CO-Horts Blog

Thursday, July 28, 2016

What is a weed?

By Irene Shonle, CSU Extension in Gilpin County

What is a weed? I think most of us have seen that cute little quote “A weed is just a plant whose virtues haven’t been discovered yet.”  This quote aggravates me to no end because it implies that any plant that has a known virtue cannot be a weed. And that all plants in all ecosystems are fine; we just have to look for their virtues.

Most savvy gardeners and people who manage open space, rangelands, or agricultural lands know that this is not the case.  There are definite bad actors that aggressively spread and cause harm to ecosystems and agricultural settings.  Plants that have the previous two characteristics AND are alien plants meet the criteria for a state-listed noxious weed, and thus become illegal to grow or sell in Colorado.  For more information on these weeds, please go to the Department of Agriculture website:
Leafy spurge - a list B noxious weed in Colorado

Not all alien plants are noxious weeds or even weeds at all.  Some can be fairly aggressive (field penny cress, small yellow alyssum, dandelion) but still not rise to the level of a noxious weed.  Some are merely nuisances in our landscapes (Shephard’s purse, prostrate knotweed).   Many are nicely behaved garden plants (Delphiniums, Iceland poppy, tulips).
Prostrate knotweed, an alien nuisance weed

But in our quest for novelty in our gardens, some of the alien ornamental plants we have brought in have turned out to be noxious weeds – even though they have the virtue of being pretty.  And they quickly spread outside the bounds of a garden, finding niches in soil disturbed by construction, travel, recreation, etc. When they grow unchecked, they can displace native plants, reduce biological diversity and alter ecosystem processes. These impacts affect birds, pollinators and mammal populations which depend upon native plants for food, shelter, and protection from predators.

The worst ornamental invaders across all of Colorado include: purple loosestrife, ox-eye daisy, Russian olive, tamarisk, Bouncing Bet, Dame’s rocket, Dalmatian toadflax, yellow toadflax (aka butter and eggs), Mediterranean sage, common tansy, bouncing bet, scentless chamomile, and myrtle spurge. 
Oxeye daisy - a list B noxious weed

What makes the weeds so invasive?
There are five key traits that allow them to dominate natural plant communities: they have abundant fruit and seeds, effective dispersal mechanisms (either by seeds or strong, creeping roots), they are rapidly and easily established, they grow quickly, and they have aggressive, competitive behavior. Even if they are well-behaved in their country of origin, they arrive in this country without any of the mechanisms that keep plants in check, such as insects, disease, and competition.

Is it possible to plant invasive ornamentals responsibly?
Not really. As soon as the "responsible" gardener who knows about the plants invasive characteristics is out of the picture (moves away, gives away cuttings or transplants, goes on vacation), the plant has the chance of becoming a problem. Often seeds can be eaten by birds, carried by cars, dogs, or the wind and then get established in new locations, unbeknownst to the gardener. Gardeners, no matter how diligent, cannot control for natural processes, most of which rule the world of plant invasions.

Dame's rocket - a list B noxious weed, often found for sale in seed catalogs as an "old fashioned favorite."
What can you do to help?
Become familiar with invasive species and report their presence on public lands to the agency in charge.

Choose native (natives (they will never become noxious weeds since they are not alien) or non-invasive plants for your garden, and remove any invasive ornamentals in your garden. It is usually possible to find visually similar plants to use in place of invasives.   The Garden Smart guide was specifically written to help with this: Both the Native Plant Master Program ( and the Colorado Native Plant Society ( are wonderful resources for people wanting to use more natives in their landscaping.

Ask your local greenhouse and/or nursery to stock more natives. Report any noxious ornamentals to the Department of Agriculture (it is illegal to sell ornamental noxious weeds in Colorado – even if you get seeds by mail order.)  If you do see an invasive ornamental in a seed catalog/website, you can politely and pleasantly inform the company that they need to add “not for sale in CO” to the plant.

Monday, July 25, 2016

When Plants Go (somewhat) Rogue

Posted by: Alison O'Connor, Larimer County Extension

I really enjoy weeding my landscape. Call me crazy, but I enjoy plugging my ears with my iPod, making things tidy and dumping five-gallon buckets of weeds in the trash. It's a real sense of accomplishment. I also enjoy seeing what's new in the garden...did my newly planted perennials survive? Do the shrubs need water? And seeing what's gone rogue.

Uh oh. Plants gone rogue. The potential to be invasive. Plants you want to avoid with a ten foot pole (mint, anyone?). But is "going rogue" a bad thing? In some cases, no....I actually enjoy plants that gently go rogue. Those that randomly pop up and say "Hello! Here I am! Aren't I cute?!" And those that are easily to pull out and remove.

An example of a plant that's gone rogue and is NOT easy to mitigate is Russian sage. Yet I have it in my landscape. CO-Hort blogger Eric discussed this topic a couple years ago (and offers great suggestions to alternatives). But as big of a pain as this plant is, it does have a place...and in my yard, it is a border between my landscape and our neighbor's gravel driveway. It adds some nice separation. It's also a honey bee magnet. But sadly, Russian sage doesn't care about property lines, so I'm constantly pulling it from their gravel. Ugh. Russian sage--a bad rogue plant.
Russian sage growing in my neighbor's gravel pad. You can also see where I whacked it back to stay on our side of the property.
But some examples of gentle roguers (a new word?) include:

Petunia! Maybe this is common for you, but I've never had a petunia reseed. This one took up residence in my flagstone path, which is a great spot. What I'm trying to remember is if the petunia hanging basket I had last year was white? This petunia is so cute!
White petunia that found a home in the flagstone path.
Portulaca! Another annual, and one that commonly reseeds. I planted a few plugs a number of years ago and every year since, the portulaca fills in gaps in the flagstone and nearby beds. Fine by me! It's easy to pull and has great flowers that only are open during the day.
Portulaca that reseeds every year in the flagstone. The only problem is it's hard to distinguish from purslane (they are in the same genus).
Lamb's ear! I feel this may be controversial for some, since lamb's ear is a love it-hate it plant. Personally, I love lamb's ear, and while it's in the mint family and can be invasive, I find it easy to control by ripping it back whenever necessary. But what I find absolutely adorable about this lamb's ear is that this one is in my vegetable garden, a good 20+ feet from where the lamb's ear is planted. I can't bear to remove it, so I'll leave it for awhile and admire its perniciousness.
Lamb's ear roguing it in the veggie garden. So cute! And my garlic (on right) is nearly ready for harvest.
Angelina sedum! I have blogged about how much I love this sedum in past posts, so I won't belabor the point, but this sedum is lime green in summer and copper in fall. And it creeps and fills in. I started with a very small 4" perennial and it's grown to fill in a pretty big spot. I've also found it near my shed, rooted in a path and happily growing wherever it sees fit. Don't like where it's moving? Pull it and replant the roguers.

Maple was so excited to be in this photo with the Angelina sedum.
Coneflower! I feel like this one blindsided me. I guess I should have known, seeing as how coneflower is a native, but wow. Talk about prolific. I'm going to label this one a "medium roguer" since it's not as easy to relocate or remove. I originally planted coneflower in a sunny spot near a path and some other perennials. They quickly grew to be five feet tall and reseeded everywhere. In the path, across the yard and a few other spots. But can you really dislike coneflower? It's sturdy, a great bloomer and a friend to bees. So I deal with it.
The original coneflowers.

This coneflower was not planted, but found a home by the lavender. I like it! 
Sunflowers! And other bird seed! The birds in my yard go crazy for black oilers. So do my beagles for that matter. And if you feed the birds, you'll get some of the seed germinating below or nearby the feeder. It's inevitable. I have sunflowers. You might get corn. Or millet. All of these are annuals that may or may not be your cup of tea. I remove a lot of the sunflowers, but also let a few grow because they are nice.
Why not let these grow? The mulch path is for the dogs, and they provide some obstacles to run around.
Another that just came to mind is columbine...but mine all are tired and sickly-looking, so I'll spare you a photo. So tell me...what in your garden is a gentle roguer? Or even an aggressive roguer that you happen to love? I'm all (lamb's) ears!

Thursday, July 21, 2016

A Lost Hope?

Posted by: Curtis Utley, Jefferson County Plant Diagnostic Clinic

On a recent tree evaluation visit I discovered more fallout from the historic polar vortex freeze event in November 2014. Many of my contemporaries said we would continue to see more damage in otherwise apparently unaffected species and sure enough, now two seasons later, green ash trees are pushing off large sections of damaged bark. 
Bark loss from Callery pear observed in 2015
This damage and the resulting recovery is similar to what we are seeing on ornamental pears but the symptoms have been delayed do to the difference in bark thickness of green ash. The South or Southwest facing sides of green ash trunks and branches had not gone dormant when the freeze event occurred and these portions of the vascular cambium were killed. 
Green ash with loose bark on the south side of the tree.
White ash trees were not affected but green ash trees growing in warm locations, in this particular case street trees growing on a south facing slope show considerable damage. 
Thinning canopy and dieback on ash from the November 2014 polar vortex freeze event.
The marginal cambium that did not freeze is now trying to grow over the damaged section of trunk wood and is pushing the dead bark off in its attempt to close the wound. Another concerning symptom that is explained by this freeze damage is the thinning canopy and decreasing growth increments in affected trees. 
Ash tree attempting to close wounds from freeze injury.
We have had two cool wet springs that should have resulted in fantastic growth in green ash and to see the opposite has had me concerned. The elephant in the room anytime we discuss symptomatic  ash trees is of course the possibility of finding emerald ash borer, especially in trees that are losing chunks of bark, have thinning canopies, and dying crowns. The difference between freeze damage induced bark loss and bark loss as the result of the exotic emerald ash borer is the absence of a zig-zag or meandering pattern visible both on the loose pieces of bark and exposed wood caused by EAB larval feeding. Learn more about emerald ash borer at:
Emerald ash borer feeding (photo courtesy of University of Minnesota Extension)

Monday, July 18, 2016

A Reason For Optimism After Hail

Posted by: Linda Langelo, CSU Horticulture Program Associate, Golden Plains Area
This squash plant emerged after the hailstorm.

We stood and watched two-and-a-half-inch hail devastate the landscape around us within minutes.  All efforts of the growing season gone.  Yet, in the aftermath, there is reason for optimism.  Most vegetables are resilient.  Take the local community garden for example, even the broad-leaved plants in our landscapes most affected can be resilient.  The silver lining is if 50 percent or more of the leaves remaining on the broad-leaved plants, they have the opportunity to produce food for the plant to survive.  Broad-leaved plants such as daylilies can survive.  In fact, at various public places I’ve worked, we intentionally cut the daylilies back after they bloomed then watered and fertilized them.  They produce a second bloom by late August and September.  I don’t recommend this every season.   This is forcing a plant to bloom out of season and not the best cultural practice. 
The native coneflower came through the storm like a champ!
One other optimistic note after a severe storm, is if you have lots of native plants in your garden, it seems that they did better than any of the non-native herbaceous perennials, biennials and annuals.   Amazingly the native plants of the Plant Select™ Program fared the best in the Sedgwick County Courthouse Colorado, landscape. These include:

  • Diascia integerrima ‘P009S’  Coral Canyon Twinspur
  • Penstemon x mexicali 'P008S', Red Rocks Penstemon
  • Clematis scottii, Scotts Sugarbowls that faced the wind and hail head on came through with only a couple of seed heads pruned off the plant.
  • Fallugia paradoxa, Apache Plume
  • Ceroearpus intricatus, Littleleaf Mountain Mahogany
  • Ratibida columnifera, Prairie Coneflower
  • Nepeta “Pskite” PP 18,904 made it through with some tattered leaves as well.
  • Echinacea purpurea, Purple Coneflower also made it through with just a few leaves tattered. 

There are a lot of other natives that would do well, these are just those we can testify to in the hail aftermath.   Natives do not need any fertilization.
Apache plume is tough as nails....what hail?!
There are many methods to heal what is wounded by storm damage; I would suggest the following:

Herbaceous perennials that had prolific flower stalks: prune those back to good growth if there are any good leaves left on the stalks. If there are basal leaves or a rosette at the base of the plant, just prune the stalks to just above the basal leaves or rosette. If the rosette or basal leaves are damaged give a light fertilization.  This will give plant further energy for growing new leaves.   
Master Gardener Joe Stan examining garlic following the hailstorm.
Annuals: you may just have to call it quits, especially if nothing grows back in a week.  Examine them to see if there is anything left to grow and fertilize.  Sometimes with petunias, snapdragons and violas, you may find that they get severely damaged, yet there is still a mass of leaves to grow again and flower.  With the petunias, pruning will be helpful.  Other annuals such as zinnias can be pruned.  There is still enough time in the season.  I am recommending to lightly fertilize annuals once a week. 

On that note, too much nitrogen in the soil increases the mineral salt content.  Excessive salt can dehydrate the plant.  The symptoms would be burning or yellowing of the leaf margins.  The best thing to do is to water and wash the excess nitrogen in the soil.  Nitrogen moves quickly through the soil.  Excess nitrogen will slow root development. 

Our garden of greens following the hail.
Biennials: enjoy what is left because if they are flowering this will be the last year you will see them.  You will need to start over next season.

Shrubs: prune out what is damaged and during the very hot days of summer give them a deep root watering.  The timing for pruning won’t be perfect for some shrubs and you may lose next year’s flower buds. 

Trees: prune out what is damaged and during hot dry periods such as an extended drought give them an extra deep root watering, but do not fertilize them.  It makes sense to remove the branches that are hanging first and make nice clean cuts.  Then examine the tree for any other severe hail damage and prune properly.  Even if your tree looks very thin, give the tree time, it will grow new leaves. 

Fruit trees: remove the damaged fruit.  The damaged fruit will attract pests.  Again, look to see if there are any hanging branches and other severely damaged hail wounds on limbs that might not heal quickly.  Open wounds are an easy entry for pests and diseases for trees and shrubs. 

In answer to the question, “a reason for optimism after hail?” We have witnessed the wounds of severe hail, now we can apply optimism towards what remains on the landscape and heal.  It is hard work, and that, in part, is what gardeners do!

Friday, July 15, 2016

Multi-Site Woody Plant Trial 2006 Planting: Woodward Columnar Juniper

A mature Woodward juniper at the Colorado State University Arboretum 

The Colorado Multi-Site Trial of Woody Plants evaluates the suitability of “new” and underused woody plants across the various climates of the Colorado.  For more information about the trial and test sites see this previous post.  

The 2006 planting of the trial contained a number of interesting plants.  Some of which were very successful  and some which struggled or failed to survive.

The 2006 planting at Harding's Nursery outside of Colorado Springs

2006 Planting:
·       Acer monspessulanum (Montpelier maple)
·       Juniperus scopulorum ‘Woodward’ (Woodward columnar juniper)
·       Larix decidua (European larch)
·       Prunus serrotina (Black cherry)
·       Pyrus ussuriensis ‘Burgundy’ (‘Burgundy’ ussurian pear)
·       Quercus polymorpha (Monterey oak, Netleaf white oak)
·       Quercus undulate (Wavy leaf oak)

One of the plants which is particularly promising based on its performance during the five year trial period is the Woodward columnar juniper.   I know using the word “promising” in the same sentence as “juniper” has caused me to lose credibility with a significant portion of those reading this but hear me out; this is a really worthy plant.  Woodward performed well in the trial and consistently demonstrated both adaptability to our climate and ornamental features which would make it an asset in a variety of landscapes.

Woodward columnar juniper in Fort Collins in the spring of 2016. 

 Woodward was “rediscovered” by Front Range horticulturalists growing at the then defunct Cheyenne Horticultural Field Station.   It is a cultivar of Rocky Mountain juniper selected for its upright habit and strong apical dominance.  As a species, Rocky Mountain juniper (Juniperus scopulorum) is valued as a reliably cold hardy (Zone 3) and drought tolerant conifer.  This bore out with Woodward in the trial.   Across all the sites only a handful of plants did not survive the five year trial.  We observed little winter desiccation, wind burn or pest issues on any of the trial plants.  It is even more notable that we did not observe any damage from snow loading as such damage often plagues woody plants with upright habits.   This may be due to Woodward’s relatively small and shorter lateral branches and strong apical dominance.  The trial plants retained their narrow form and were remarkably consistent in their width across all five planting sites.   More than all this, they were attractive. They had a soft blueish green needle color and a “stately” form.

Mean width data for Juniperus scopulorum 'Woodward' the trial five sites.

Based on the data from the trial it appears Woodward columnar juniper is a tough plant which can be grow successful throughout the state.  Its well suited for small landscapes or tight spaces and could be used as a screen or even as an interesting specimen.  It was promoted by Plant Select in 2015 and was in high demand.  So, if you are interested in planting one get to the nursery early next year!    

Woodward juniper in Orchard Mesa in 2010

Thursday, July 14, 2016

Hoping for a Happy Harvest

Posted by: Sherie Caffey, CSU Extension-Pueblo County Horticulture Coordinator

In my opinion, the best part of growing edibles is reaping the rewards of your labors at harvest time. With a garden full of different fruits, vegetables, and herbs, it can be hard to know when to harvest what. 

Most seed packets have the days to maturity printed on the package. Counting days will provide you with a general guide as to what to expect as far as harvesting goes, but with differing environmental conditions, it is not the most consistent method to use when trying to tell when things are ready for picking.

A better way to guarantee maximum quality produce is to look for signs specific to the plant you are harvesting. Choosing when to harvest is usually a balance between allowing enough time for larger yields, and getting the best freshness and flavor. Here are some things to look for on some common vegetable garden plants:

  • Leaf lettuce can be harvested while young and tender, or midsized. If you harvest leafy greens too large, they will be bitter. Head lettuces and cabbage can be harvested once the head is developed and firm.
  • Tomatoes should be harvested when they reach full color (depends on variety), unless you desire green tomatoes for cooking. You can also pick them when they are just starting to show color and ripen them indoors.
  • Peppers should be harvested when they reach the desired size. For bigger peppers, leave the early ones on the plant, and harvest the later growing peppers while smaller. Similarly, if you want a red pepper instead of a green one, let it mature longer.
  • Summer squash should be picked when the size is typical for the variety, and the skin is tender. Winter squash should have a harder skin that is not easily pierced by your fingernail.
  • If you desire new potatoes for cooking, they can be harvested any time. For full sized potatoes, harvest once the vines die down, and store in a cool, dark place. 
  • Harvest onions once the tops fall down. Once you pull your onions you will want to store them in a mesh bag until the necks have dried out, and then store them similarly to how you would store potatoes. 
  • For optimal flavor, herbs should be harvested before they begin to flower. You can begin harvesting once the plant has enough foliage to maintain growth. It is best to harvest early in the day before it gets too hot, but wait for any morning dew to evaporate. 
You can find harvesting information for many other crops on the CSU Extension website. Have a happy harvest!

Monday, July 11, 2016

Turf Rant: Believe me, it IS an irrigation problem!

Tony Koski, Extension Turf Specialist

The home owner insisted they were "watering enough". Clearly
they are not!
In case you missed my last blog on brown spots in the lawn and Ascochyta a few weeks ago, well, it’s still a problem. If you are seeing these symptoms in your lawn: it’s an irrigation problem. Yes, it’s water! Even if you don’t believe me – and most people (professional turf managers and home owners alike) don’t – trust me, it really, REALLY is an irrigation problem. Repeat after me...

There is an irrigation head in the middle of
that green spot - which is in the middle of that
huge brown spot. Hmmmm...could this be
an irrigation problem?
There is the head...way down in the turf.
Poor head-to-head coverage, heads that aren’t level, heads that are too deep, heads that aren’t turning or are plugged, “shadows” created by trees, shrubs, perennials and other obstructing plants in your landscape. There are so many potential causes of poor water distribution, problems that are magnified when we have hot weather and it doesn’t rain for 1-2 weeks. We have seen every conceivable cause of poor irrigation coverage in the past month, after being reassured by the client that “it can’t be water… it has to be something else”. Well, we were correct and they were wrong. Yes, this is turning into a bit of a rant…intentionally!

Yes, it kinda sorta still works. Water comes out,
but not nearly enough to reach adjacent heads.
Just because "this has never happened until this year" (though it probably did)….or you are watering “enough” or “more than I used to” (maybe, maybe not)…. or “it looks like water is going everywhere” (yes, but not evenly)… or “it’s a new irrigation system” (sorry, no guarantees of anything there)… or yada yada yada…. Well, hopefully you get the gist? If you are seeing spots like this in your lawn (especially if there is a bright green spot in the middle of it, or next to it), it’s a water problem.

Conduct your own informal irrigation audit
by placing containers in your lawn (on the
brown and green spots); collect water for an
entire run time and compare depths.
If you still don’t believe me, place identical containers (Tupperware, pint Mason jars, empty yogurt containers or cat food cans, drinking cups that won’t tip over) on the healthy, green areas of your lawn AND on the not-so-good brown areas the evening before your system is set to irrigate the lawn. In the morning, measure the depth of water in the containers. The depth of water on the brown areas will be less than on the green, healthy turf (that’s a promise). It might only be a difference of 0.1 or 0.2 inches, but that difference in water adds up quickly under summer growing conditions. Those parts of the lawn receiving less water become drought- and heat-stressed sooner and more severely than the adequately watered parts of the lawn. The stressed areas are more susceptible to Ascochyta leaf blight, which turns the grass brown (but doesn’t kill it) – or the grass might just begin going dormant (= brown!).

Your job is then to figure out WHY the coverage is lacking on the stressed areas (station run time, sprinkler spacing, pressure, heads that are broken or plugged or obstructed or too deep, etc.) and remedy the problem. If you can’t figure it out or don’t have the expertise, hire someone who understands irrigation systems to help you. Once fixed, the grass can recover remarkably quickly – but that will depend on how long you have waited to do something about it.
Ascochyta outbreak on 9 June 2016 in Windsor

Turf can recover relatively quickly after the irrigation problem is resolved. This photo taken 2 weeks later (23 June 2016)

Looks even better after another week of recovery! (29 June 2016)

Avoid the temptation to turn your lawn into a rice paddy to speed recovery of the brown areas. Soggy conditions can actually slow down recovery. Simply maintain adequate – but not soggy, mushy, swampy – soil moisture. And hope that the monsoon rains begin soon - though predictions aren’t favorable for a good monsoon season at this point (CAUTION: for weather geeks only).

If you are living in a county that offers the CSU Lawncheck service and would like an on-site consultation (we diagnose the problem, but don't repair irrigation systems!), go here:
There is a fee for this service in those participating counties.

Also, many water suppliers offer irrigation audits (generally free of charge) to homeowners and HOAs. Check with your water supplier to see if it is offered and you qualify.