Trees and shrubs decorate landscapes, provide homes for wildlife and cool and oxygenate the air. They can also pose a danger in areas prone to fire and where they attract pests. Control of tree and shrub-related problems requires avoidance of invasive species and a complete cultural program including proper pruning, insect control and commitment to replacement when plants are too weak to thrive.
Need for Control
Controlling tree and shrub growth is a simple matter; the results of neglect can be expensive and take years to correct. Overgrown trees and shrubs can also pose hazards. Overgrown trees that have two "leaders" (main upward growing branches), branches too close together or growing at severe angles may split in storms. Brush offers shelter for small animals like rabbits, rats and other pests. Shrubs that grow too thickly grow shallow roots along the surface to get more air and light. The resulting weak plants die a section at a time and provide little erosion control. Thick brush and overgrown trees present a fire danger in dry weather.
Trees and shrubs that are not native to the area may also be invasive; they may spread so fast that they choke out other plants. Russian olive and various privets are non-natives that have been designated as invasive in parts of the United States. Gardeners who plant native varieties know that they require less care than exotic varieties. Choose plants based on their adult size, not their size in the nursery. Once a tree or shrub is planted, give it the fertilizer and water it needs to keep it growing steadily and attractively.
Shear evergreens and boxwoods to keep them tidy. Regular removal of suckers keeps lilacs and other spring-flowering shrubs blooming. Pinch growing tips of young trees and shrubs like yews back in spring to promote branching and keep them compact. If a shrub has grown too tall or leggy, it can be rejuvenated by cutting branches back to about 10 inches when the shrub is dormant. Rejuvenation is a rebirth for shrubs like spirea, hydrangea --- even shrub roses --- that have decreased blooms over a period of years.
Pruning should begin when a tree or shrub is planted. A quick pruning to remove wood damaged in transit to the planting site or a trim for shape is often all that is needed to keep a tree or shrub attractive and healthy. Trees should be trained to one leader and crowded or competing branches should be removed to allow light and air into the crown of the tree. Removing branches from the lower part of a tree "raises the crown," promoting air circulation. Remove several older branches each season to help them keep their youthful shape and vigor. Spring-flowering trees and shrubs should be pruned after they bloom. Prune most trees and shrubs in late winter when they are dormant; fall pruning leaves the plant vulnerable to pests. Remove dead or damaged branches promptly to keep healthy wood growing compactly.
When shrubs become too thick, rejuvenate or pull them up. Thin thickets by removing some overgrown shrubs and trimming back others. "Grub up" roots with a shovel to keep honeysuckle and trees like willow and purple plums from popping up again. Burning, herbicides and biological agents may affect surrounding plants; never use them to thin out shrubs.