Trees for Organic Gardens

By Guy Sternberg
source: http://www.organicgardening.com/feature/0,7518,s1-4-76-983,00.html


Planting a tree can be a deeply satisfying act, a commitment to the future of the place where it will grow. Choose a tree that's native to the region, and your rewards multiply.

Natives are likely to thrive in your conditions with minimal attention after the first two or three years. They provide the food and shelter local wildlife depends on. And you needn't worry about introducing an invasive species like the Russian olive (Elaeagnus angustifolia).

Many natives are trees you're already familiar with. The following six genera, or groups, of North American native trees include a variety of species for different conditions; have interesting foliage, flowers, and bark; and become more beautiful with every passing year.

When thinking about a tree to plant, consider that hundreds of the finest shade and ornamental species evolved right here in North America. They have survived thousands of years of climate extremes, they have reached equilibrium with their environment, and most of them learned long ago how to cope with native pests or they would not still be here. This is truly organic!

MAPLES (Acer)
Features: The brilliant autumn color of our native sugar maple is the gold standard by which all other fall foliage is measured. Luckily, this snow-loving species shares its best attributes with maples in warmer, drier climates. In fact, native maples have adapted to nearly every soil type and watering requirement in North America. For example, the canyon maple in the southwest tolerates dry soil and, along with the more cold-hardy black maple, high pH.

Choices: Maples are naturally found in the Deep South (Florida maple), the southeastern mountains (chalk maple), and exposed midwestern sites (black maple). When you add in our other maple species, these trees comprise one of the most diverse and colorful of all tree genera, with more than 100 species thriving throughout most of the northern hemisphere. Every yard should have at least one native maple.

BIRCHES (Betula)
Features: For many people, the appeal of a birch tree lies in its glowing white bark. Our native birch species have bark that ranges in color from white to rosy brown to a shiny steel gray and exfoliates from the trunk in strips and swirls. Native birches are much better adapted to North America's more stressful climates than imports. A birch under stress, especially from heat or drought, invites a beetle that bores into the wood and eventually kills the tree. And this is particularly a problem for the nonnative birches, which haven't evolved to cope with this insect.

Uses: All birches tolerate wet soils, and most prefer them. The paper birch is among the most winter-hardy of all deciduous trees. Although not especially long-lived as trees go, with adequate moisture and sunlight, and freedom from weed competition, birches can grow very rapidly into highly ornamental shade trees that live for 30 to 40 years.

SUMACS (Rhus)
Features: Sumacs suffer from a bad reputation. Most sumac species clump from their roots, forming thickets that many people perceive as being weedy. This tendency is an adaptation to their natural environment, where they must compete for a space in the sun following fires or other calamities. (This is an advantage, however, if you want a dramatic grouping of a single species.) Worse, many people cannot say sumac without the preface poison (referring to the sap reaction, phytodermatitis, that many people have), yet we have only one toxic species, albeit a very colorful one, and you are unlikely ever to see it unless you wade into its swampy natural habitat. Sumacs are small, often shrubby, and therefore capable of embellishing the tiniest backyards with the most brilliant fall color imaginable.

Uses: Their winter form is artistic, and their flowers and fruits can be striking and long-lasting. Sumacs bring nothing but pleasure in the home garden and are among the easiest of all small trees to grow.

OAKS (Quercus)
Features: The noble oak is generally acclaimed as the national tree of the United States. Tall, stately, and sheltering, oaks can live for centuries. As they are an indispensable source of food and cover for many insects, animals, and birds, planting them invites a diversity of wildlife to your yard. Oak wood is strong and stands up to stormy weather. Thick, leathery leaves filter summer sunlight, making oaks effective shade trees, as well. An old adage says that you plant an oak for your children, but that doesn't mean you will have to wait years to enjoy an oak. The chinkapin oak, for example, can grow as much as 20 feet in 10 years.

Choices: The United States and Canada claim nearly 100 native oak species, a diverse group that ranges from low shrubs to forest giants. There's one for nearly any condition. The willow oak thrives in wet soils, while the black oak likes it very dry. The silverleaf oak takes unbelievable desert heat; the bur oak readily shakes off the cold from Saskatchewan to Quebec. The live oak is evergreen; the swamp chestnut oak has great fall color.

HAWTHORNS (Crataegus)
Features: The hawthorns are some of the toughest little trees in the tree business. Native hawthorns have white or pale yellow flowers in spring, some (Washington hawthorn, in particular) have vivid red color in fall, and almost all get to be only about 30 feet in height. The sweeping branches of the cockspur hawthorn are revealed once winter arrives, and the bright fruits of the green hawthorn make a splendid display until they finally drop or are taken by birds.

Uses: Most species have thorns, so take care to place them where you won't run into them. The thorns, on the other hand, make them desirable habitat for the nesting birds that add so much pleasure to gardening. Hawthorns are in the rose family, along with crabapples, a closely related species to which they bear a resemblance. Hawthorn fruits are edible and taste much like crabapples. Some, such as mayhaw fruits, are made into jelly or wine.

PINES (Pinus)
Features: The scent of pine stands for purity and freshness, or so you'd think from looking at the labels of cleansers and air fresheners. But there's more to appreciate about pine trees than that lab-created imitation aroma. They'll grow in the poorest possible soil, which means you're sure to find one that will take to your land, be it dense clay or porous sand. Most pines are unimpeded by drought; loblolly pine, among others, tolerates wet soil as well. Frequent partners to oaks in the wild, pines have adapted to the coldest and hottest of climates.

Choices: You'll have no trouble finding a pine that suits your garden's size, either. Ponderosa pine and eastern white pine, for instance, reach regal heights, growing up to 100 feet tall, where their aromatic needles sing in the wind. Don't have space for a skyscraping tree? Shore pine and piñon pine top out at a more manageable 20 to 30 feet.