CO-Horts Blog

Tuesday, March 26, 2013

Perennial ‘Top Performers’: Information from the CSU Two-Year Perennial Trial

By: Jim Klett, Professor and Extension Landscape Horticulturist, Department of Horticulture and L.A., Colorado State University

Now since it is officially spring, industry professionals and gardeners are thinking of growing and planting perennials. I hope you will consider these ‘Top Performers’ from the CSU Trials. These perennials were planted in 2010 and researched for 3 growing seasons and 2 winter periods.  For more information on the perennial trials, visit our website. 

Buzz™ Butterfly Bush
Buddleia davidii ‘buzz™’ PPAF series, (Buzz™ Butterfly Bush Series) – This entire series was noted for excellent flower production and dense growth. Range of colors in series was Blue Violet, Ivory, Pink Purple, Violet and Magenta. These more compact Butterfly Bushes work well as a mixed border plant.

Gold Collection® Lenten Rose
Helleborus x ballardiae ‘Gold Collection®’ series, (Gold Collection® Lenten Rose series) – The plants were noted for early blooms (March) with flowers facing upright and dark glossy green foliage year round. These plants make a great groundcover for a shady area. Flower color varies from a pink blush with yellow interior to pink blush on chartreuse petals.

Fireball Bee Balm
Monarda ‘Fireball’ PP #14,235, (Fireball Bee Balm) – Plants are prolific bloomers in July with wine colored blooms on sturdy stems with no lodging, even with overhead irrigation. They have superior mildew resistance and great for the back of perennial border.

Phlox paniculata ‘Classic Cassis’ PPAF, (Classic Cassis Perennial Phlox) – Plant has a long bloom time with big bold flowers. Flowers are a bright pink color with hints of mauve which start in June and continue well into August. Plants have good clean green foliage throughout the season.

Pina Colada Perennial Phlox
Phlox paniculata ‘Pina Colada’ PP#19968, (Pina Colada Perennial Phlox) – Pure white flowers are impressive against the dark green foliage from June into September. Growth habit is compact and spent flowers drop off the flower panicles that give plant a clean look throughout the season.

These five perennials are a must for producers, retailers and gardeners for the 2013 growing season.

Saturday, March 23, 2013

What does phenology have to do with crabgrass!?

By Alison O'Connor, Horticulture Agent, Larimer County

Since our CSU Rams just lost in the NCAA basketball tournament (and my Cyclones were just robbed by my other alma mater on a buzzer beater), I texted the Turf Man, Tony Koski, about when to apply my pre-emergence herbicide (yes, slow day here in northern Colorado).  Turns out that there's a really cool trick you can use to time your application: using the blooming time of certain landscape plants.  This, boys and girls, is what's known as phenology.  Don't you love science?

Phenology is officially defined as, "The scientific study of periodic biological phenomena, such as flowering, breeding and migration, in relation to climatic conditions" (courtesy of 

There's been several scientific studies, summed up nicely here in this Purdue article, about what plants can be reliable indicators of when to apply your crabgrass preventer.  One is the glorious golden yellow blooms of forsythia...another is the white blossoms of Callery pear...and another are those dainty pink (or white) redbud flowers.  When these plants are in bloom, or near bloom, it's time to apply your crabgrass preventer.  To me, this is SO much easier than calculating degree days or measuring soil temperature.  Or asking Tony every year...

I was just in Portland earlier this week visiting family, and their forsythia were in full bloom.  I hope my brother put down his crabgrass preventer.  But somehow, since he has a one-year-old, I'm guessing it was put on the back burner...

The wonderful Oregon Garden in Silverton.  Look at those magnificent forsythia!
It's important to remember that you have a window of time to get this done.  Tony recommends that you apply your crabgrass preventer by April 1 in Denver, April 15 in Fort Collins and ASAP if you're further south or on the west slope.  Just remember, these products need 0.5 to 1" of water after application to make 'em work.  

In the meantime, enjoy the snow and look for those blooms...a sure sign that spring is coming!

Wednesday, March 20, 2013

Choices, choices, choices...

Posted by: Darrin Parmenter, La Plata County Extension

A couple weeks ago the kids (ages 7 and 9) and I planned the 2013 vegetable garden. Yes, I realize that we are late to the game, as this probably should have been done earlier. But I am an Extension Agent – I’m always late. The kids were excited to impress upon me how many different veggies they are willing to plant and try; however, they were just as quick to point out what they did NOT want.

Beets? No. Too bad kids, beets made the cut. 

What about daikon radish? “No. Wait. What is it? Um, still no.”

Potatoes? An immediate ‘no’ from my daughter – more on this a little later.

But they do get excited about numerous other crops – more than enough for our garden space. Carrots, snap peas, cherry tomatoes (notice a flavor trend here?), lettuce, beans, cucumbers, and squash will quickly fill out the beds. As I constantly tell my adult students, I have learned through years of mistakes that it is a much more efficient use of garden space to grow what you, or your family, like to eat. While I love rutabagas, and I am often saddened by the lack of love they receive, they take up a lot of space in my raised beds, and on more than one occasion, some have sat in the vegetable crisper for way too long. We grow crops that we tend to eat often (carrots, lettuce, squash, beans), preserve (tomatoes and beets) or store (potatoes, onions, garlic). Even with that conservative approach, the family always likes to throw in a couple wildcards: watermelon radishes, rainbow carrots, and in 2013, they (okay, me) chose shishito peppers.
Back to the potatoes. My daughter, who has a picky palette, is not a supporter of the spud. Understandable, but here’s the rub: a couple hundred years ago, a French gentleman by the name of Antoine-Augustin Parmentier, who for the sake of this story was most definitely an ancestor of mine, championed the potato as food fit for kings instead of its up-to-then use as animal feed. 

In fact, in 1772, the Paris Faculty of Medicine (I am assuming they were important) declared that potatoes were, in fact, edible. 

Unfortunately, my daughter has yet to give credibility to this institution, as she thinks they taste like the dirt from which they came. So her disdain, coupled with the fact that potatoes got me into and through graduate school has me on a quest to one day change her mind.

But I won’t make my daughter eat potatoes because I want her to enjoy all the other parts of the garden that she does like. I also want her and her little brother to understand – and enjoy – everything else that comes along with gardening. The bugs, earthworms, and dirt will always bring a smile. 

Yet more importantly, at least I hope so as this is my only try at parenting, is to impress upon them how cool it is to watch a plant complete its life cycle; or the reason why we grow some of our own food (my son still wishes that we could grow hot dog plants); and maybe best of all, is that the garden is a place for all us to enjoy. 

Isn’t that what it’s all about? 

Friday, March 15, 2013

Save the Blooms - Don't Prune Too Soon

Posted by Andrea Cummins, Douglas County Extension

Ah, spring is here…at least it feels like it today. And the forecast is looking good for the next week or so, maybe we are finally over the hump? Well time will tell, but you have to enjoy it while we can during the unpredictability of March. I know this kind of weather makes me look out my office window and plan a weekend of cleaning up my yard. It’s time to check for bulbs poking out of the mulch, cut back ornamental grasses and Russian sage, and prune shrubs to clean it all up a bit right? “Yes” to the first two, but only “maybe” to the last.

Pruning this time of year can lead to unfortunate results. You need to know what type of shrub or tree you have prior to taking out those pruners and cleaning up. If you aren’t careful, you might cut off all those flowers you wanted the shrub for in the first place.


Spring flowering shrubs (think lilac and forsythia) set flower buds in late summer or early fall, on old wood. Pruning too late in the year will result in reduced flowering for the next spring -- the time to prune these plants is in early summer right after they are done flowering. Summer blooming shrubs (Rose of Sharon and some hydrangea) can be pruned in March and early spring prior to new growth. These types of shrubs set flower buds on the new wood each year, so it is safe to prune them in the early spring.

Don't cut here!

Think before you prune in order to make sure you will have the blooms you have been waiting for in the next few weeks. For more information check out,

Tuesday, March 12, 2013

A Tale of Two Winters

Posted by Susan Rose, Tri River Area Extension

Grand Junction – Samples have been coming in to the Extension office daily of dead and dying evergreens.  While Austrian pines seem to be suffering the most, they are not alone; Scots, ponderosa, and mugo are coming in with brown or tan needles, often with bands of darker brown and only a little green.  Even the occasional Colorado pink spruce sample is showing up.  Only the pinions seem to be largely immune.

With one exception, there is no indication of any disease or insect problems on these samples.  They are suffering, quite badly, from severe winter desiccation, the result of two years in a row of severe winter drought.

These two winters could hardly have been more different.  A year ago, Grand Junction was experiencing record high temperatures in the upper 70’s.  Inevitably, this early season of growth-promoting, dormancy-breaking warmth was followed by a late hard frost.  Many of these evergreens, hit at a tender stage, lost all their terminal buds.  Their needles began showing the brown banding of drought stress.

This winter you may have noticed that we were unusually cold.  A snowfall on December 19 brought the temperatures crashing down and a temperature inversion set in for a couple of months.  You may have seen the reports of air quality in Salt Lake City?  Well, Grand Junction wasn’t far behind.  While the humans headed for the hills seeking warmer temperatures and cleaner air, the trees were not so fortunate.

Ponderosa pine with drought stress.  Note the healthy tree to the right -
its roots are on the north side of the berm and the stressed tree's roots
are on the south side.

People often want to believe that snow cover equals moisture, but not when the temperatures are so cold.  In a process called sublimation, water changes from a solid to a gas without ever becoming liquid.  It actually draws moisture out of the soil, not that we had any to speak of to begin with!   So, another very dry winter, but this time it was too cold to water.  All we could do was wait until the winds came and the air temperature warmed up on its own, though some residents had creative ideas regarding the use of the orchards’ wind machines to blow that nasty inversion out of the valley.

The one exception I mentioned earlier is an insect problem that seems to be fairly unique to our area, at least in terms of severity.  Austrian pines in particular are often attacked by black pineleaf scale here, and perhaps because people don’t notice it until needles start to brown these infestations often do become quite severe.  I have never seen this insect infest a healthy, vigorous tree, but I am seeing it on a lot of trees right now.

Black pineleaf scale on Austrian pine
David discussed last week how critical it is to ensure that our woody plants get a good soak in the fall, to go into winter with moist soil around their roots.  During extended periods of very dry weather over the winter, supplemental moisture every month or so helps prevent root death from dehydration.  This needs to be done on a day when the air temperature is above 32 degrees F.  While we could have attended to this during the winter of 2012, it wasn’t possible for us under the severe cold conditions of the 2013 inversion.  And our evergreens, which continue to transpire even in the winter, suffered.  The drought that didn’t kill them off a year ago probably succeeded in many cases this time around.  All I can advise people right now is to water, and wait and see.

Thursday, March 7, 2013

Dry Soils and Tree Watering

Dry Soils and Spring Watering of Trees,

Posted by David Whiting, Dept. of Horticulture & LA, CSU
March 7, 2013

I was out digging some winter carrots from the garden on Saturday and was amazed at how dry the soil is.  This could have implications for our trees, shrubs, and perennials.  We often talk more about the winter watering of trees and shrubs than what many of us actually get out and do winter watering.  The reality is that many landscape trees and shrubs are not winter watered, and seem to get by, sometimes.  A few of years ago, I kept telling myself that is rather dry and I should get out and water.  However, being busy, I did not make the time and I paid the price with dieback on an arborvitae.

Winter burn on evergreens, paying the price of knowing that the soil was dry but not making the time to winter water.

So while tradition speaks of winter watering, what the science say about it.

Fall watering – If we go into the winter season with dry soils (Colorado is normally dry in the fall without landscape irrigation), woody plants can lose around 20 degrees of hardiness.  That is a tree, which would normally go down to -20 degrees F, would be damaged at 0 degrees.  A tree that would normally go down to -10 degrees F, would be damaged at 10 degrees F.  Even without extreme cold, winter injury can occur on woody plants due to a dry fall/winter season. 

The take home message is that it is very important to fall water woody plants before turning off the irrigation system. 

Southwest bark damage is a symptom of drought.  It is most common on trees surrounded with hardscape features.  The hardscape reduces soil moisture levels, and reduces root spread potential.

Spring watering – Absorbing roots (feeder roots) grow in multiple flushes through the growing season.  That is a flush of root growth followed by a maturing periods with reducing water and nutrient uptake, followed by another flush of growth.  In our climate, around five flushes of absorbing root growth occur per year. 

The first flush of root growth will occur when soil temperatures rise to the mid- 40s.  However, this will occur only if soil water is available to support the growth.  If the soils are dry, growth of these absorbing roots will be delayed until moisture becomes available.   With a dry spring, we could miss the first of five flushes of absorbing root growth!  In dry years, the lack of soil moisture will directly reduce absorbing root growth potential for the season, and thus seasonal photosynthesis, tree vigor, and growth potential.

The take home message is to start spring watering trees when soil temperatures reach the mid-40s.

In dryer soils, absorbing roots also cycle into maturity more quickly, reducing water uptake potential.  If the absorbing roots overly mature (due to dry soils preventing the next flush of root growth) future growth flushes could be delayed for weeks, months, or even years!



Monday, March 4, 2013

Crooked Aspen Mystery -- Posted by Irene Shonle

Hiking around Kebler Pass in the fall is a feast for the senses -- I was reveling in all the brilliant gold in the leaves of the aspen, intoxicated by the beautiful day.  So I was a bit suspicious of my state of mind when  I came across this curious stand of aspen (luckily, I took photographic proof):

All of the trees in one particular grove had a pronounced crook at the base.  As I looked around, all the crooked trees seemed to belong to the same clone (aspen form large stands (clones) of trees that have the same genotype; they are connected underground by their rhizomes).
What the heck was going on?
 I looked further afield to notice that the clone just on the other side of the trail (in the background of the picture above)  was your standard straight-arrow aspen. So, it seemed unlikely that it was the soil.   I looked around a little more carefully, and noticed that aspen of different ages within the clone all had the same curious bend, so I could rule out a one-time area-wide event.  Plus, we were miles from any road.

 Beyond that, I had no idea what was going on.  I had never seen such a thing.

When I returned home, I emailed the pictures to a variety of people, but no one had seen it before.

My curiousity piqued, I turned to the internet and found this interesting page on a famous stand of crooked aspen in Canada:

In their grove of even-more-crooked aspen, while no one knows for sure what's going on, they found that the crooked trait still held  even when the plant material was propagated  in a lab or in a field.  This indicates a genetic mutation. There is some evidence that lack of strength of the shoots at critical times during the growing season may be involved.

Their trees are "bent" in a different kind of way so it's not clear that the mechanism is the same in both clones, but I bet that if I were to propagate the Kebler pass clone, I would find there is a genetic mutation at play here as well.  Anyone looking for a good research project?