New Japanese silk trees, also known as silky acacia or mimosa trees, look like they belong in a tropical setting, but are actually hardy and can survive in most soil types. At maturity, they reach heights of 20 to 25 feet tall. The best conditions for Japanese silk trees are sun to partial shade. In the spring, they boast hot-pink flower clusters. There are two ways to grow Japanese silk trees--as single-stem or multi-stem trees. Prune Japanese silk trees regularly to improve shape and keep as healthy as possible.
Guide the Japanese silk tree into a multi-trunk or single-stem tree when it's young. For a central leader tree, choose the strongest trunk and cut off shoots that compete with it. For a multi-trunk tree, allow many to grow out of the ground.
Lie down at the base of the New Japanese silk tree to see if there is sunlight shining through. If not, thin out the canopy in the spring. Prune last year's growth with shears to five or six buds per stem. Doing so will control the growth and spread of the tree.
Remove branches that are growing downward. Place the cut at the V-shaped connection they share with other wood. This will result in a raised crown appearance, which allows for clearance underneath and improves the tree's form.
Pull seedlings out of the ground below the new Japanese silk tree as soon as they sprout. The goal is to remove them before they develop flowers. The seedlings grow very fast and can amount to hundreds of new trees quickly.
Cut branches that appear to be damaged, weak or diseased. Japanese silk trees are prone to brittle wood. Cut just outside of the collar, which is the thick section of bark at the base of unwanted limbs.