CO-Horts Blog

Thursday, June 28, 2018

Underused dryland native plants

By Irene Shonle, CSU Extension in Gilpin County

Native plants are becoming more and more popular in landscaping, as people seek to reduce water use, increase habitat for pollinators, and create more of a sense of place. Unfortunately, there’s only a limited palette of plants in nurseries to choose from (hint, talk to your favorite nursery and ask them to carry more native species).  The ones that are out there (such as Penstemons, blanket flower, cacti, serviceberry, currants, and more) are great, but there are many deserving plants that I rarely see offered for sale.  This needs to change, people! 😊

Here are some underused (and possibly hard to find) native plants for dry, sunny situations in Colorado.
Cliffrose (Purshia stansburiana)

Cliffrose (Purshia stansburiana) is a shrub native to the western slope.  It has a profusion of creamy yellow flowers, and they smell delightful.  When I was hiking around Grand Junction during bloom (typically May-June), the air was sweet, and pollinators buzzed.  After they are done blooming, they develop a fun fuzzy seed head reminiscent of Apache plume.  They are also very drought-tolerant -- these should be used way more often in our water-limited gardens.  Alas, they do not do well at elevation, but mountain folks like me can make do with a tough (but slightly less showy) relative called Antelope bitterbrush (Purshia tridentata).
Orchid penstemon (Penstemon secundiflorus)

Side bells or Orchid Penstemon (Penstemon secundiflorus): this spring-blooming penstemon has a gorgeous, large flower that is somewhere between purple and pink.  The flowers all bloom from one side of the plant (hence the name side-bells), but the flowers are large and exotic enough that I think the alternate common name, orchid penstemon, captures the essence of them better.  I have seen everything from bumblebees to swallowtails pollinating them. Even out of bloom, the bluish foliage still looks good in the garden.  For a real treat, pair with showy locoweed, (Oxytropis lambertii).
Plains zinnia (Zinnia grandiflora) is a tough ground cover-like flower.  It loves the heat, and will bloom  from mid-late summer in any dry soil, including dry clay.  It covers itself with golden flowers for a long period – and the fact that it blooms in late summer when many other flowers have called it quits give it bonus points.  It looks great with other late summer flowers or grasses.  It prefers full sun but can take some afternoon shade.  There is a Plant Select selection called “Gold on Blue” that has a rhizomatous growth habit and a bluer foliage.
Cushion buckwheat (Eriogonum ovalifolium)

Cushion buckwheat (Eriogonum ovalifolium): I fell in love with this little buckwheat on that same hike I referenced above with the cliffrose.  It is simply stunning – the perfect little puffballs of flowers look like they are out of a Dr. Seuss book – and they often fade from pinkish to pink as they age. This would be awesome in a dry rock garden setting, or in the front of the border. I have my doubts as to how hardy it would be in the higher elevations, but I would grow it now if I could find the right conditions for it.
Pasque flower (Pulsatilla patens)
And can anyone explain why it is so hard to find plants of our native pasque flower (Pulsatilla (Anemone) patens), whereas the European ones are relatively easy to find?  I don’t think they have very different germination protocols, but perhaps I’m wrong on that. It’s such a fantastic early bloomer (early pollinators love it!) and is very tough.

Monday, June 25, 2018

Time for Rust

Posted by Mary Small, Colorado Master Gardener Program Coordinator

Rust on clippers
You’re probably familiar with rust – the kind like you see here on the grass clippers (right) that were left outside all winter!
Plants get rust too, (although not for the same reason as the clippers) and it is appearing on landscape plants now.

Here’s rust on my Zephirine Drouhin rose (below).  I just had to have this plant with the beautiful, fragrant, pink flowers, few thorns and intriguing name. Since Zephrine is a climber, I planted it next to a 4 foot picket fence, imagining how the canes would spread along its length. This antique rose is classified as a “Bourbon” rose and dates from 1868. In spite of all the positives, it has poor rust resistance.
Rust pustules on rose

Rust is a fungal disease that overwinters on fallen leaf debris and canes.  It infects susceptible roses in moist mild weather when the pustules (that form on leaf undersides and canes) release their spores. The disease is tough to control once the symptoms develop. And since you can clearly see the orange pustules as well as yellow spots on the upper leaf surfaces – it is obviously well underway.

Fortunately, it is primarily an aesthetic problem in our climate. Cultural strategies can help manage it – proper siting, keeping the canopy thinned to promote rapid leaf drying and sanitation (removal of diseased leaves and canes.)

While I’ve had moderate success with the cultural strategies I recently learned about a situation in my neighbor’s yard that might be sabotaging my efforts. For some reason, their sprinkler system ran one weekend day when I happened to be looking out a window. One sprinkler head directly targeted poor Zephrine, along with the lawn. I think a conversation and a sprinkler adjustment will help improve the leaf drying situation!

Rust on hawthorn
Here’s a photo of rust on hawthorn (left). I’m not sure which rust this is, but regardless, the rusts that appear on hawthorn (and related species) are more complex than the one on rose.
These rusts have a two- host life cycle, which starts with the maturation of fungal structures on a juniper host. The spores produced by them in the spring blow to alternate hosts, which includes hawthorn, crabapple, apple and others. Years with mild, humid spring weather will produce a large amount of infections.

Tentacle-like reproductive structures
Symptoms appear as yellow-orange spots on leaf surfaces - as soon as flowering is over. Fruiting structures that look like small tentacles develop on the undersides of the spots. When mature, they produce spores that blow to juniper hosts and cause infection. The rust fungus must have both hosts to complete its life cycle. Under the right conditions, the two hosts can be a mile or more apart and still be infected!
Generally, these rust diseases are most obvious on the deciduous hosts because of the colorful spots and premature defoliation of infected leaves. The best way to manage the disease is to select plant species that have rust resistance. You can also remove one of the alternate host plants – three hundred yards up to 3 miles is the standard recommendation. In a landscape setting this is usually impossible.  Generally, the disease is more of an aesthetic than plant health problem in our area.

Rust on mallow - upper surface
Finally, here’s a rust I found on a weedy mallow hiding between a raised bed and fence. It’s the same rust that infects hollyhocks as they are closely related.  Unfortunately it’s not a health issue for the mallow (rats!), but the disease can prematurely defoliate hollyhocks and make them look just plain ugly later in the season. The fungus overwinters on dead leaf and stem tissue of mallow and hollyhock, so sanitation goes a long way to reduce the inoculum for next year. Guess I better get my weed knife out and get rid of this guy.

Rust pustules on mallow - lower surface

Thursday, June 21, 2018

Lilac Ash Borer

Lilac Ash Borer- Cassey Anderson CSU Extension Adams County

Most of us are aware of the looming menace posed by Emerald Ash Borer to our ash trees along the Front Range in Colorado. However, we do have another pest of our ash trees, the lilac ash borer. Lilac ash borer can, like their name, impact both lilacs and ash trees. They are more of a concern in ash trees.  Fortunately they are usually not lethal to the tree.  Adult borers emerge from trees in the spring then lay egg on the bark .  The larva which develop then burrow into the tree where they spend most of their time in heartwood.  They then overwinter in the tree and emerge as adults the next year.

Pupal Skin Left Behind by Lilac Ash Borer (from CSU Extension Lilac Ash Borer fact sheet)

Distinctive round/melon shaped holes can often be found on the main trunk of the tree. During the spring and early summer it may even be possible to find the final pupal skins of the lilac ash borer left in the trunk as the mature insect emerges. The pupal skin may resemble a wasp. They are not related to wasps but rather are a type of clearwing moth which has some resemblance. 
Lilac Ash Borer Exit Holes

We had a severe wind event here in Adams County this spring and saw one of the unfortunate side effects of a tree that had been riddled with the insect.  While the damage caused by the larvae rarely kills trees because it does not feed extensively in sapwood it does weaken and makes them more prone to failure.   

This tree snapped a foot or so off the ground exposing the larval galleries both new and old from the feeding of the lilac ash borer. These trees had been planted in a very narrow strip between road and sidewalk, were not getting sufficient irrigation if you looked at past growth and the grass growing around the trees, several of the trees also had visible girdling roots which likely compounded their stress.
Lilac Ash Borer Galleries 

Generally speaking stressed trees are more susceptible to damage from lilac ash borer. Ensuring that existing trees are planted correctly, do not have girdling roots, and are watered appropriately can reduce infestations of lilac ash borer.  Treatment for this insect is not the same as treatment as for emerald ash borer. For treatment options and more information please see our fact sheet on lilac ash borer:

Monday, June 18, 2018

Growing Strawberries. Vertically!

Adapted from “Vertical Gardening with Strawberries” by Al Myers and Andy Hough
By: Andie Wommack, Douglas County Extension

Vertical gardening greatly increases the amount of plants you can grow in a small space. In a research project done at the Hidden Mesa Research & Demonstration Orchard, they were able to plant 1,500 strawberries in 25 vertical tubes. This took up approximately 13.3% or less of the space that would’ve been needed to plant them in the ground. The methods discussed here can be scaled up or down depending on your production goals! 

When growing strawberries, regardless of method, you need to consider which type of strawberry you want. The three types considered for this project were:
·      June Bearing: produces a major crop but only in spring, usually in June
·      Everbearing: produces a major crop in June and another in late summer
·      Day Neutral: produces a large flush of fruit in June, slows production for approximately six weeks and then produces a more consistent harvest throughout the remainder of the growing season
It’s important to know what your goals are for growing any plant. Knowing when you want, and potentially how much fruit you want, can help you choose which type of plant you want to grow. “Day Neutral” varieties were planted for this project because they produce throughout most of the growing season.

Two different methods were tried, and both have pros and cons. PVC tubes held more plants, hold their shape, and require less potting soil than the fabric tubes. However, the initial cost is higher if using PVC. Also, because they hold less potting soil, the plants run out of fertilizer much quicker. Fabric tubes cost less and can be watered through the sides if needed. These tubs need significantly more potting soil and tended to lose their shape as the soil settled toward the bottom.

If you want to grow strawberries in vertical tubes, the number of plants you will be able to plant depends on the diameter and height of the tube. A 6” diameter, 5’ tall PVC pipe was predrilled to hold up to 100 plants. Spacing for holes in the PVC pipe is 2.5” between each vertical row and 4” between holes in a row. The holes drilled in the PVC pipe were 1.5” in diameter. In the fabric tubes, there is 4” between each vertical row and 8” between the holes in the row. A 2” horizontal slit was cut in the fabric for each hole. A 12” diameter, 5’ tall tube held about 72-75 plants.

Signs of insufficient
nutrient levels
You will need to provide support for your tubes regardless of the type of tube you use. The fabric tubes used in this project were reinforced at the top and bottom of the tubes with high-tensile fence wire then secured to an overhead support structure with bailing wire. The PVC pipes were also attached to the overhead support structure in a similar manner. These were all in a greenhouse, so if you have your tubes outside in an unprotected area, support may have to be stronger to hold up to wind.

Since potting mix is used in these tubes, they should be treated like a house plant container. This means they should be watered frequently and adequately. A micro-sprinkler was installed above each tube and place on an automatic timer so water percolated down through the tube. Fertilizing is also critical and was done on a weekly basis for the fabric tubes because of the high volume of plants and limited soil quantity. Liquid, foliar, or time-release fertilizers can be used and may alter the fertilizing frequency. You will have plants that die for a variety of reasons, however strawberries produce runners that can be used to replace plants lost. If you are growing your strawberries in a climate-controlled environment you can keep them from year to year if you make sure they are watered throughout the winter and don’t freeze. There are other season-extending methods you can use to try and keep your plants from year to year as well, like a mini hoop house or Agribon row cover cloth to hold in heat and moisture.

Initial costs can be high when purchasing the tubes, plants, and planting media, but once this type of system is set up, it requires a very low amount of maintenance. Weeds will be virtually nonexistent, harvest is easy, and since the strawberries are up off of the ground, there is less cleaning and fungal growth on the fruit which can happen if the fruit gets wet. To reduce costs every season, try to overwinter your plants or collect runners that you can plant and grow during winter to plant again in the spring.

The Hidden Mesa Research & Demonstration Orchard in Franktown, CO planted over 500 varieties of fruits and nuts, along with dozens of types of lavender, herbs, and annual vegetables. Their goal is to explore what food crops can be grown in the Front Range Climate and what cultural methods can be used to overcome the extreme climate challenges here. They also provide options for scalable agriculture, edible landscapes, gardening, and community gardens and orchards.

To learn more about the work being done at Hidden Mesa, please visit:

Wednesday, June 6, 2018

The Buzz on Bees and Wasps

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

Western Yellowjacket
Most people know that bees are good. There are, however, those who are still afraid of bees, and of course those who are afraid of wasps. Surprisingly, many don’t know the difference between the two. Bees are typically not aggressive whereas wasps are more likely to sting. We have many species of both here in Colorado, and they differ in many ways.

We have many wasp species that are social and form colonies. These colonies are small in the Spring, and grow throughout the summer. Most wasps feed on live insects, and are important in balancing out pests like caterpillars. Western Yellowjackets, however, are scavengers and feed only on dead insects and garbage.

Yellowjackets are often mistaken for honeybees, but they are not hairy and are more intensely colored. They usually nest underground and their colonies are not usually seen. The Western Yellowjacket is the most concerning stinging insect in Colorado. They become a nuisance around outdoor picnics and garbage. It is estimated that 90% of Coloradans who believe they have been stung by a bee, were actually stung by a Yellowjacket.

European paper wasp
If you have seen a papery, open celled wasp nest under your eaves, in your gutters, or even your grill, it is probably the nest of the European Paper Wasp. They are more slender-bodied than the Yellowjackets, but some have very similar coloration. They feed on live insects, many of which are pests. The fact that they nest in many locations around homes has increased the incidents of stings associated with this wasp.

If you have a wasp nest on your property, and it is not causing an immediate issue, the best course of action is to wait until fall or winter, when the nest will be abandoned, and safely remove it then. You can also take a proactive approach by sealing all openings that allow access to hollow tubes or similar spaces. Active nests that are a nuisance can be sprayed with an insecticide labeled for use on wasp nests. Spray the nest during late evening when the wasps are not flying and most foragers have returned home for the night. Excluding food sources such as open garbage cans or pet food will deter Yellowjackets. They also make traps that will attract Yellowjackets, these are best used in June when colonies are still establishing.

Honeybee, photo by Lisa Mason
           Bees do not feed on insects, only nectar and pollen. One problem we see with honeybees is swarming on sunny afternoons in May and June. Swarming occurs when a colony gets too big and part of it splits off in search of a new home. This is when you will see a mass of bees gathered on a branch or somewhere similar. If you have a swarm, a beekeeper will gladly come remove it for you so they can get a new colony. You can call the Colorado Swarm Hotline toll free at 1-844-SPY-BEES, (1-844-779-2337). It is not advised to kill or spray a swarm with insecticide or water. The hotline is free and you will usually have a beekeeper come to your aide within an hour or two.

Friday, June 1, 2018

Fireblight running rampant

Posted by Carol O'Meara, Boulder County Extension

Symptoms of Fireblight include browning/blackened leaves
drooping in a classic 'shepherd's crook'

Pulling into my drive, I noticed the Honeycrisp apple tree we love didn’t look quite right.  From a small distance away, wilt was evident around its branches and a sinking feeling settled in my stomach.  Upon closer inspection, my worst fears were confirmed: this tree has fireblight.

To have an apple tree is to risk infection from this deadly disease, one that includes oozing bacteria, curled, brown leaves, inedible fruit, and spreading cankers.  This year, with several hail storms coming just as the tree was in bloom proved fatal.  Temperatures and moisture played a role in the infestation and my tree is entirely engulfed and without hope for recovery.

My tree isn’t alone.  In the past week, samples and emails have been brought to our office by people in similar situations, conversations sound more like support groups, and the disease is everywhere I look.  My mind cues up the dramatic, Hitchcockesque music each time I see another blighted tree.

It’s a banner season for fireblight, a bacterial disease that is especially destructive to apple, pear, quince and crabapple. It attacks in spring, when temperatures reach 65 degrees F and frequent rain occurs.  Bacteria overwintered in cankers on the tree resume activity, multiplying rapidly.  Hail drives the bacteria around and into woody tissues.

Fireblight bacteria moving back into the twigs, blackening the wood
Our wet early summer weather created good conditions for this damaging disease, and masses of bacteria have been forced up through cracks and bark pores to the bark surface, forming a sweet, gummy exudate called bacterial ooze. Insects are pickingd up the bacteria on their bodies and carrying it to opening blossoms where it infects trees. 
Girdling cankers – areas of disease on the wood - eventually develop from branch or blossom infections.  Leaves wilt, darken and curl to form a shepherd’s crook. This gives the tree a fire-scorched appearance, thus the name "fire blight." 

There is no cure for this disease, so prevention is the best solution. Remove and destroy newly infected young twigs as soon as possible, so that your tree doesn’t become the mother ship for disease in the neighborhood.  Do this when no rain is predicted for at least two weeks.  It may be best to leave pruning until winter when the bacteria are not active. In young twigs, make cuts at least 12 inches below the dark, visible edge of infection to avoid slicing into the bacteria. Remove all blighted twigs and cankered branches. Prune larger limbs about 6 to 12 inches below the edge of visible infection.

After each cut, surface sterilize all tools used in pruning. Spray tools with Lysol or dip tools in 70-percent ethyl alcohol, or a 10-percent bleach solution.  Bleach can rust tools, so if you use this to sterilize your pruners, wash them after you’re done and apply a light tool oil to keep them rust-free.

Be on the lookout for apple scab, a fungus that attacks leaves and fruit, which also favors cool, wet weather.  You’ll seeing the rapid spread of this disease across apples and crabapples.  At first, leaves get yellow or dark olive-colored spots, then turn yellow and fall off.  Fruit develops dark, greasy-looking spots that then become sunken. 

The disease overwinters on fallen leaves, so clean the area during fall.  Avoid overhead watering that can splash spores around.