Tips

Planting Trees and Shrubs

Modern construction practices have turned the typical home landscape into a man-made "urban" environment. Urban soils are characterized by the removal of native topsoil, erosion, compaction from heavy construction equipment, altered drainage patterns, and loss of organic material. Compaction limits the ability of the soil to absorb water and nutrients and makes its difficult for roots to expand. The removal of organic matter compounds the problem by reducing the plant's access to oxygen, water and essential elements.

Home gardeners therefore face a struggle to establish plant materials on these severely depleted sites. The commonly accepted planting practice is to amend the soil with organic materials. However, this practice has proven to be unbeneficial, and perhaps harmful, to the plant's ability to adapt to its new environment. Linda Chalker-Scott, an associate professor in ecosystem science at the University of Washington, says: "One of the worst things you can do is to change the soil of the planting hole to anything but the native soil".

The key to a healthy plant is its ability to establish a significant root system. Most roots try to expand laterally, often to a length two to three times greater than the diameter of its crown. This expansion does not take place as readily when the soil in the planting hole is richer than the surrounding native soil.

The best solution is to use a garden fork or spade to loosen the soil in the hole and beyond the drip line of the plant, re-fill the hole with the native soil, then add a two to four inch layer of compost or other organic mulch on top.

Another common mistake is to dig a hole that is too deep and not wide enough. The primary cause of death in trees and shrubs is planting too deep. Chalker-Scott says: "When you look at how deeply roots grow, most don't go much deeper than eighteen inches…The best thing to do is make the hole about twice as wide as the root ball and no deeper than the root ball." The sides of the planting hole should not be dug straight down, but sloping away from the tree or shrub.

Plant the tree or shrub one to four inches above ground level. Loosen the root ball and spread out the roots. Re-fill with the native soil, water-in, and add soil as needed as it settles into the hole. Avoid compaction by not tamping down heavily on the soil. Do not prune any branches or leaves; the plant needs them for photosynthesis to occur. Do not stake trees unless you are concerned with heavy winds or vandalism, and even then the stakes should be removed within the first season and a half.