Trees and Shrubs In the Urban Environment

Nothing beautifies the urban or high-rise landscape like trees and shrubs. They relieve the sometimes sterile look of concrete and brisk, simply, easily, and relatively inexpensively. In the urban environment, however, trees and shrubs often have to be planted in containers or in a raised bed. After oil, you con's plant trees on a concrete sidewalk unless someone provided tree pits. As result, planter boxes may be the only way to provide some greenery, and to soften and enhance the urban environment.

Thriving Despite Hardships

Trees planted in boxes and containers live in a stressful environment. In urban settings they fore more air pollution. In northern climates, the root bolls may freeze (and alternately thaw) because of the small soil mass in which they are planted. In southern and southwestern areas, the soil mass may overheat. Growing room is also on issue--trees and shrubs may become root bound due to the limited amount of soil in the container. Roots can't reach out for food and water the way ground-planted trees can. Finally, winds blowing ground high-rise buildings, especially multiple high-rise complexes, or buildings clinging to the side or perched on top of a hill, tend to hove more velocity than winds at flat areas. Container-grown trees and shrubs often do not tolerate wind because of rapid transpiration and evaporation. (Some trees that thrive in containers, despite the wind, are Honey Locust, Japanese Black Pine, Red Cedar, Russian Olive, Austrian Pine, and White Spruce. Shrubs such as juniper and holly also do well in planters.)

Trees planted in boxes or container seldom hove the size or longevity of trees planted in lawns, natural soil beds, or tree pits. Weekend trees and shrubs are more subject to disease and insert infestation. If not carefully selected and nurtured, potted or plantar grown trees and shrubs will also drop their leaves at least one during the summer. While they con usually survive one leaf drop, they seldom survive two. Even so, container-grown trees and shrubs can survive and be beautiful--provided they receive plenty of tender loving care.

Good Health

With proper forethought, selection, and planting, boxed trees can be beautiful and long lasting. There ore several techniques to help keep plants in containers healthy:

1. Use the largest container possible. The bigger the better. Insulate the inside of the planter with Styrofoam to help prevent rapid soil temperature changes.

2. Use good soil with plenty of organic matter. This will soak up and hold water and maintain the proper pH for the plant you ore using. Adding sand to the soil mix odds density and helps anchor the tree. Generally, don't fertilize the first year. If you must, use diluted liquid fertilizer or slow-release, well balanced fertilizer incorporated into the top foyer of soil.

3. Plant the right type of tree or shrub. Magnolias won't grow well in Alaska and palm trees don't thrive in New Jersey. Honey locust does well in the east as a street tree and adopts well to life in a planter. Oaks, because of their long top roots, do not do well in containers although certain species such as pin oak ore good street trees. Pick a tree or shrub that's native to your area and that can acclimate to container life. Your local horticultural society, county agent, or landscape architect should be able to help.

4. Water regularly and thoroughly. A tree in a planter box has limited water storage capacity. Transpiration on hot day will be just as extensive as for a naturally planted tree, while evaporation may be even greater. Mulch, such as wood chips or cedar nuggets, improves appearance, reduces evaporation, and lowers surface temperatures. As with house plants, don't just look for surface drying. Use a probe (a dry stick will do). Insert it in the soil. If the prove is dry at a depth of nearly six inches, water thoroughly. In hot or windy weather, this may need to be done daily.

5. Feed properly. Due to the unusual amount of water supplied to containerized trees and shrubs, nutrients tend to leach out of the soil. Feed once a month (or more if needed) but lightly with commercially-available feeding toilets using a water injecting root feeder (there ore different toilets for different trees). Inject the water/fertilizer solution ground the perimeter of the container, not in the center of the root moss. Or, use slow release fertilizer sticks. Place them ground the outside of the container; used sparingly, fertilizer sticks will continuously and lightly feed the tree or shrub. Another alternative is high nitrogen fertilizer or organic matter worked into the top foyer of soil.

Don't feed in late fall--you do not want to stimulate new growth just before the tree goes dormant. If the leaves show signs of yellowing, feed immediately but lightly and keep the trees adequately watered without overwatering. Two light feedings ore always safer than one heavy one.

6. Feed it iron. Trees and shrubs often require iron since so much is leached out due to frequent watering. Occasional root feeding with iron chelate available from a garden supply store) will help prevent yellowing and leaf foil in deciduous trees. Apply lightly to the first sign of leaf yellowing.

7. Provide proper drainage. Although watering is vitally important, the containers must be able to drain properly. This may mean boring holes in the bottom. If the containers do not drain, trees and shrubs may be subject to root rot, insect infestation, acid soil, and root freezing. Placing grovel in the bottom of the container will weigh it down and help drainage. Cover the grovel with fine plastic screening before adding the soil.

8. Cultivate the surface soil. This provides not only a pleasant appearance, but allows natural rain and nutrients to penetrate.

Making Containers Work For You

The containers themselves con be a landscape attraction. They are available in a broad array of materials, colors, shapes, and sizes, from concrete to fiberglass. Ceramic or clay pots can be beautiful and allow evaporation and cooling, but are somewhat fragile and should be kept in protected areas. They can be used for minor shrubs and dwarf trees, but are not really suitable for trees because of their limited size and durability. Untreated lumber containers will rot. Treated lumber should be lined with styrofoam sheets, not only for insulation but also for keeping the chemical preservatives away from the roots. In hot, sunny climates, light-colored containers keep the soil mass cooler. Containers may be sheathed in wood that acts as on insulator and can be stained or pointed any hue.

Placed properly, a healthy tree in an adequate container--with good soil--can provide years of beauty at a very reasonable cost.