Kristen - from a post I left on another forum site awhile ago. In it, I was figuring that the grower would repot in late May or Early Jun - in your zone, best time to undertake the root work:
For plants that have not been root-pruned before: With a pruning saw, saw off the bottom 1/3 to 1/2 of the root ball. With a hand-rake (like you use for scratching in the garden soil) or a wooden chopstick, remove all the loose soil. Using a jet of water from the hose and the chopstick, remove the remaining soil - ALL of it. This should be done out of sun and wind to prevent the fine roots from drying. 5 minutes in the sun or wind can kill fine roots & set the tree back a week or more, so keep roots moist as you work. After the soil is removed, remove about 1/2 of the remaining mass of roots with a sharp pruning tool, taking the largest and those growing under the trunk. Stop your pruning cuts just beyond where a smaller root branches off the root you are pruning. Be sure to remove any J-roots, encircling roots, or others with abnormal growth.
The first time you root-prune a tree will be the most difficult & will likely take an hour from start to finish, unless the tree is in larger than a 5 gallon container. When you're satisfied with the work, repot into a soil that you are certain will retain its structure until the next root-pruning/repot. Tree (genetic) vigor will dictate the length of time between repots. The slow growing, less vigorous species will likely go 3-4 years between repots. For these slow growing trees, it is extremely important that soils retain aeration. For these trees, a soil of 2/3 inorganic parts and 1/3 organic (I prefer pine or fir bark) is a good choice. The more vigorous plants that will only go 2 years between repots can be planted in a soil with a higher organic component if you wish, but would still benefit from the 2/3 inorganic mix.
Before you begin the pruning operation, be sure you have the soil & new container ready to go (drain screens in place, etc). The tree should fit loosely inside the walls of the container. Fill the container with soil to the desired ht, mounded in the center, & place tree on the mound. Add soil to cover roots & with the chopstick, work soil into all voids in the roots, eliminating the air pockets and adding soil to the bottom of the basal root-flare. Temporarily securing the tree to the container with twine or small rope, even staking, against movement from wind or being jostled will speed recovery time by preventing breakage of newly forming fine rootage. Place the tree in shade & out of wind until it leafs out and re-establishes in the container.
Most trees treated this way will fully recover within about 4 weeks. By the end of 8 weeks, they will have caught & passed a similar plant, that was allowed to remain in its container, in both development and in vitality
Al
