by Todd Rutherford
When it comes to trees in designed landscapes in Colorado, landscape architects and designers don’t have very many species to choose from. With that being said, it might seem heretical to propose that the list of trees to pick from be restricted even further. Specifically, I advocate that large evergreen trees NOT be planted in dense urban areas that experience cold winters, unless they are sufficiently distant from walks and streets located north of such evergreens.
The shadows that large evergreen trees cast can help foster ice patches on walks and roads, compromising the safety and welfare of those who utilize these areas to travel about our towns and cities. If we are going to encourage biking and walking to ease automobile congestion and alleviate environmental impacts, having the safest travel routes we can achieve is a noble goal.
It may be surprising to those who don’t work in the landscape, architecture or planning fields, but many municipalities require that a certain number or percentage of the trees on a landscape plan be evergreen trees. Sometimes these arbitrary requirements restrict designers and architects to squeeze these large winter-shading ice patch-makers into a site where it might be best to avoid them. However, I should mention that some municipalities that I’ve worked with do acknowledge the problem of winter shading from evergreen trees, and they do have instructions in their landscape codes to locate proposed large evergreens away from walks and roads that would be shaded by those evergreens.
I first became aware of the problem of evergreen shadow ice patches as an urban bike commuter in the Denver area. It is frustrating at best, and rather dangerous at worst to encounter a patch of ice on a street during winter time. I have found that often times when biking in the Denver area in winter, the majority of streets can be clear of ice, except for those areas shaded by evergreens that are located just south of walks and streets. But it is not just bikers that would benefit from restricting evergreen trees in urban areas. Walkers and runners would also have an improved level of travel safety due to less icing of their pathways.
An ice patch on a Denver street, from the shadow of a large evergreen tree.
Because the foliage canopy of pine, spruce and fir trees does not drop during winter, melting of snow and ice via solar gain is limited. Deciduous trees, which drop their leaves and allow more sunlight to reach walks and streets, are a better choice in place of evergreens. I acknowledge that evergreen trees are often used for landscape screening. But I question whether this screening is worth it when considering their impact to roads and walks during winter.
Another impact from lost solar gain due to evergreen tree shading is on homes and other buildings. A building that sits in the winter shadow of a large evergreen tree will miss out on solar warmth during a sunny Colorado winter day.
I do realize that in dense urban areas, it’s not just trees that can shade our streets and sidewalks. People need shelter and workspaces, and some of those structures could end up shading streets and cause ice patches. But residents don’t need evergreen trees on their urban lot. I advocate for trees to create shade in summer, visual interest in all seasons, and wildlife habitat. But the choice of tree in tight urban quarters needs to be considered carefully.
Despite the tongue in cheek title of this blog post, evergreen trees can be a wonderful addition to the landscape. I am not actually asking for evergreen trees to be banned from urban areas of Colorado. However it does seem best that in dense urban areas that experience cold winter weather, we should consider restricting evergreen trees to parks and large lots, away from streets and sidewalks where their winter shade will not cause icy travel dangers for walkers, bikers and even cars.
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
Calamagrostis brachytricha, Korean Feather Reed Grass
Calamagrostis brachytricha, aka Korean Feather Reed Grass, is a clump-forming ornamental grass with green leaves and fluffy flower plumes. It is not as well known as its infamous cousin Calmagrostis acutiflora ‘Karl Foerster’, commonly known as Karl Foerster Feather Reed Grass. But Korean Feather Reed Grass really should get more attention, as it is an indispensable option to add wispy texture to planting schemes in part shade conditions.
PLANT STATS
Scientific Name: Calamagrostis brachytricha
Common Name: Korean Feather Reed Grass
Plant Type: Ornamental Grass
Mature Height: 3-4’
Mature Spread: 2-3’
Cold Hardiness Zone: USDA zones 4 – 9 (up to 6,500 ft)
Water Requirement: Medium. Slightly drought tolerant once established, but prefers adequate moisture. Requires regular amounts of water if it is planted in more sun.
Exposure: Part Sun/Shade
Soil: Tolerant of a wide range of soils.
Flower Color & Bloom Time: The feather like flower spikes have a pink tinge when they initially emerge in late summer, and then fade to straw yellow in fall. Compared to Karl Foerster grass, the flowers of Korean Feather seem to be much more misty and gauzy when they first appear which gives the plants a wonderfully diaphanous appearance.
Winter Interest: Gold foliage and flowers.
Disadvantages: May reseed under certain conditions.
Availability and Sizes: This plant seems to be regularly available at retail nurseries around the front range. It is typically sold in 1 gallon or 4″ pots.
Best Features: A large, showy, flowering ornamental grass that can take shady conditions.
Maintenance Tip: Like other ornamental grasses, trim plants down to about 4-6” above the surrounding soil in late winter or early spring, before new growth begins to emerge.
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
Japanese beetle eating an Oenothera flower at the Denver Botanic Gardens.
Gardeners around Colorado’s Front Range are coming face to face with a new foe in our landscapes. Japanese beetles have been a pest for years in U.S. gardens in the east, south and mid-west. It is only relatively recently that the feared invasive pest has made its presence known in Colorado.
The beetles (Popillia japonica) are believed to have entered North America via New Jersey in 1916, probably hitchhiking on ornamental nursery stock from Asia. They are voracious feeders, doing damage to trees, shrubs, perennials, annuals and turf grass. Some of the 300 favorite food plants of the adult Japanese beetles are roses, Virginia creeper, grape vines, raspberries, linden, elm and fruit trees. The sign of their destruction is skeletonized foliage and flower petals that have been devoured. The adult beetles feed during the day, preferring hot and sunny days.
Japanese beetle on a “skeletonized” grape leaf at the Denver Botanic Gardens.
The beetle’s one-year life cycle seems tailor made for a traditional lush turf and shrub landscape. They spend winter underground as a grub, feeding on turf grass roots, creating dead patches in the lawn. In June they begin to emerge as adults ready to feed on the flowers and leaves of plants. The adults can be found feeding on plants as late as September. In addition to feeding on your landscape plants, they might be seen mating on those plants. After mating, females will move to turf grass lawns to dig into the soil to deposit their eggs. After depositing eggs, the females will resume feeding on host plants. The females will return to the lawn to lay more eggs. Up to 60 eggs can be laid by each female beetle during her 4-8 week life span.
Back in the turf grass soil, the eggs will hatch and the Japanese beetle larvae will emerge and move to the grass roots to feed. The larvae are most susceptible to drying out and dying when young if the soil dries out. That is one reason some experts advise against over watering lawns in mid to late summer. The larvae will develop rapidly, causing much damage to the turf grass roots, eventually killing some of the turf grass plants. The larvae feed on the grass roots until the temperature drops below 60 degree F. The larvae move deeper down into the soil to overwinter. Once the soil warms up in spring, the larvae move back up through the soil to resume feeding on the grass roots for about 4 to 6 weeks. After that, they begin to pupate. A couple weeks after pupation, the adults will emerge from the soil to feed on leaves and flowers, mate and start the cycle all over.
The worst damage caused by the Japanese beetles seems to be to lawns, where the larvae can cause dead patches. It appears the damage to shrubs and trees is mostly cosmetic, and will not kill those plants. However, this cosmetic damage can be significant and will upset most gardeners.
Unfortunately there is no magic bullet to control Japanese beetles in your landscape. If you discover them when they first arrive, using manual methods to collect them is a wise choice. Do not crush them, or the chemicals released upon squishing will attract more Japanese beetles to your yard. Try collecting them in a jar of soapy water. Traps are not recommended because they also attract more beetles to your yard. Pesticides may be effective at controlling the beetles. However some systemic pesticides have been linked to death of beneficial pollinating insects such as bees. For more information on the safe use of pesticides and other methods to control Japanese beetles, visit the Colorado State Extension webpage on the subject. Some experts advise the application of grub killing pesticides to lawns to kill the Japanese beetle larvae and keep your turf from being destroyed. The extension does say this about trying to control the larvae of Japanese beetles: “Some cultural practices can limit damage and applied chemical or biological controls may also be useful. However, control of Japanese beetle larvae in a yard will have very little, if any, effect on the number of Japanese beetle adults feeding on trees, shrubs and garden plants. The insect is highly mobile so that problems with adult beetles typically involve insects that have moved a considerable distance.”
As mentioned earlier, dry turf soil during the egg laying season (mostly in June & July) will keep some larvae from surviving to become adults. Some experts recommend drying out your lawn and letting it go dormant during the typical Japanese beetle egg laying time, and resuming watering after the eggs have been layed. This would seem a challenging approach to the problem as most people prefer a green, non-dormant lawn during the time of year when a lush lawn is much desired. The extension service does recommend that keeping lawns well watered after egg laying (and once the older larvae are present and most actively feeding) may help the turf survive root injuries caused by larval feeding.
It would appear that typical xeriscape plants are not usually favored by the beetles. This is yet another reason that a xeric and regionally appropriate landscape design is a good approach to follow in Denver and Colorado in general.
Let’s hope we can keep this exotic and invasive pest at bay, and not let it become an established nuisance.
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
The landscaping on commercial sites may be low on a business owner’s list of priorities for their property. But you should not underestimate the positive influence an attractive landscape can have on potential clients. With this in mind, here is a list of ten issues to consider for choosing the right plants to keep your property’s landscaping looking and functioning at its best.
Non-Invasive
Some very hardy plants would be great choices for commercial landscapes if not for their tendency and ability to invade and spread where they are not wanted. This may happen via seedlings or by creeping rhizomes (horizontal underground stems that can send out new roots and shoots). Luckily, here in Colorado and the Inter-Mountain West, our growing climate is challenging for many invasive plants that have ravaged milder climates in North America. However, there are some plants you should never allow to take root in Colorado due to their invasive nature. For a list of plants see: http://www.invasivespeciesinfo.gov/unitedstates/co.shtml; http://www.ext.colostate.edu/ptlk/2041.html
Blonde Ambition Grama Grass and English Lavender
Disease Resistant
Nobody wants to spend extra money or time dealing with or replacing diseased or dying plants. Avoid choosing plants that are easily susceptible to attack from disease or pests.
Long Lived
Along the same lines of replacing diseased plants prematurely, nobody wants to spend time and money replacing plants that live short lives. The cost of purchasing and installing landscape plants is significant, so it is wise to choose plants that will stand the test of time.
Adaptable to various exposures
The location you are planting on your property may currently be in any degree of exposure from full sun to full shade. But conditions may change in the near future. Will a new building or new trees be placed on the neighboring property? Conversely is a structure or tree slated to come down, creating a new pocket of full sun? Picking plants with higher adaptability to various exposures will ensure success for your landscape.
Adaptable to various soils
The soils in my area are typically heavy in clay with a high (alkaline) pH. This is one more challenge to add to the list of issues that face landscape plants. For best success and longevity, choose plants adapted or adaptable to the soil conditions on your property.
Adaptable to variable moisture levels
You may be familiar with desert plants and you may be familiar with rainforest plants. These two extremes of ecology illustrate the wide variability of climate that plants live in. Your landscape likely falls somewhere in between these extremes. However, even in the most average commercial landscape, we might find wide degrees of moisture and irrigation levels. Having plants that can handle these extremes will help ensure your landscapes do well.
Drought Tolerant
Although nearly all municipalities require automatic landscape irrigation, it is good if the plants you specify for a site are truly drought tolerant.
But on the flip side, some plants that are considered very low water plants may be more difficult to establish on a commercial site due to over watering. Many but not all native plants fall in this category. They are more fussy about soils and drainage. They may need to be ruled out of the “set it, and forget it” situation that many commercial clients may seek. But if you have the time or the staff to work with some very low water plants during their establishment time, they can eventually become great components of your drought tolerant landscaping. The easiest plants to use in your landscape will be adaptable to varying soil moisture levels.
A variety of perennials and shrubs adapted to Colorado’s climate.
Not messy or difficult to maintain
Your maintenance crew has enough on their plate with regular landscape maintenance. There’s no reason to increase their burden and your costs by having messy, difficult plants on your property.
Readily available from nurseries (not rare)
If you lose some of your landscape plants due to accidents, vandalism or bad weather, you will likely want to easily replace the missing vegetation. If the plant that needs to be replaced is hard to find, you might have to resort to replacing it with one that does not match.
Attractive/Interesting/Eye-catching
Attract eyeballs and attention to your business by choosing interesting trees, shrubs and flowering plants. Just as having aesthetically pleasing buildings or signage is good for business, eye-catching vegetation and other landscape elements makes good business sense. Choose Trees and shrubs with notable flowers or good fall color.
A Hawthorne tree in spring bloom.
In Summary
If you are planning a new commercial landscape or taking an assessment of your existing commercial landscape, keep these guidelines in mind. They’ll help you avoid potential problems that might repel clients and customers from your property, rather than inviting them in. An inviting landscape on your commercial property is one of the first steps to achieving business success.
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
Helianthemum nummularium, aka Sunrose or Rockrose, is a semi-woody perennial sub-shrub or ground cover. Sunroses are originally native to the Mediterranean region, but have been in horticultural production for quite some time, with many cultivars available on the market. They are distantly related to daphnes, hibiscus, hollyhocks and okra, among other plants. As the latin genus name suggests (Helianthemum translates to “sun flower”), these plants grow well in sunny, dry locations, but we’ve also had good results with using them in partial shade.
Luckily for us gardeners here in Colorado, this plant also prefers alkaline soil. This low-growing perennial provides a delightful floral display starting in late May. The profuse blooms hover over a thick mass of low branches that carry small, oval shaped leaves. The flower color is available in shades of red, orange, yellow, pink and white. Perfect for a rock garden, sprawling over the edge of a wall, or in a hot and sunny border area. The silver leaved varieties are semi-evergreen in winter.
PLANT STATS
Scientific Name: Helianthemum nummularium
Plant Type: Perennial Groundcover
Mature Height: 8″-12″
Mature Spread: 18”-24″
Cold Hardiness Zone: USDA zones 5 – 9 (up to 6,000 ft). In colder climates, Sunroses may overwinter more successfully with a mulch covering. Silver leaved varieties overwinter better than green leaved ones.
Water Requirement: Drought tolerant once established. Silver leaved varieties are more drought tolerant and establish sooner than green leaved varieties. Seem to be able to take poor soils very well, and we’ve had good luck is slightly wetter soil as well- very adaptable.
Exposure: Full sun to part shade. We’ve actually had good luck using these plants under trees where there was quite a bit of shade, but full sun will produce the most flowers.
Soil: Sunroses prefer dry, alkaline, rocky or sandy, well-drained loam.
Flower Color & Bloom Time: Various colors are available: white, yellow, orange, red and pink. Blooms May to June.
Winter Interest: Evergreen foliage.
Disadvantages: Roots rot easily in poorly drained soil. Plants don’t do well in prolonged wet soil during winter.
Availability and Sizes: This plant seems to be regularly available at retail nurseries around the front range. It is typically sold in 1 gallon or 4″ pots.
Best Features: The many beautiful flowers that cover this plant when in bloom. The evergreen foliage is also charming when the plant is done blooming.
Maintenance Tip: Prune off old, woody growth in spring. After flowering, the plants may be cut back to encourage new growth. Don’t prune after summer; plants must be allowed time to harden off prior to winter. Plants may be divided in spring (prior to flowering) every 4-5 years.
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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