By Robert Cox, Colorado State University Cooperative Extension Agent, Horticulture
Looking for trees that will give a `natural look' to your home landscape?
Pinion pine, ponderosa pine, Rocky Mountain juniper, Douglas-fir, white fir and blue spruce are good choices to achieve the look and feel of the great outdoors right in your backyard. Other trees used occasionally to achieve a natural look include lodgepole, limber and bristlecone pine and Englemann spruce.
Don't assume, however, that all these native species are drought-tolerant. Once established, pinion, ponderosa pine and Rocky Mountain juniper are, but Douglas-fir, white fir, and blue spruce thrive on additional moisture. Consider soil conditions, however, before watering.
All evergreens share some common needs. They benefit from:
Let's take a closer look at the most popular evergreens.
PINION (Pinus edulis) also is called pinyon or nut pine. A slow grower, it is a small pine native in Colorado to drier regions up to 7000 feet. Pinions tolerate drought and alkaline soil, but prefer loose, well-drained soils. They won't appreciate typical Front Range clay.
A pinion's worse-case scenario is to be transplanted into a regularly watered lawn. Remember, pinions come from regions with l0-12 inches of rainfall; the Denver metro area gets 15 inches, plus landscape watering. If such a tree survives transplanting, it soon will become stressed and susceptible to insects and diseases.
Overwatered pinions are particularly susceptible to the pinion pitch mass borer, whose larvae tunnel into the tree trunk leaving masses of sap or "pitch." Pine tip moth larvae also tunnel in and hollow out and destroy new growth tips. Urban pinions, incidentally, rarely form nuts.
PONDEROSA PINE (Pinus ponderosa) also prefers loose, well-drained soils. Almost as drought-tolerant as pinion, it grows faster and larger. It is susceptible to mountain pine and IPS beetles when stressed. Pine tip moth, pine needle scale and giant conifer aphids are additional problems. Consider substituting Austrian pine (Pinus nigra). Similar to ponderosa, except for darker green needles, it is slightly more tolerant of clay soils.
ROCKY MOUNTAIN JUNIPER (Juniperus scopulorum), is slow growing and shows considerable variation in the wild. Its foliage varies from mid-green to blue-or-silver green. Numerous selections are available in local nurseries: Blue Haven, Cologreen, Gray Gleam, Pathfinder and Wichita Blue. These are a few of many varieties. As upright evergreens, Rocky Mountain juniper are susceptible to damage from heavy, wet spring snows. Shake out branches as soon as possible after snowfall. Common pest problems include spider mites, (especially when junipers are in a hot, dry, dusty area), conifer aphids and spittlebugs.
DOUGLAS-FIR (Pseudotsuga menziesii), is a conical evergreen often used as a Christmas tree. It can reach 50 feet in the home landscape. While not a Xeric plant, it can tolerate less water than blue spruce and white fir. Spruce budworm and tussock moth larvae can feed on its needles and damage the tree.
BLUE SPRUCE (Picea pungens), is the Colorado state tree. It does not tolerate drought and should not be used in xeriscapes. Mulch around the tree to help conserve soil moisture.
In the wild, blue spruce colors vary from green and blue-green to silver-green. Selections and grafted varieties are available in nurseries. They include Hoopsii, Moorheim, Thompson and Fat Albert. Pests include spider mites, tussock moth larvae, Cooley gall aphids and giant conifer aphids.
WHITE FIR (Abies concolor), is an attractive tree, similar to blue spruce, but with softer foliage. It requires added water in metro landscapes, and appreciates mulching. A mature tree will be medium-sized and a valuable landscape asset. Aphids are occasional problems.
Photograph courtesy of Judy Sedbrook.
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010