by Todd Rutherford
As gardeners in Colorado may well know, our climate and altitude make for challenging growing conditions. This doesn’t mean we are completely immune from invasive exotic plants making an unwelcome home here. We do not have the burden that gardeners in wetter and warmer states may have at stopping the spread of invasive plants, but there are a few species you should be aware of so you can help stop these unwanted guests from gaining a foothold in our landscapes.
Why be concerned about invasive plants? They crowd out native plants, propagate uncontrollably, and may reduce forage for wildlife. Some may have a negative impact on your garden plants. And research suggests that some invasive species may pose dangers to humans through the increased risk of flooding due to damaged waterways, or increased fire danger.
The two worst invasive woody plants for Colorado and the surrounding region are the Russian Olive and the Tamarisk. Russian Olive (Elaeagnus angustifolia), is native to western and central Asia. It was introduced into North America in the latter part of the 1800’s. It is not related to true olive plants (Olea europaea) but its fruit is edible but not very palatable for human consumption. It out competes native plants because its seeds are irresistible to birds which spread the seeds far and wide. The seeds have a low mortality rate, germinate readily in poor soil (it can fix its own nitrogen in its roots), reach maturity quickly and thus outcompete native plants. In Colorado, they often begin setting a foothold in riparian areas, and then spread from there.
Russian Olives invading a wetland in New Mexico.
Tamarisk (Tamarix ramosissima), which is more of a shrub than a tree, similarly starts its spread in the riparian areas of the Colorado and other southwestern states. It has been such a successful invader of wet areas, that it has overtaken huge sections of the rivers of the southwest. However, it is not as tolerant of cold temperatures as is Russian Olive, which restricts its spread to the warmer, lower elevations of the southwest. Tamarisk is tolerant of many soil types, and thrives in full sun. One of the concerns about Tamarisk’s effect on native landscapes is how they out compete native vegetation, altering the nutrient cycles of riparian areas. They also consume large amounts of water, and secrete large amounts of salt, both items further slowing the success of nearby native plants. A massive amount of resources and manpower are being directed at the fight to stop the spread of this plant through the wildlands of the desert southwest.
…the Siberian Elm is “one of, if not the, world’s worst trees…a poor ornamental that does not deserve to be planted anywhere”.
Closer to Denver and the urban areas of Colorado’s front range, there are two trees that are common pests. These are the Siberian Elm (Ulmus pumila), and the Tree of Heaven (Ailanthus altissima). Both of these trees release a profuse amount of seeds, and these seeds are very adept at sprouting in disturbed areas. They proliferate along transportation corridors and abandoned lots. Both trees prefer full sun, but Ailanthus can tolerate some shade allowing it to invade some mature native forests.
Young Ailanthus altissima
Although not directly related, Ailanthus trees (a.k.a. Tree of Heaven) are often mistaken as sumacs. In springtime they produce many flowers that have a foul odor which some say is similar to cat urine. It rapidly out competes other tree species, releasing an allelopathic chemical which inhibits the growth of other plants. Some researchers have extracted this chemical from Ailanthus trees, successfully using it as an herbicide. Not only is this tree toxic to other plants, there have been anecdotal reports of it being slightly toxic to humans and livestock. Ailanthus trees can grow quite rapidly, leading to weak, unstable branches.
Siberian Elms also have structural problems, with many weak or dead branches that can break off in heavy wind. Siberian elms have a short dormancy period which leads to early flowering in spring, and late leaf drop in fall. In Colorado that means they can become dangerously loaded with wet snow in our common heavy spring snowstorms, or the occasional fall snowstorm, leading to heavy branches falling on roofs and vehicles. In addition to the dangers of breaking limbs, the trees do not have a very favorable appearance, with an awkward branching pattern. One doesn’t need to search too long before you find many Siberian elm seedlings sprouting up in unwanted spots in the urban landscape. The sprouts show up in shrub beds where they are difficult to remove by hand and hard to spray with herbicides without damaging neighboring desired plant materials. Siberian elms are susceptible to damage from elm leaf beetles which leave the leaves looking skeletonized, but it doesn’t seem to kill the trees. Notable horticulturalist Michael Dirr says the Siberian Elm is “one of, if not the, world’s worst trees…a poor ornamental that does not deserve to be planted anywhere”.
To be fair, I should mention that some people look favorably upon these four tree species, and say that in Colorado’s high desert climate (that is naturally and predominantly tree-less east of the Rocky Mountains), an invasive tree is better than no tree, especially in urban areas. I would beg to differ, noting that these trees are too difficult to control and remove, to the detriment of native flora and fauna. Please become aware of these invasive trees and be considerate about whether you want to allow these in your landscape.
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
If you’ve not purchased holiday lights in several years, you are in for some surprises next time you head out shopping for new holiday lighting. Recent advances have produced a wave of new and innovative LED lighting that is far more energy efficient than holiday lighting your father or grandfather installed in years past. Many of the new LED holiday light strings are 7 to 8 times more efficient than traditional incandescent light strings. This translates to additional benefits aside from lowered electricity bills: more strings can be safely strung together end-to-end (which may mean a simplified layout of your light display) and there is a lowered fire hazard as the strings do not get as hot as many of the incandescent holiday light bulbs.
One down side to these new types of holiday lights is their higher up-front cost. But if you calculate in the lower operating costs, LED lights are likely to cost you less money in the long run. And as more LED holiday lights are being manufactured, prices have been dropping.
One criticism of LED lights has been the tendency of light from LED bulbs to appear harsh and “cold”. Manufacturers have responded to this issue and are now producing LED holiday lighting that appears “warmer”, like the incandescent lights they are intended to replace.
So this year, consider adding some ‘green’ lights to your holiday decor by choosing energy efficient LED holiday lights.
Here’s a list of pros and cons for LED Holiday lighting:
PROS
Lower energy use / operating cost
Lower heat output (Less fire hazard)
Longer life
More strings can be connected safely (Fewer outlets or extension cords needed)
CONS
Higher purchase cost than incandescent.
Color & “temperature” of light output difference as compared to incandescent
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
You may have heard recent dire reports about the health of bees and butterflies. Whether it’s the declining number of the amazing Monarch Butterfly or the constant reports of “colony collapse disorder” in beehives, these reports are alarming. One of the best and easiest things you can do to help these crucial creatures survive and thrive is to plant the perennials, shrubs and trees in your landscape that will give bees and butterflies the food they depend on. Help these pollinators while creating an inviting outdoor space for yourself. Or, if you are pondering the possibility of updating your landscaping in the near future, let Outdoor Design Group design a bee and butterfly friendly garden for you.
Below are listed several different perennials, shrubs and trees that provide food for bees, butterflies and other pollinators. While I’ve listed several pollinator friendly plants here, there are still many more to choose from. Consult the Xerces Society, a nonprofit organization that protects wildlife through the conservation of invertebrates and their habitat, or your local university extension agent for more suggestions of pollinator friendly plants that will grow well in your area.
Perennials for Butterflies and Bees
Asclepias species. Commonly referred to as the Milkweeds due to their milky sap, there are many species in the Asclepias genus that are utilized by butterflies and bees. Many biologists believe that the decline in the Monarch butterfly population is directly correlated to the increasing use of herbicides used to kill Milkweeds in North America, because Monarch butterflies depend on Milkweeds as food for their larvae. There are many Asclepias species that grow in North America, but two that do well in Colorado are Asclepias tuberosa (showy milkweed) and Asclepias speciosa (butterfly weed). Ht. and Wd. varies depending on species and cultivar, generally 15-60” Ht. x 12-18” Wd.
The Mint Family (Lamiaceae). Many familiar and popular garden plants from the so-called Mint Family are favored by bees. Some of these are culinary sage, Russian sage, mint, basil, rosemary, oregano, thyme, lavender, lamb’s ear, hyssop, lemon balm, and bee balm. Ht. and Wd. varies depending on species and cultivar.
Sedum ‘Autumn Joy’. This tall stone crop flowers in mid to late summer (see photo above), making it a good late-season nectar source for pollinators when many other plants have stopped flowering. 18-24” Ht. x 12-18” Wd.
Datura wrightii Although Sacred Datura may not always be a perennial in all parts of Colorado, depending on the severity of the winter, bees love it’s flowers which emit an amazing scent, so even if it is frost tender and may need to be regrown from seed in colder areas, it is worth it. The bees will thank you. 18-24” Ht. x 6-8’ Wd.
Shrubs for Butterflies and Bees
Buddleia alternifolia ‘Argentea’, Silver Fountain Butterfly Bush. This butterfly bush blooms earlier than the other species and cultivars of Buddleia. This large shrub does well in most soils and sites but doesn’t like its roots to stay wet. 12-15’ Ht. x 10-12’ Wd.
Caryopteris x clandonensis ‘Blue Mist’. Blue Mist Spirea is also in the Mint Family, and is not a true spirea, but has flowers that resemble those of the spirea. It is a hybrid of C. incana x C. mongolica that was created in the 1930’s in England by Arthur Simmonds. There are several cultivars of Caryopteris x clandonensis that are good choices for Colorado and which bees and butterflies (see photo below) love. 3-4’ Ht. x 2-3’ Wd.
Mahonia. This genus has several members whose flowers will delight your winged friends. Mahonia aquifolium is a familiar shrub known as Oregon Grape Holly. It is evergreen, easy to grow and produces edible (but not tasty) berries from the yellow flowers that bees appreciate. 4-6’ Ht. x 4-6’ Wd.
Prunus bessyi, Sand Cherry 4-6’ Ht. x 4-6’ Wd.
Philadelphus lewisii, Cheyenne Mock Orange 5-7’ Ht. x 4-6’ Wd.
Rhus aromatica ssp. Trilobata, Three leaf sumac 3-6’ Ht. x 3-6’ Wd.
Rosa woodsii, Wood’s Rose 3-6’ Ht. x 3-6’ Wd.
Trees for Butterflies and Bees
Tilia cordata, Little Leaf Linden. Linden trees perfume the air in springtime and offer up small yellow flowers (see photo below) for pollinators. I’ve heard that in Eastern Europe, a type of beer is flavored with the linden flowers. 30-50’ Ht. x 25-35’ Wd. (depends on cultivar).
Apple / Crabapples. The Malus genus offers many species and cultivars that are attractive to bees. In fact, if there were no bees, you probably would not get any fruit from your apple trees. Ht. and Wd. varies depending on cultivar.
Prunus armeniaca ‘Moongold’, Moongold Apricot. 15-25’ Ht. x 15-25’ Wd.
Prunus nigra ‘Princess Kay’, Princess Kay Plum 15-20’ Ht. x 10-15’ Wd.
Catalpa speciosa, Western Catalpa 40-60’ Ht. x 30-50’ Wd.
Cercis Canadensis, Eastern Redbud 20-30’ Ht. x 20-30’ Wd.
Crataegus ambigua, Russian Hawthorne 15-25’ Ht. x 20’ Wd.
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
Culinary Sage
Many people may think that low-water gardening and edible plants are mutually exclusive. However, some of the tastiest culinary herbs are perennials that can find a home in your water-wise landscaping. So don’t just grow herbs in your vegetable garden, mix them into your perennial beds. While some of the culinary herbs need more water than extremely xeric plants, some of the best and most popular herbs are fairly drought tolerant, thriving in Colorado’s front-range climate.
Thyme is one commonly used herb that is fantastic when fresh. Even if you don’t intend to cook with fresh thyme, just picking a fresh sprig to crush in your hands, releasing the wonderful aroma, is reason enough to grow this versatile and hardy herb. Lemon thyme (Thymus citriodorus) is a great addition to cooked fish or chicken.
Lavender is one classic herb that loves Colorado’s growing conditions if you amend the soil to make it well-drained. Lavender is not commonly used in most American kitchens, but can be part of some amazing deserts and drinks. The best varieties for Colorado are Lavandula angustifolia ‘Hidcote’, Lavandula angustifolia ‘Munstead’ and Lavandula x intermedia ‘Provence.’
Oregano is perhaps one of the easiest herbs to grow in Colorado. In fact I’ve found that some varieties area so easily grown that they can become invasive due to their ability to re-seed. As with many herbs, some oregano varieties are better suited for cooking than others.
Culinary sage (Salvia officinalis) is more shrub like than the above listed herbs. As with the other herbs (most of which are in the Mint family) culinary sage produces gorgeous flowers that bees and other pollinators go crazy for. Culinary sage’s flowers are a gorgeous purple, blooming profusely in early summer. As with thyme, you may be familiar with its dried version, but fresh sage is much better.
A less drought tolerant group of herbs but that are still hardy and a nice addition to small pockets in flower beds are the chives. Regular chives and garlic chives are easy to grow and provide edible leaves and flowers. Toss in some fresh chive blossoms to your next breakfast egg dish, and you’ve turned an ordinary dish into something extraordinary.
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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