On Gardening/Enhancing Root Growth After Planting

4-28-97

University Park, Pa. -- As we approach the spring planting season, gardeners need to be aware conditions that can affect the success or survival of newly planted trees and shrubs. Anything that reduces or slows growth will increase the chance of plant loss or cause a weakened plant.

The most important factor in plant establishment in the landscape is for the plant to start new root growth into the soil that surrounds the planting site Any factor that slows or limits this root growth is a hazard to the plant. The following suggestions may lessen the chances of plant loss due to restricted root growth during the plant establishment phase.

Remove plastic containers from container-grown plants, and plastic burlap and plastic twine that surround the root system on balled and burlapped plants. Plastic burlap will not breakdown in the soil to allow the roots to grow into the surrounding soil. Some sources suggest that a number of vertical cuts be made in the sides of the plastic burlap covering the root ball. I feel that the remaining portions of such plastic material present a threat to future root development and it should be removed.

The same goes for plastic twine that is often used to secure the burlap wrap on the root ball. This twine will not decompose and if allowed to remain around the trunk of the plant will cut into the bark and girdle the stem as it begins to expand and grow.

Plastic is easy to identify because it will melt when exposed to the heat of an open flame. Organic materials will ignite and burn.

Girdling roots can also be a potential problem for plants. Root restrictions of container-grown plants occur when roots grow in a circular pattern in the bottom of the container or around the sides. This root condition develops when some plants are grown too long in a given container.

Future damage to plant quality caused by girdling roots can be reduced at planting time by disrupting the root pattern. Some commercial landscape contractors recommend that 4 to 6 deep vertical cuts be made in the sides and an "X" be cut across the bottom of the root system. This will cut most of the roots and encourage outward root growth in the soil.

Others suggest a "butterflying" of the root ball to insure that the roots will grow out into the soil. The butterfly method, which involves making a vertical cut from the bottom to halfway up the soil ball, may seem harsh at the time. The cut is made in the center of the bottom of the ball and the root mass is spread or flattened. This technique not only disrupts the root pattern, but allows for shallower planting. Shallow planting can be an important element for success in heavy or slowly drained soils.

I find the next barrier to optimum plant establishment is the lack of water during the first growing season. Granted, most gardeners will water newly set material the day it is planted, and maybe even for a few weeks afterwards. However, a quality root system will only grow into a uniformly moist soil and a soil that is moist all summer.

If the soil surrounding the planting hole is drier than the backfill material around the root system, there will be a gradually movement of water away from the root system. You not only need to keep the soil around the roots moist, but you need to pay close attention to soil moisture in the area to prevent drying of the backfill soil in the planting hole.

A good layer of mulch that covers the backfill soil and extends several feet out past the diameter of the planting hole will be effective in keeping proper levels of moisture around the root zone of newly planted trees and shrubs.

***

**Dr. Nuss is a horticulturist at Penn State. He coordinates all extension horticulture programs. He has bachelor's, master's, and doctoral degrees in ornamental horticulture and has been on the Penn State faculty since 1966.