, ColoradoState University

In case you're wondering, not all of the pics included are of honey bees. Maybe there's an entomologist out there who can identify them for us!