Hello Fellow Readers, Last week, we spoke about Early Spring Transplants, and the question of root pruning came up from Brian of Stone Church PA. Great question, Brian. Transplanting is always stressful for plants, especially for the feeder roots, those most responsible for bringing nutrients and water to the plant. But, by pruning roots in advance of a transplant, you’ll markedly help reduce transplant shock. And, you’ll improve survival rates by encouraging the plant to produce new feeder roots within the future root ball to be moved.
The Spading Technique of Root Pruning
One technique is called spading – ideal for smaller trees and shrubs and those not in their current location for more than a few years. Using a sharp spade, cut a circle around the plant as deep as the spade’s depth and just inside the intended root ball. Recall from last week’s column a basic rule of thumb for the proper size of a root ball is eight to twelve inches from the trunk for each inch of the caliper of the tree (the width of the trunk at chest height). So, a two-inch caliper tree should have a sixteen to twenty-four-inch-wide and deep root ball.
Root pruning should be done several months to a year before transplanting and more than a year before moving mature trees. Ideally, it should be done in the fall for spring transplants. That way, the shrub or tree can put energy into new feeder roots over winter without the stress of supporting new plant growth. For plants best transplanted in fall, root pruning in spring can work if you keep the soil moist during the entire growing season. Personally, though, I’d prefer you hold off until fall to root prune and move the plant the following fall to lessen the risk of plant stress. Call me cautious…
The Trenching Method of Root Pruning
The same timing protocol goes for the trenching method. Professionals say digging a trench around a tree is better than the spade technique for mature trees. In fact, for older established trees, spacing out the trenching is wise; say halfway around, then dig further around later in the season.
The trench should be twelve inches wide and twelve inches deep or more for larger trees. Again, dig the trench just inside the intended root ball. Fill the trench with two-parts topsoil mixed with one-part compost to provide a cushy environment for the new feeder roots. Keeping the soil moist is critical for success —Deeply water each time the soil is dry two or three inches below the surface. Before you dig out the transplant, check for a thick web of fibrous feeder roots. If they are scarce, give the baby roots more time.
Brian shared his technique of using thick cardboard or a tarp to move a transplant quickly to its already dug new location. That way, you can forgo a burlap wrap; No lingering with your roots exposed to the drying elements, though. Get her in the ground! Garden Dilemmas? AskMaryStone@gmail.com
Column updated 6/6/2021
Link to a related column titles Reasons to Prune