Late winter or early spring, before new growth begins, is one of the best times to plant most kinds of trees and shrubs. In general, evergreens such as pine, spruce and hemlock can be planted in late summer and early fall, and American holly and evergreen magnolia in mid-to-late spring.

Many of the trees and shrubs available at nurseries and garden centers today have been grown in containers. Most need to be handled in a certain way when planted in the ground, according to specialists.

The roots of a well-grown container plants will almost entirely fill the can, according to James S. Wells, Wells Nusery, Red Bank, N.J. The root ball will be vigorous and complete and there will be a clearly visible surface of roots on the ball when it is removed from the container

Before the plant is planted, it is absolutely essential that the root ball, established and built up so carefully, must be thoroughly broken up.

"If the plant is removed carefully from its container and the root ball left undisturbed and placed into a larger can or hole in the garden, poor result will follow," Wells says.

"The ball must really be broken up, and if necessary, the root services of the container ball should be scarred and scraped with a knife or vigorously banged and bounced on the ground to loosen the roots. If this is roots will grow and enter the ajoining soil). If it is not done, the plant will most likey die (theroots will be confined).

"I believe this is true no matters what plants is involved, and I see no reason why the principle should not be as valid for a 10-year-odl shade tree (that has been growing in a containers) as for a 1-year-old rhododendron."

Dr. Francis R. Gouin, associate professor of ornamental horticulture, Unitversity of Marylnad, has been involved in search of container stock production for the past 14 years.

"I agree 100 per cent with Jim Wells and I have been preaching this same technique for the past 10 years," he says. "Matter of fact, I have gone one step further. When planting container gown plants remove the container by either cutting or inverting and knocking the edge of the container sharply. Next, using a sharp knife or digging spade, cut an 'X' mark across the bottom of the root ball and through one-third of the depth of the root ball."

The roots of container-grown plants that are matted at the bottom or circling around the outside of the root ball should be loosened, cut and removed, says Dr. Richard W. Harvis, University of California horticulturist.

"In freeing the roots at the periphery of the root should be broken away to provide better contact between the rootball and the fill soil."

Wells believes that within the next 25 years at least 95 per cent of all nursery stock will be propagated, raised and sold in containers.