CO-Horts Blog

Tuesday, July 31, 2018

Is there hope for the landscape after hail?

by Amy Lentz

If you live along the Front Range in Colorado and have not had your yard ravaged by hail this year, you should count yourself lucky! I've been in the vicinity of four hailstorms around Weld and Larimer counties this year...and that's four too many! Hail can wreak havoc on one's landscape and garden. After hail, you might be wondering if your garden is toast or if there is something you can do to save the landscape. Depending on the time of year and the severity of the storm, there may be hope...

Hail forms within strong updrafts of some thunderstorms. As the air in the storm rises, it cools due to drops in pressure and temperature creating a colder air mass at the top of the storm. Ice particles can move upward due to the updraft and collect water as they rise, causing them to grow in size. The newly formed hail stones will swirl around in the upper layers of the storm. However, eventually the storm cannot hold onto the heavy hailstone, gravity takes over and it falls to the ground.

The organization Community Collaborative Rain, Hail & Snow Network (CoCoRaHS for short) has a list of hail facts on their website along with a ton of other great weather information. Here are a few interesting facts about Colorado's affinity for these falling ice balls (you can find the complete list here):
  • Colorado is one of the most hail-prone states in the U.S.
  • The Colorado hail season is April 15 to September 15.
  • Hail occurs more frequently in the lee of the Rockies than anywhere else in North America.
  • Hail also occurs very frequently in the high Colorado mountains during the summer. These stones, however, tend to be small and soft and rarely do damage.
CoCoRaHS also has a database to track the number of hail storms in your area, including the size and location of hail reports. For example, both Larimer and Weld counties have had hail reported on 13 separate dates so far this year. The hail reported ranged in size from that of rice (less than 1/4 inch) to hen egg size (two inches in diameter). The most recent storm occurred just two days ago on July 29th. 

Check hail reports for your county here.

So what should you do if your garden or landscape gets hit by hail? Your trees will show the most damage toward the tops as this is where it takes the most beating. Any leaf area still on the tree will continue to photosynthesize and will likely keep the tree going through the rest of the growing season. The tree should leaf out okay the following year. if the damage was not too great. However, keep in mind that the hail can also do damage to the branches and open up the tree to disease, so hail damaged trees should be monitored for additional stress throughout the season. Similar monitoring should be done with perennials, as well.

The Weld County Extension Demonstration Garden after the June19th hail storm, up to dime-size hail.
The Weld County Extension Demonstration Garden 1 month after the hail storm, recovering nicely.

Depending on the time of year that hail hits your annual flowers, they might have enough time to recover and look nice. In early June, I had several containers of annuals damaged by a severe hail storm (up to quarter sized hail for an extended period of time). Needless to say the plants were shredded, with just a few leaf pieces hanging on for dear life. Upon further inspection, I noticed that there were a few new growth points that looked to be spared. So I waited. It's a good idea to wait a few days (up to a week or so) after hail has damaged you plants before you prune them back. This way you can see where there is hope for regrowth, allowing you to leave that growth on the plant when pruning off dead plant parts.

Quarter-size hail from the June 19th near north Fort Collins.

My lovely containers of petunias, zinnias and coleus after hail on June 19th.

Even though this coleus was shredded, a few growing points are still in tact.

After about a week, I removed the dead portions from these annuals and made sure to keep them well watered and as stress-free as possible over the next month to help them recover. After about 5 weeks, the annuals are recovering well. 

Five weeks after hail damage. If you look close, you can see that the coleus from the last picture is growing again.

Vegetables are tricky, as some will not recover at all after a hail storm, while others might be salvageable. Give it a week and see how they respond. You may need to replant if it's early enough in the season. Row covers and hoop houses can be helpful, along with hard structures to protect the plants. The University of Wyoming has an article with additional tips on how to protect the vegetable garden from hail. That article can be found here.

So don't loose all hope! If it's early enough in the season to get regrowth and if the severity of the hail left some leaf tissue in tact, the plants may be able to recover with time and a little TLC.

 Click here to find more information on how to deal with hail damage in this Planttalk Colorado™ article regarding hail.

Monday, July 23, 2018

Lawn and Order: Special Horticulture Unit

Posted by: Alison O'Connor, Larimer County Extension

"Ripped from the headlines...."

In the landscape management system, irrigation-based offenses are considered especially heinous. Low heads, titled sprinklers and inefficient control clocks are all violations we see on a daily basis. The horticulturists who investigate these vicious landscape crimes work hard to keep water waste to a minimum. These are their stories, as told by compelling photos and video.... [BOM BOM]

Episode 1: The Rock
Episode 1: Putting in new landscaping is a great idea! It adds to your personal enjoyment and should increase your home's value. But putting in new landscaping without taking inventory of where your sprinkler heads are located is a sure way to waste water and get brown spots in your lawn.
Episode 2: The Low Head
Green circles = sprinkler heads!
Episode 2: Low heads are a great way to water a very small circular area in your lawn! The smushed, flattened turf is a great piece of evidence to find a low head as the culprit. Raise 'em up! Make sure the head is up above the surface of the turf.
Episode 3: Drip irrigation springs a leak. I think everyone can agree that while drip irrigation is one of the best ways to use water wisely, when the line breaks or emitters pop off, it's a great way to waste water. Check your drip lines often!
Episode 4: Clogged heads lead to brown spots. Sometimes the cause of the crime seems so obvious, especially when you turn on the sprinklers. The last sprinkler in this video is clogged and spitting out water, leading to the brown spot. Just like drip irrigation, check your heads at least once a month, especially if you run them at night.
Episode 5: The Stuck Head.
Maple the beagle knew it was an irrigation problem!
Episode 5: Seeing green and brown stripes in your lawn? Check to make sure your rotor heads are moving! I had a head in my backyard that would work until it reached one side (see photo with Maple, above). Then it would get stuck and not move again during the cycle. And this horticulturist wondered why the giant brown spot in the turf resulted. (Sometimes even horties need help.)
Episode 6: The Geyser
Episode 6: The geyser. Yeah, sprinklers shouldn't shoot 20 feet straight up in the air. Plus, think of how this completely ruins your water pressure! (Short episode.)
Episode 7: Tilted Heads.
Episode 7: I'm not the best person at understanding physics, but a head pointed at this angle will lead to overspraying and will leave a brown spot directly in front. Heads need to come up perpendicular to the surface of the turf at a 90 degree angle. Making sure your heads pop straight up and down will greatly improve your irrigation efficiency!
Episode 8: While we are all supporters of wildlife, your lawn shouldn't tag-team as a duck pond. Fix the heads!

Thursday, July 19, 2018

Spiders in the Garden

Posted by: Jessica Wong, Master Gardener Coordinator, Broomfield County Extension

Spiders may be one of the most important and abundant biological control agents in our gardens. They are generalist predators that feed almost exclusively on arthropods, including many we consider pests. Spiders will kill as many as 50 times the number of prey they actually eat. And, relax, they are not at all interested in biting humans.
This female wolf spider (Tigrosa helluo) was recently brought into our office by a Broomfield employee. She was about 3 inches long! I released her into our Xeriscape Demonstration Garden where, I'm sure, she is providing effective pest control. Photo credit: Jessica Wong 
Dysdera crocata, commonly known as sowbug killer, woodlouse hunter, and “roly-poly killer.” Photo credit:

Spiders provide pest control, day and night, on the ground, on all above-ground parts of a plant, and even in the air. Wolf spiders (Lycosidae) are excellent hunters of pests on the ground, including ants, earwigs, and caterpillars and grubs found at the soil surface. Sowbug killers (Dysdera crocata) are another ground hunting spider that prey on, you guessed it, sowbugs and pillbugs.
This spider is aptly named bold jumper Phidippus audax. Photo credit: Jessica Wong

Jumping spiders (Salticidae) are small hunters can be found in a variety of habitats, from tree trunks to leaves to under rocks. These small spiders hunt for small prey like mosquitoes, aphids, and midges. Crab spiders (Thomisidae) are ambush predators that can be found waiting for prey on flowers. Orbweavers (Araneidae) are the spiders that spin the familiar vertical webs with concentric rings. They catch anything that flies by, such as winged aphids, wasps, and moths.
Goldenrod crab spiders Misumena vatia can change from white to yellow and back to white for better camouflage. Photo credit: Charley Eiseman, Ohio State University Extension
Banded orb weaver Argiope trifasciata. Photo credit: David Cappaert, Michigan State University,

Spiders can provide the most effective pest control when there are many species present in your garden. To support spiders in your garden you will need to provide habitats for them. Apply a layer of mulch or leaf litter for the ground spiders. Reduce tilling to prevent the disturbance of spider nests and burrows. Intercrop varying height plants to create microclimates and web anchor points. Diversifying your landscape can increase the diversity and abundance of spiders in your garden, which will increase the potential for pest control. By creating abundant habitat for spiders in your garden you will also make it more attractive for them to stay outside rather than come inside your house.
Various groups of spiders occupy different parts of a tree. Figure from Patrick Marc & Alain Canard 1997 “Maintaining spider biodiversity in agroecosystems as a tool in pest control.” Agriculture, Ecosystems and Environment 62:229-235.

I love spiders. Spiders are always welcomed in my garden. I don’t even mind them in my house since they are doing a great job of killing flies and ants. I don’t expect you to love spiders now too, but I hope you at least have a greater appreciation for them in your garden.

Tuesday, July 10, 2018

The Plants of Summer

Posted by: Alison O'Connor, Larimer County Extension

Co-workers and friends often joke about my landscape. By now you realize that I adore my lawn, but the landscape plants don't get much attention. My gardening philosophy is that you have to be tough to survive in my landscape. If you need a lot of attention, water or regular pruning, forget it. I've killed A LOT of plants in my tenure in Colorado, but those that have survived have my greatest respect.

And right now, it's tough to be a plant. It's hot, dry and everyone just feels sluggish--including the gardener. But a few are standing up to neglect and thriving. Let's review them:

False indigo (Baptisia australis)
False indigo: Awesome on every level! This has been planted for about six years and this is the first time I really noticed it bloom. Pale lavender flowers on pea-like foliage. The great thing about this plant is it's right where Maple the beagle stalks the squirrels who are trying to eat from the bird feeder, so it gets a lot of paw traffic and abuse. The flowers fade to hardened chocolate brown "pea pods." I cut it back to the ground in the spring.

Sedums: I have many sedums in my garden, but I couldn't tell you any of their names, except for the lime green 'Angelina' (not pictured) and 'Autumn Joy' (not pictured). But ground cover sedums are tough as nails, love it hot and dry and fill in gaps. I call them "gentle creepers" and are not at all invasive. I don't really like the flowers, so sometimes I clip them off.

Above and Beyond rose
Roses: For those who don't grow roses because of the myth they are too much work, you should try them! Roses are one of the easiest garden plants, especially the shrub types--a spring pruning job and occasional clipping in the summer. There are several introductions that you can try. 'Above and Beyond' (pictured) is a climbing rose from the Bailey Nurseries First Editions series. It had incredible blooms just a few weeks ago and is ready for another flush. It also has clean foliage and sparse thorns. Other roses I love are 'Paint the Town' and 'Sunrise Sunset'. Some of the shrub roses have great fragrance, so be sure to stop and smell them!

Hopflower oregano (Origanum libanoticum)
Hopflower oregano: This is a wonderful ornamental that can serve as a ground cover or a trailing plant over a ledge. I love the unique flowers tipped in purple. It's in full bloom right now and the flowers will persist through most of the fall and winter, turning a straw color. The foliage is dainty, held on wiry stems.

Smoketree (Cotinus coggygria)
Smoketree: These large shrubs/small trees are very noticeable when in full bloom (pictured above). The flowers look like plumes of smoke. It's versatile, as it can be left as a multi-stem shrub, pruned to a single-stem tree or cut back to maintain the height you want. The first few seasons it died back almost to the ground in winter. I also love the obovate leaves, which are slightly waxy. The best purple color will occur in full sun. Mine is planted under a honeylocust.

Lavender (Lavendula angustifolia) and threadleaf coreopsis (Coreopsis verticillata)
Lavender and coreopsis: I have seen a lot of lavender in landscapes, which is great, since it's a wonderfully fragrant, bee-attracting perennial. It also does very well in dry, high pH soils. Whack it back to the ground in the spring and watch it re-grow. There's a new introduction called 'Wee One' that is pretty much the cutest lavender you've ever seen. As for the threadleaf coreopsis, also called tickseed, it's a reliable bloomer and I love the purple-yellow combination. Tickseed is a no-brainer. After it blooms, cut it back for a second flush.

A world record prickly lettuce plant?
Check out this record-setting prickly lettuce that was growing up through the lilacs! It was nearly five feet tall. It's amazing how I can wear blinders in the garden and not notice these things...

Maple the beagle is off to investigate other summer-blooming plants for the garden!

Sunday, July 8, 2018

Be Careful with Crabgrass Pre-Emergent Herbicides

Tony Koski, Extension Turf Specialist

Pre-emergent herbicide injury on a Kentucky bluegrass
home lawn. The herbicide was on a fertilizer carrier, thus
the darker appearance where a higher-than-recommended
rate was applied.
Among the mostly widely used lawn weed control products, pre-emergent herbicides (aka “crabgrass preventers") are generally very safe to use on most turf species. Safe, that is, if applied at the correct rate. Using a spreader without adjusting its setting to apply the correct rate, applying the product with a spreader that isn’t operating properly (plugged, skipping, etc.), applying with excessive overlap, or thinking that “more is better” can cause unintended damage to the desirable turf. In the past few weeks we've seen a greater than normal number of pre-emergent herbicide "oops" on home lawns.

New root growth suppressed by a 
misapplication of a pre-emergent herbicide,
displaying the symptomatic root clubbing.
Pre-emergent herbicides “prevent” annual weeds like crabgrass and foxtail from becoming a problem by killing very young, germinating seeds and seedlings; they don’t sterilize the soil, and they don’t kill seeds in the soil. These herbicides kill the young crabgrass, foxtail, and barnyardgrass seedling by stopping root formation – so the tiny plant can’t take up water and dies from drought stress. The crabgrass preventers used most often on home lawns (by lawn care companies, as well as in do-it-yourself products sold to the homeowner) include pendimethalin (Scotts crabgrass prevention products), prodiamine (sold as Barricade; also in Ferti-Lome, Monterey, Bonide, and Pennington home lawn care products), and dithiopyr (sold as Dimension; also in some Ferti-Lome, Hi-Yield, Bonide, and Pennington homeowner products).

Note the root clubbing (red arrows)
on shallower roots: deeper
roots (green oval) are more normal
in appearance because they are
growing beneath the pre-emergent
herbicide layer.
Misapplication due to poor technique (excessive overlap), using a faulty spreader, and intentional or unintentional application at excessive rates can damage desirable turf by stopping or stunting root production in the spring – when these products are typically applied AND when the grass plant is forming its root system. Damaged roots can’t take up water effectively, resulting in turf that is very drought sensitive. Severely damaged plants die – often in spots in the lawn where there was excessive overlap (as in the photos) – leaving brown strips or spots.

Diagnosing this injury can be tricky. Plants on the border of the dead turf will often display stunted root systems – with roots showing little or no branching and a distinctive “clubbing” at the end of the stunted roots. Because pre-emergent herbicides aren’t very water soluble and tend to remain near the surface of the lawn, deeper roots (maybe only an inch or so deeper; see photo) may grow more normally and not display the clubbing seen on roots growing near the surface. Above-ground, the turf may appear dead or severely thinned in stripes that follow application/overlap patterns. As the turf thins, new leaves formed by the surviving grass plants will be wider/more coarse due to the lack of crowding by adjacent plants (the more dense a turf is, the finer the leaf blades will be). The herbicide-stressed turf may also be more susceptible to diseases like leaf spot and dollar spot.

More subtle above-ground symptoms of
pre-emergent herbicide injury on a Kentucky
bluegrass lawn.
Pre-emergent herbicides can last a long time in the soil (4-6 months) – a good thing for providing season-long weed control. That long residual is a bad thing, however, when a pre-emergent causes turf death from over-application – and the residual effect can be even longer because of the very high rates of application that have killed the grass. This makes it difficult to repair areas by overseeding into them – because the herbicide will kill the young seedlings as they germinate. Creeping grasses (bluegrass, the more rhizomatous tall fescue cultivars, bermudagrass) will grow into the killed areas slowly over the summer. Repair by overseeding may have to wait until fall, when the herbicide has been degraded by soil microbes and other degradation forces in the soil. Worth trying, however, is core cultivation/aeration of the affected areas, followed by overseeding with perennial ryegrass. The seed will germinate below the herbicide “layer” on the surface and has a good chance of surviving and masking the damaged turf.

The take-home message? All herbicides have the potential to harm non-target turf, so always follow the label instructions and apply the product using good technique and well-maintained, properly-calibrated equipment.