CO-Horts Blog

Thursday, March 31, 2016

Colorado Multi-Site Woody Plant Trials

Colorado Multi-Site Woody Plant Trials
Dr. James Klett, Eric Hammond, Jane Rozum and Rob McDonald
Colorado State University, Department of Horticulture and Landscape Architecture
and Adams County Extension

Manzano Bigtooth Maple (Acer grandidentatum 'Manzano') Planted in 2013

Colorado can be a tough place to be a plant.  Options for woody plants and particularly tree selection are limited in much of the state due to climate, soils, and disease and insect issues.  Late and early frosts, dry winters with fluctuating temperatures, and calcareous alkaline soils have traditionally limited the diversity of species which can successfully be grown in many parts of the state.  Increasingly limited and expensive water resources coupled with a dry climate also make many mesic species less desirable.  At the same time, many commonly planted species have been affected by serious disease or insect issues such as Dutch elm disease, thousand cankers disease and emerald ash borer.

Pests such as emerald ash borer
 are one limiting factor in species selection

In response to this, Colorado State University (CSU) began a multi-site woody plant evaluation program to trial underused and “new” woody plants with the goal of enlarging the size of the plant palate available in the state.  The trial was started in 2002 at five different sites throughout the state.  Since 2002, there have been twelve plantings evaluating a total of sixty-four (64) different taxa.  Trial plants are evaluated based on survival, growth, ornamental appeal, and their potential to be invasive over a five year period.  In 2002, we started with five co-operating sites including three private sector nurseries, Boxelder Creek Nursery (south of Hudson, CO); Harding’s (Calhan); and Little Valley (Brighton) and two CSU research sites, the Horticultural Research Center in Fort Collins (now ARDEC South) and Western Colorado Research Center – Orchard Mesa in Grand Junction.  Originally ten replications of each plant were planted in a randomized block design.   However, in later planting the number of replications was reduced to eight.

The 2015 trial planting at Little Valley Wholesale Nursery
Over the years some of the sites changed.  A major hail storm in 2009 destroyed the planting at Boxelder Creek and that site was lost.  In 2015, we moved the Harding’s Nursery site to the Colorado Agricultural Leadership Foundation near Castle Rock, CO.  Planting continues yearly. In 2015 we planted five taxa and in 2016 plan to plant another five taxa.  We continue to take growth and performance data on woody plants to determine if any merit introduction into Colorado and Rocky Mountain Landscapes with the Plant Select® designation.
Dr. Jim Klett taking data on the 2011 planting
Woodward Juniper (Juniperus scopulorum 'Woodward') a 2015 Plantselect® 
selection and part of the 2006 trial planting

Some of these woody plants have been recommended or introduced through the Plant Select® program including Acer tataricum ‘GarAnn’PP15023 (Hotwings® Tatarian Maple); Arctostaphylos x coloradoensis (Mock Bearberry Manzanita); Arctostaphylos x coloradoensis (Panchito Manzanita); Heptacodium miconioides (Seven-son Flower) and Juniperus scopulorum ‘Woodward’ (Woodward Juniper).  I plan to highlight these and other plants which have stood out in the trials in future posts.
The 2006 plant at Harding's Nursery during the summer of 2014

Support for this project comes from Colorado Horticulture Research and Education Foundation, Plant Select®, Colorado State University Agricultural Experiment Station, and cooperating nurseries mentioned above.

Monday, March 28, 2016

Helleborus for Colorado

Posted by Jim Klett – CSU Professor and Extension Landscape Horticulturist

In our 2 winter, 3 growing season perennial trials at Colorado State University we have been trialing numerous species of Helleborus for five years.  I have been extremely impressed with their performance and hardiness and adaptability in our trials.  The common name is lenten rose and they generally grow 15-18 inches in size and 15-20 inches or more in width.  Plants are evergreen but sometimes the foliage can get battered by late winter.  If this happens, prune off the dead leaves at this time to make room for new growth and flowering.  Some gardeners mow the old foliage off of large plantings of the lenten rose for complete renewal.

The flowers start blooming in mid to late February with rose or cream speckled flowers and bloom for a long time.  The sepals are attractive for a long time after blooming.  Helleborus can reseed heavily by the hundreds under certain conditions.  Usually the seedlings are located at the base of parent plant and can flower in about the third spring.  This can create a nice effect in a natural setting.

Helleborus generally prefer a more moist organic well-draining alkaline soil.  We have them planted in partial to full shade and they have performed excellent.  They will tolerate some drier conditions in the summer.  Plants are long lived and once established, division is seldom.

We have planted many varieties of the Gold Collection® series from Skagit Gardens.  Two that appear outstanding include:  Maestro Hellebore (Helleborus x  ballardiae ‘COSEH890’).  Plant has shiny dark green foliage appearing almost black at times toward the end of the season.  Flower petals emerge a deep pink with white and mature to a creamy white with shades of dusty rose on the backside.  Flowers covered the plant from side to side and was very prolific.  Plants were compact and with good vigor.

Maestro Hellebore in mid-March
Maestro Hellebore in mid-March
Flower fades to a dusty rose color in mid-April 
Merlin Hellebore (Helleborus x ballardiae ‘COSEH810USPP #22350) flowers on this Hellebore emerged with pink color that is brighter than most and then matured to shades of dusty rose.  Blooms were held above foliage creating an impressive display.  Plants were more compact with long lasting dark green foliage and very low maintenance.

Merlin Hellebore with a deep pink color in mid-March
Merlin Hellebore flower color matures to a dusty rose in mid-April
Merlin Hellebore with dense, compact growth habit in mid-April

Hellebores are a great perennial for late winter early spring flower color that are evergreen and low maintenance.  If you do not have some in your garden try some and enjoy the early spring flower color and nice green foliage throughout the rest of the year.

Thursday, March 24, 2016

How to Help Storm Damaged Trees

Posted by Carol O'Meara, CSU Extension Boulder County

  Driving to work this morning revealed the impact of this heavy, wet snowstorm.  Young trees are bending under the weight of a foot or more of the white stuff.  Larger, older trees remain upright - thanks to stout trunks – but are lowering their branches.

 And some trees are losing limbs while others rocked completely out of the ground.  If you spot a damaged or downed tree on public property, notify your city forester’s office so they can put it on the schedule for maintenance.


Caring for trees on private property is the responsibility of the owner but if your trees are overloaded from the snow there’s no need to panic.  Some people are suggesting you grab the branch or tree and shake it, but that might add to the stress on the wood.  A better approach is to use a broom to very carefully knock off snow.  Use the broom in an upward motion to knock the snow from the branch instead of sweeping down onto the limb and adding more weight.

 If your tree has broken branches, the best thing you can do is to get the wound as neat and clean as possible.  Take a sharp knife and remove all the jagged edges of bark around the tear.  Don’t bother with wound paint – the tree will heal the wound.

 If possible, trim branches to leave a clean cut, making sure you follow the three steps for proper pruning (which prevent bark tears):

1.  Twelve inches away from trunk or from where you want the prune to be, make your first cut on the underside of the branch, sawing upwards through one-third of the branch.

2.  One-inch outward from the undercut, saw downwards through branch.  At the point of no return, the weight of the branch will snap the limb, but the undercut will stop bark tearing of the tree. 

 3.  Make your last cut just outside the branch collar, the spot where branch and trunk join.  Often, you can see a slight swelling at this point. 

 Find a diagram of this pruning method at PlantTalk Colorado.

 If you’re not sure if your tree is a goner, contact an arborist to assess it.  Those with less damage should be cleaned up, then have close attention to care over the summer.  Water them if we’re dry, and keep them healthy.





Monday, March 21, 2016

Hort Peeves: Wrong Plant, Wrong Place

Posted by: Alison O'Connor

I saw these trees today (I think they are serviceberry) leaving a restaurant near the CSU campus in Fort Collins. I was with fellow horties Mary Small and Tony Koski and we all stopped dead in our tracks to gawk and take photos.
As seen in Fort Collins...
Wow. Just wow. Talk about a "concrete coffin".
Sniffle. Poor roots.
I'm just at a loss for words...and why don't you just add insult to injury with the rock mulch!
At least the bike wasn't chained to the tree.
What really gets my goat is that they were nice trees...really nice trees. Good quality trees. I'll keep an eye on them to see how they do over the months/years. I won't argue that something green would is nice to plant near the wall to break up some of the hardscape...but maybe a taller ornamental grass would have been a better option or a decorative container? A tree is just a bad choice. The branches are already touching the wall. Any other thoughts/comments?

Thursday, March 17, 2016

Luck O' the Irish! Shamrocks rock

Posted by: Alison O'Connor, Larimer County Extension

Don't let the last name fool you...I'm German and Swedish, but on St. Patrick's Day, everyone can be Irish! And we should take the time to celebrate our clover friend, the shamrock.

Shamrocks are a member of the Oxalis family, also known as wood sorrels. The family contains over 300 species of plants, most of which grow from bulbs, though some have tuberous roots. A distinguishing characteristic of the shamrock is how it folds up its leaves at night, “hugging” the stem. The leaves re-open at daylight. The familiar plant grown for St. Patrick’s Day is Oxalis acetosella. This plant has small, dark green, triangular leaves and usually grows no more than six inches tall. Though it’s not the official shamrock of Ireland (Trifolium dubium), it’s much easier to grow indoors.
Shamrocks (Oxalis acetosella)
Why is the shamrock associated with Irish history? The most popular reasoning is because of Saint Patrick, who is credited for bringing Christianity to Ireland. History claims that in front of his congregation, he picked a shamrock from the grass at his feet to demonstrate the doctrine of the Holy Trinity. St. Patrick’s Day is celebrated on the anniversary of his death and it also symbolizes the arrival of spring. Thus, the shamrock was adopted to pay homage to Saint Patrick and announce the “season of rebirth.”
A stained glass depiction of Saint Patrick
(Photo from
Growing shamrocks indoors takes a bit of patience and practice, meaning I will never grow them. The plants like cool, moist soil and bright light, except when they are dormant. Daytime temperatures should be no more than 75 degrees, and 50 - 65 degrees at night. They do not have an extensive root system and prefer to be pot-bound. Fertilize shamrocks every two to three weeks while it’s actively growing or flowering. Oxalis plants can become leggy if there isn’t enough light, or if temperatures are too warm. If the plant begins to look “sick” and starts to lose its leaves, don’t worry—it’s going into dormancy, which happens two or three times per year. While the plant is dormant, stop watering and let the foliage die back naturally. Shamrocks “rest” for about three months, then will send up new green shoots. When the shoots emerge, move the plant back into the light and water regularly. Oxalis flowers can be white, pink, yellow, purple or red, and some varieties can reach 10 inches tall. Leaf color ranges from dark green to a deep red.
Shamrock flowers
Another oxalis you may be familiar with is the lawn weed, Oxalis stricta, also known as yellow woodsorrel. This “shamrock” has perfectly heart-shaped leaves and yellow flowers. It’s an incredibly difficult weed to control in home lawns and landscapes. It prefers low cut turf that is well-watered. To address this weed, first raise your mowing height and reduce irrigation inputs. Once the turf is healthy, oxalis will disappear. If you need herbicide assistance, select products containing triclopyr (for example: Ortho Weed-B-Gon Chickweed, Clover and Oxalis Killer). Apply according to the directions on the label.  
Yellow woodsorrel or oxalis growing in a lawn
(Photo from the University of Minnesota)
Personally, I think sticking to the "tried and true" holiday plants are much nicer than the weird ones they dye. Why do they do this?
Isn't a simple white orchid more attractive than these sickly green dyed ones?

Monday, March 14, 2016

The Snow has Melted...

Tony Koski, Extension turf specialist

Gray snow mold after the last of the snow has melted
…and people are REALLY worried about their lawns! Some are seeing vole injury. Many are seeing snow mold. And more than a few are plagued by both. While these two lawn problems may seem unrelated, they have a common cause: long-term snow cover.

You can see the "mold" (mycelium) if you look closely!
If you rough up the matted
grass you will find living
grass shoots underneath
Regarding snow mold, the most common places it is being seen is where snow accumulated on the north sides of buildings and fences, or where shoveling and plowing piled it on turf near sidewalks and driveways. As we speculated in an earlier blog that it might happen, gray snow mold has made an appearance in many Colorado lawns this year. While it looks bad, gray snow mold is rarely fatal in home lawns (although tall fescue can be killed by severe gray snow mold). Raking the matted grass to hasten its drying is really the main thing that needs to be done to get snow mold-affected grass growing again. However, if you can’t remember the last time you fertilized your lawn, a spring application of nitrogen (at least half should be slowly available nitrogen…you can find this on the label) can also help speed green-up and recovery. There is absolutely NO reason to apply a fungicide to lawns afflicted with snow mold – no matter what your lawn care company or other expert might tell you.

Vole trails adjacent to a shrub
bed that is covered with
weed barrier and mulch - an
ideal vole hangout!
Vole activity on lawns has also favored by long-lasting snow cover – especially if that snow was adjacent to an un-mowed greenbelt/native grass/natural area, or a mulched shrub bed (especially with junipers). Voles especially like living under the landscape fabric (aka “weed barrier”) that is often installed under mulch and gravel in landscape beds. Voles will venture out into snow-covered lawns from the shelter of tall grass and juniper to feed on the lawn – creating trails under the snow. The longer the snow lasts, the more trails they make and the more severely they can damage the lawn. As with snow mold injury, the turf will usually recover from vole feeding. However, where vole numbers are high and snow cover is especially long-lasting, turf may be killed by the persistent vole feeding – sometimes requiring reseeding or spot sodding.
As with snow mold injury, this
grass is already growing back
in a vole trail.

When the snow melts, the snow mold disease ceases to be a problem (ultra violet light from the sun pretty much stops its growth) and the voles are reluctant to feed on the lawns without the shelter provided by snow cover. In most cases, a little TLC will get your lawn back to where it was before the voles and snow mold visited it this winter.

Read more about voles in your lawn here and here.
Voles love living in beds covered with landscape
fabric (aka "weed barrier") and mulch

Thursday, March 10, 2016

Heavenly Houseplants

Posted By: Sherie Caffey, Pueblo County Extension horticulture coordinator


        Houseplants are a great way to bring a little green into your life before the spring growing season arrives. There are many kinds of houseplants that you can grow, and they all require different conditions in order to thrive. The first step to being a good plant parent is to find out exactly what plant you are growing, and the specific conditions that make its environment optimal. There are general guidelines that you can follow to make almost any houseplant happy.

            The amount of water that a houseplant needs depends on the species, size, and potting mix composition. One way to tell if your plant needs water is to feel the soil. If your plant has high moisture requirements, water when the top layer of soil starts feeling dry. If your plant prefers its roots to dry out a little between waterings, then feel the soil that is beneath the top layer, and water before it completely dries out.

            Most potting mixes do not contain enough nutrients for plant growth, therefore fertilizer is needed. Look for a fertilizer that is specifically formulated for your plant, or go for an all purpose fertilizer. Always follow the instructions on the label. If you notice a white build up on the soil or the container, you may have over fertilized. If this problem occurs, run clear water with no fertilizer through your soil for the next several waterings. Make sure the container your plant is in allows water to drain.

            Like any plant, houseplants can be host to nuisance insects. When buying a houseplant, inspect it for insects before bringing it home. Once the plant is home, consider quarantining it for a couple of weeks to make sure it is pest free and will not infect your healthy plants. If you notice a pest problem, contact the CSU Extension office to get specific information on control options.

            Some houseplants, such as ferns, palms, and mother-in-law's tongue do well in the low light environment of most homes. Other plants will need supplemental light to thrive. You can use a light bulb designed for house plants, or you can use two 40-watt cool white fluorescent bulbs and one 40-watt incandescent bulb to achieve a good light spectrum for growing plants. 

          So bring a little of the outdoors in, and experiment with houseplants, you'll be glad you did!

Tuesday, March 8, 2016

Baking and Cooking in the Garden

Kurt M. Jones
Chaffee County Extension Director

I was at a conference recently and was visiting with some colleagues from across the Western United States.  The conversation came around to how baking, cooking and gardening all relate to one another.  It was an interesting analogy that I will attempt to recreate for you here.

If you think about it for a while, you realize that for many of us, Baking is a prescriptive activity.  You find a recipe that you like, maybe tweak it for high altitude adjustment, but then you follow the directions and let the science of chemistry and physics turn into delectable treats.  Gardening has similar attributes.  You pick plants that will work in our growing environment, arrange them according to their irrigation needs (what we call “hydrozoning”), and provide plant care including proper irrigation, proper plant nutrition to minimize stress, and Integrated Pest Management (IPM) techniques when problems appear.  Even our current Master Gardener textbook is entitled The Science of Gardening, and employs many of these concepts for those students.

I have to admit, I may be addicted to cooking shows.  I find it fun to see cooks sweat it out when presented with a basket of mystery ingredients and they need to create a meal from unusual ingredients.  They are judged on taste, creativity in how they use the basket ingredients, and cooking technique.  In other words, they are skilled in the art of cooking based on their understanding of the base ingredients and cooking techniques. 

Gardening definitely has an artistic component as well.  Landscape Architects utilize design concepts such as line, color, texture, form, unity, scale, balance, simplicity, variety, emphasis and sequence when creating themes for the outdoor “rooms” they create.  They create rooms by considering the plants that make up the floor, walls, and ceilings in the outdoor spaces based on a family’s desires for that space, and the potential of the site where the landscape will be located.  Plant selection and placement in the landscape is much more about its “fit” into the total picture, rather than the “pick and plunk” method that many of us employ.

Much like how the creative cook utilizes different spices and herbs to elicit different sensations on the palate, the artistic gardener utilizes plant materials and other garden elements to create different emotions for those who experience it.  Understanding the science behind how to grow appropriate plants successfully and keep them healthy is much like the baker who utilizes the science to create delicacies which compliment the gourmet meal. 

It is about time for lunch, so here ends the analogy between baking, cooking and gardening.  Happy Gardening, Cooking and Baking!

Friday, March 4, 2016

Is this the year of the voles?

By Irene Shonle, CSU Extension in Gilpin County

Last year was a bad year for voles, but this year seems to be off the charts!  I have gotten many calls, and all of my colleagues are mentioning the same thing.   Now that the snow is melting off the lawns, people are looking in horror at the trails all over their lawns, and perhaps also looking at dead junipers or other shrubs from the voles girdling action.  
The high vole numbers may be due to the moisture we’ve gotten the past two years.  It’s caused a lot of grasses and forbs to grow luxuriantly, and this has led to lots of fat and happy voles that have of successful litters… which leads to …. more voles!

If you’re not sure whether you have voles or not, you may like to see this new fact sheet that helps identify what animal caused the damage you see in your lawn:

The good news here is that voles have pretty predictable boom and bust cycles.  Population explosions (right now) are followed by intense predation and other stressors that bring the levels back down.  So, even if you do nothing, you will probably find fewer voles in the future.  And it may bring a little comfort to realize how ecologically important the voles are – coyotes, fox, bobcats and hawks all depend on them.  In other words, we would never wish them to go away altogether.  And for that matter, they never WILL go away altogether.  If you have voles now, you probably will get voles again.

However, I think most of us would like them out of our gardens and lawns, especially when a few too many have moved in - like this:
Voles trails become apparent in the melting snow
To repair damage to lawns from runway construction, rake, fertilize and water the affected area.  The lawn should recover when the grass begins to grow.  Extensive areas may need reseeding.
For the most part, trapping is the fastest way to handle voles, and has the least potential to cause secondary environmental damage. It can seem daunting, but it is pretty easy to trap down the population that has settled in your yard in just a couple of days.  Poisons can be used, but there is the possibility of secondary poisoning of all the critters that could then eat the poisoned vole (including your dog or cat).  For more information on how to trap or use toxicants, please see:

Some preventive action in the fall can also be helpful – mow your lawn closely to reduce the tall grass that provides a safe haven for voles.  Since they are food for so many species, voles are rightly cautious in exposing themselves unnecessarily. If you live near an open space area, see if there is a way to mow a swath of the native grasses along the fence line to keep them from crossing over into adjacent lawns. 

Another idea – and this is not research based (yet anyway), but it does make a lot of sense to me, is to shovel a swath of your lawn in the areas where you usually see a lot of vole activity and damage in the spring-- similar to mowing the grasses above. Voles can move in to even a short lawn under the cover of the snow, since the snow keeps them just as safe as long grass does from predators.  If you remove the snow, it might just blow their cover.  I'm not suggesting you shovel your whole lawn -- just 5-10 feet by the fenceline where the voles get in. If you try this, please report back!