Aspens are great trees for our altitude, weather, soil conditions
One of best indications of true autumn is the golden to lemon-yellow coloring of aspen leaves. We'll travel many miles to see the splendor of the "changing of the leaves" every fall as we have only a few short weeks to enjoy this sudden dramatic blaze of color our higher elevations afford us. Groves of white-trunked beauties seem to rise up from about 5,500 feet in elevation to almost 9,000 feet in splendid majesty.
Aspen trees are one of Mother Nature's true wonders allowing the circle of life to exist in our forests. These trees are rather short-lived by many tree standards, being fast growing to 60 feet and usually found where there is ample water to sustain them. After all, their botanical name is Populus tremuloides for quaking aspen, closely related to our familiar native cottonwood, Populus Fremontii. Aspens increase by means of runners, which grow from the roots. This is very handy for procreation or regeneration when aspen, hardwoods (like oak and Rocky Mountain maples) and needled evergreens or conifers are destroyed in forest fires.
Tiny shoots of evergreens are extremely delicate when first germinating, and must be shaded or will burn in our clear high-mountain atmosphere. Aspen provide that shade as their roots or runners can sprout new trees remaining undamaged by fires, as they grow underground even as the parents are destroyed. The aspen grow rapidly, fed by spring rains and ash provided from the recent fire. Most mountain soils are more acidic, although shallow, as eons of conifers have provided fallen needles creating this acidity. Ash can then compliment and neutralize the soil. Aspen grow well under these conditions, thriving without competition from towering, more massive Engleman, Douglas or Colorado spruce, fir and indigenous ground-hugging junipers (J. communis), mahonias or other ground covers.
As aspen flourish, they provide shade for tender, newly sprouted seeds of the many conifers that perished in the recent holocaust. Their succulent new growth may also provide much-needed food for the many animals that re-enter this recent burn as the once barren landscape begins life anew. Birds find shelter and elk or deer rest in the shade of these statuesque, white-trunked sentinels of mountain life. Ursus americanus, our native black, brown or cinnamon bear uses these aspen as a back-scratcher.
Eventually our aspens age, growing old gracefully with cavities from broken branches which now harbor nesting birds and life-giving squirrels as they race among towering branches, dissecting new pine and spruce cones which, in turn, provides forest duff for new generations or planting seeds in rich soil for even more magnificent conifers.
High winds torment their often-lofty crowns, snapping their brittle trunks in half or blowing them totally over to lie waiting on the soft, needle-covered forest floor. Even then the aspen give life by providing shelter with their now exposed roots to tiny deer mice or shrews. The soil around these uprooted trunks provides a nursery for delicate rue, columbine and velvety moss. Mushrooms appear along the sides of the trunk – blown there from spores. Rare wild orchids and Indian pipes appear after summer rains, their pale bodies nourished by the alchemy of bacteria and decaying wood. This process of degeneration progresses with the Aspen being the fodder for yet another cycle of life.
As the forest recovers, aspen groves begin to shrink, shaded and overtaken by the towering soon-to-be-ancient growth of the many conifers that were allowed to live and thrive because of this fast-growing, beneficial tree. This cycle of the forest, with its cast of thousands would not be possible without the main character, our beloved "Ghost of the Forest," the aspen.
Aspens have found a welcome home in many of our city landscapes. With our colder winters they have ample water and are doing well. There are a few things one should remember though when planting any of these trees. Purchase healthy specimens from a reputable nursery. Know that you never plant "just one" tree as trees are formed from runners and will, in all likelihood, continue to grow more trees as they become established, especially if roots are disturbed or cut.
Aspen roots will grow toward water sources as will cottonwoods, especially if they are not given sufficient water to sustain them by the homeowner. Septic tanks and lines, water mains and pipes are open season to roots of any poplar, and the roots eventually can cause damage. Concrete can be cracked or lifted by these tough, tenacious trees but their cousin, the cottonwood, will do even more damage.
With this in mind, give aspen room to grow and flourish, planting in deep, decent soil amended by copious amounts of organic mulch and occasional feedings of acidifying substances. Keep fertilizer more even, nitrogen, phosphoric acid and potash well balanced. Higher amounts of nitrogen can cause weak, spindly growth. Improper watering can and will cause dieback with valuable new growth becoming stunted. Deep, infrequent watering after the tree is established (eight to 10 years) is a must. Deep, monthly winter watering is imperative to survival. Consider where they are native to the mountains, where winter snow is often measured by feet, not inches. Our snow is often dry requiring seven to 14 inches to equate to one inch of rain.
If your soil is composed of heavy clay or caliche, consider raising the planting area by slightly mounding good topsoil mixed with native soil and mulch. This will allow roots to penetrate the heavier soil gradually. In planting areas where the soil was not broken up or disturbed deeply and out a considerable distance from the planting sight you may notice roots growing near the surface of the soil. This is because the heavy clay inhibits growth by not allowing oxygen around the roots. Leaves give off oxygen. Roots require oxygen to survive. Improper or continuous shallow watering also causes surface tree roots.
If unwanted shoots of poplar trees appear where they are undesired a "sucker killer" should be used as trans-locating chemicals such as "Round-Up or Finale" may cause severe damage to the parent tree or death. Soil sterilants may work quite well in lower desert areas but where we receive heavy downpours this product may leach to other desirable plants causing death, often not immediate.
A grove or group of aspen look especially lovely in spring with random, naturalized plantings of brilliant yellow daffodils at their base or Mahonia repens spreading out like a carpet. Mahonia turn a lovely reddish-orange in fall complementing the stark white with black markings of the aspen.
There is a new lovely daffodil that would be stunning next spring if you like different flower shapes. It's the narcissus "Cassata" which has a flower like a daylily, flat with thick substance in creamy lemon yellow, no trumpet like King Alfred's but with two layers of petals. These narcissus are offered by "White Flower Farm" at 10 for $14 ($1.40 apiece, cheaper than a good hyacinth and just as long lasting). A sprinkling of crocus bulbs, scattered randomly then planted where they fall would brighten any cloudy spring day. Dig a hole with a bulb planter or trowel, putting a little mulch in the bottom, plant the bulb and cover your divot with soil and mulch.
(Kate King is a certified nursery professional and gardening consultant).