How to Stimulate a Tree's Roots to Grow the Tree

Prune the roots to stimulate growth. Wait until the tree is coming out of dormancy in the late winter to early spring, before buds start to form. The tree needs time to rebound.

Measure the trunk diameter. Multiply that number by five. This is the safe zone for the roots. Do not prune roots within this distance of the trunk. For example, if the tree trunk is 4 feet in diameter, do not prune roots that are within 20 feet of the trunk,

Cut smaller roots on one side of the tree with sharp pruning shears. After six weeks, target the roots on the other side of the tree. This lessens the shock to the tree. New feeder roots will grow between pruning sessions, closer to the tree.

Water the root zone thoroughly. Long, deep soakings are more effective than short waterings. Give the tree more water over the next few years because it will be getting less water through its root system. Check the tree often for signs of drought, such as yellowing leaves.

Fertilize the tree in the later winter of early spring to stimulate root growth. The tree may show signs of needed fertilizer, such as yellowing leaves, dropping leaves or sparse foliage. Feed the tree after watering because the moist soil will lessen injury to the roots and help the fertilizer soak in faster. Use an 18-5-11 fertilizer for the best results. Other options are 16-4-8 and 12-6-6, but they are not as good. Trees with up to a 5-foot-crown radius need 1 lb. of 18-5-11 fertilizer, 1.5 lbs. of 16-4-8 fertilizer or 2 lbs. of 12-6-6. If the crown's radius is 10 feet, give it 5 lbs. of 18-5-11 fertilizer, 6 lbs. of 16-4-8 fertilizer or 8 lbs. of 12-6-6 food. A 20-foot radius needs 21 lbs. of 18-5-11 fertilizer, 24 lbs. of 16-4-8 fertilizer or 31 lbs. of 12-6-6. Give a tree with a 30-foot radius 47 lbs. of 18-5-11 fertilizer, 53 lbs. of 16-4-8 fertilizer or 71 lbs. of 12-6-6.

Spread the fertilizer under the entire canopy, beginning 2 feet from the trunk.