by Todd Rutherford
Green Ash tree killed by Emerald Ash Borer
2013 brought tragic news to urban tree enthusiasts in Colorado. In September 2013 the emerald ash borer was found in Boulder County. This find means that thousands of trees along Colorado’s Front Range could be decimated by this pest. And as Colorado State University Professor of Entomology Whitney Cranshaw tells us, the spread of the emerald ash borer (EAB) is dependent upon human activity. It is likely that EAB came to the United States via humans transporting contaminated wood crates from Asia, and it probably reached Colorado through contaminated firewood.
The emerald ash borer, Agrilus planipennis, is a beetle native to Asia. It is small, about the size of a grain of rice. Being a non-native insect in North America, it has no predators to keep its population in check. And unlike the Ash trees in Asia, our native Ash trees don’t possess the natural insecticides that control EAB. Adult borers eat leaves of Ash trees, then mate and lay eggs in crevices in the bark. The eggs hatch, releasing larvae which burrow beneath the bark, which disrupts the trees nutrient and water supplying layers. The tree becomes riddled with tunnels the larvae leave behind. The larvae then hatch in spring, burrowing their way to the surface, where they repeat the cycle of feeding on the leaves, breeding and laying eggs of new generation. They kill the canopy of the tree, limb by limb, with the entire tree dead in 3-5 years.
Adult EAB on a penny.
Colorado’s department of Agriculture estimates that there are 1.45 million ash trees in just the Denver Metro area alone. The costs to spray so many trees will quickly mount.
Tree and insect experts agree that there is no point in spraying your Ash tree unless the tree is currently infested. “Since most EAB treatments provide control for one year or, at most, two years following application there is no benefit in treating a tree prior to when EAB is present”, Cranshaw writes in a recent report from Colorado State University.
In other words there is no treatment that will stop the EAB from attacking your Ash tree. Spraying before the tree is infested only wastes money and needlessly adds dangerous chemicals to the environment. In fact, many entomologists warn that even spraying an infested tree may have lethal impacts on beneficial insects such as bees and butterflies, and won’t completely rid your tree of EAB, and would probably only buy you a few extra years of life of an infested Ash tree.
If we take a serious look at the situation, spraying at all is mostly a futile and dangerous endeavor. Spraying gives tree care companies extra income but endangers the life of beneficial insects, could possibly have harmful effects on people and is very unlikely to ultimately save your Ash tree. As CSU’s Cranshaw has said, he expects in 5-10 years all Ash trees in the Metro Denver area to be infested by EAB. Furthermore, Cranshaw writes: “Once established at a location emerald ash borer can be expected to survive in the area as long as any ash trees remain. Therefore some management of emerald ash borer will be required for as long as one wishes to maintain the tree”. It is our opinion that a better strategy to dealing with EAB is planning for the eventual replacement of your Ash tree, rather than treating your ash tree with toxic chemicals, year after year.
What can we do to slow the spread of EAB to the rest of Colorado?
1.) Do not transport any ash wood in or out of your area.
2.) Do not plant more Ash trees in Colorado.
If you have an Ash tree, you really should consider planting a replacement tree now. If you are unsure about what type of tree would be a good alternative to Ash, contact your local nursery, arborist, or contact us and we can help you with that decision.
This is the official blog of Outdoor Design Group, Colorado Landscape Architects. For more information about our business and our services, click here.
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by Matt Corrion
Recently I had a client express frustration about his inability to kill the crabgrass weeds in his lawn.
It turns out that what he had was tall fescue rather than crabgrass. Tall fescue is a spreading cool season grass that often appears in lawns. It has a courser texture than bluegrass, and will sometimes “green up” in the spring earlier than the rest of the lawn.
How to Remove Tall Fescue
Crabgrass (left) has smooth leaves that often have small hairs. Fescue (right) has ridges on the leaves.
So here’s the thing about trying to remove it: Selective weed killers that target weeds such as crabgrass will not kill tall fescue.
The only way to remove the tall fescue is to treat it with a non-selective herbicide such as Roundup. This type of weed killer will also kill the lawn that is directly around it. Which means you will need to spot-seed that area, or if you have a lot of fescue you may need to remove the entire lawn and start over with seed or sod.
Should You Remove it at All?
In my lawn, I have clumps of tall fescue but I don’t like to use many chemicals on my lawn. I just leave the clumps in place- they are hardly noticeable once the lawn greens up.
Tall fescue emerging in a bluegrass lawn that is still dormant in early spring.
Fescues are actually pretty highly recommended as lawn grasses- according to the Colorado State University Extension Office a fescue lawn can require up to 50% less water than a bluegrass lawn. In fact, one of the popular sod blends we often specify for the front range is a “90/10 Fescue Bluegrass” blend. That is, 90% fescue and 10% bluegrass.
So before deciding to use a bunch of chemicals on the fescue in your lawn, or doing a major lawn renovation – consider leaving it in place. The fescue can be hardly visible at all from a distance, and may end up saving you money in the long term on watering.
This is the official blog of Outdoor Design Group, Colorado Landscape Architects. For more information about our business and our services, click here.
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by Todd Rutherford
As you are all probably aware, we live in a semi-arid climate in Colorado. Unless you have a landscape comprised entirely of native plants, you need to be cognizant of the occasional need for winter watering to maintain healthy landscape plants. This can be a challenge due to the fluctuating temperatures we experience. And unless you want to re-winterize your irrigation system each time you winter water, you likely will be watering by hand.
Generally speaking, if there has been no natural precipitation for a month and the temperatures have been above normal for your region, trees and shrubs planted within the last year will benefit from receiving supplemental 
water. Only water when the air and soil temperatures are greater than 40 degrees Fahrenheit, with no snow cover. Plants that are on the south or west side of your house are more likely to dry out before those on the east or north. And plants that get reflected heat from buildings, walls and fences or that are in windy sites are more likely to dry out more quickly.
Recently planted deciduous trees are most in danger from winter dry spells. Established trees are somewhat immune from winter drought, unless the dry spell is extreme. If you are uncertain if your tree is established, observe this advice from Colorado State University Extension Service: “Trees generally take one year to establish for each inch of trunk diameter. For example, a two inch diameter (caliper) tree takes a minimum of two years to establish under normal conditions.“ Water the newer and younger trees once a month with 10 gallons of water per each trunk diameter, measured at 6 to 12” above the ground. Let the water soak in slowly to a depth of 12”.
Similarly, recently planted shrubs are more susceptible to dry winter conditions than more established shrubs. For new shrubs, water them with 5 gallons, two times per month. Small established shrubs need 5 gallons once per month. Large established shrubs need about 18 gallons per month.
Newly planted evergreen trees and shrubs are also very sensitive to winter drought, because they don’t drop their leaves or needles so they still are transpiring moisture through the needles all year long. Some arborists recommend misting the leaves/needles with water rather than focusing on the soil. Some of the water will trickle down and get into the soil. Consider doing this 3 times a month for those new evergreens. This should help your evergreens avoid the brown damaged needles that occur during drought stress. Evergreens that need special attention during winter drought are spruce, fir, arborvitae, yew, Oregon grape-holly, boxwood, and Manhattan euonymus.
Obviously, if we receive enough precipitation, no supplemental watering is needed. The rule of thumb here is if snow still covers the ground or if there was a significant snow fall (6” or more) at least once in the last month, you probably don’t need to water that month. But if we have a dry spell and you’ve not properly watered your landscape plants, they may become weakened, making them prone to insects and disease.
If you have a recently planted lawn, consider giving it ½” of water per month during winter dry spells. Established lawns shouldn’t need supplemental watering because bluegrass goes dormant in winter.
Do not neglect to properly mulch all your trees, shrubs and perennials. This will help to keep your plants from further drying out.
Once you have watered your landscape plants, don’t forget to unhook your hose from the hose bib so as to avoid frost damage to the pipes once temperatures drop back down below freezing.
This is the official blog of Outdoor Design Group, Colorado Landscape Architects. For more information about our business and our services, click here.
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by Matt Corrion
Despite the recent rain across Colorado, much of the state remains in a drought.
The watering restrictions that Denver Water put in place for this year remain in place, having gone into effect on April 1st.
You may be aware that watering restrictions mean you can only water two days per week, but how long should you run your lawn sprinklers on those days? Denver Water recently released this chart, which includes recommended watering times for different types of spray irrigation. Note that due to the drought, these watering times have been reduced from their standard recommendations.
This is the official blog of Outdoor Design Group, Colorado Landscape Architects. For more information about our business and our services, click here.
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by Matt Corrion
What a summer we are having- wildfires, heat, and drought. Hopefully you have already renovated your landscaping to make it more adapted to our climate. The old “imported” landscaping look of 
bluegrass and high water-use plants is really showing it wear in this heat.
Assuming you followed most of the suggestions in my spring landscape maintenance tips, you got the summer started on the right foot. This will allow you to relax a little more over the summer to enjoy your landscape and barbecues with family and friends. But with summer is full swing and the west abound in hot temperatures, there are a few important landscape maintenance tasks that you will want to keep up with.
Key Dates / Weather Considerations
- The month of July: July is Colorado’s hottest and driest month. Take a look at the bar chart below showing the spike in temperature during July. This means that watering will need to be increased for bluegrass lawns and even many of the xeriscape plants.
- On average, we also actually see a spike in precipitation in July. But this is usually due to large afternoon storms, rather than consistent rainfall. We may go 2 weeks with 100 degree temperatures and no rainfall. Then there may be afternoon monsoon storms for 3 days in a row. It is important to monitor the moisture that your plants are receiving, but also watch for flooding and erosion that can occur in bed areas, and around walls, patios, and other hardscapes from these large storms.
- Hail can also be a factor (fingers crossed that it won’t), although I have found that the more native and regionally adapted the landscape is, the more it can recover from being decimated by hail. Plants seem to have evolved to expect hail in this region of the country.
Trees and Shrubs
- Monitor soil moisture. Provide supplemental watering and/or increase watering times on your drip irrigation system during hot, dry periods.
- Watch for pests and manage them accordingly, as many insects will attack plants when they are under stress from drought.
- Assess which of your plants are under stress from the heat- Consider moving plants that prefer more moisture and shade to a different, more shady location so they will be happier next year. But don’t do any transplanting now, it’s too hot- wait until late August at the earliest.
Perennials and Ornamental Grasses
- Ornamental grasses do not need much care during this period. Most of them should be thriving right now- enjoy the beauty, movement, and texture that they provide!
- Some perennials that are done flowering can be dead-headed to promote another round of flowers!
- Watch soil moisture closely, and add additional mulch around the base of plants if mulch has thinned out. This keeps the roots cool and helps preserve soil moisture.
Lawns
- Hopefully you have followed the 7 Principles of Xeriscape, and have limited your turf areas to those places that are most practical. This is the season where it really pays off (in improved aesthetics, reduced maintenance, and lower water bills).
- You will probably have to increase watering during the middle of summer. However, keep in mind that many turf grasses such as bluegrass will go dormant (the lawn will turn brown) if not extensively watered. This does not mean that the lawn is dead. It has simply gone dormant, and will green back up when temperatures cool and it receives more rainfall.
- Some weed species can be a problem in lawns during mid-summer, especially if the lawn has gone dormant or partially dormant- the weeds do not have much competition. Consider using weed control products and herbicides. Always handle these products carefully, and consider organic options if they are available.
Planting Beds
- Weeding is important during the summer months. Small weeds can easily be pulled, but if they are let go for several weeks they will grow fast in the warm temperatures, making the job much more difficult. It can be pretty easy, and even enjoyable. Just grab a glass of wine in one hand, and stroll through your garden pulling the small weeds before they get out of hand.
Other
- Protect your bees, butterflies, and hummingbirds. Bees will be abundant on your flowering plants- in many areas of the country bees are disappearing, so be sure not to use pesticides on any areas that my impact your bees!
While spring and fall are probably the most critical seasons for landscape maintenance, summer is a time to relax and enjoy your landscape while trying to keep cool. If you spend a few evenings or cool mornings following some of these summer landscape tips, you will achieve piece of mind and your landscaping will be in great shape.
This is the official blog of Outdoor Design Group, Colorado Landscape Architects. For more information about our business and our services, click here.
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