People often call me to ask what kind of tree they should plant. What they don't ask is when to plant it or, more importantly, how to plant it. Timing and proper planting techniques are just as important as selecting that perfect tree for your yard.
Even though the planting bug never hits me until spring, autumn really is a great time to plant most trees. You can plant during the entire dormant season - after the first frost but before the tree leafs out in the spring. Fall planting gives the tree a head start as it grows roots before putting most of its energy into top growth. Oaks are one of the few trees that should be transplanted in the spring as they are especially finicky and have better survival rates if transplanted after their buds swell and begin to break open.
You were probably taught as a child that anytime you transplant a plant, the soil level should remain the same. I remember uprooting bean seedlings in elementary school and observing where the stem turned from green to white, actually transforming from stem tissue to root tissue. The rule of keeping the soil the same depth on the plant is true, but can provide a special problem with trees.
Trees grown in large planting fields sometimes get soil piled around the base due to cultivation practices. When nursery owners, landscapers and researchers realized this, they began to take steps to correct the problem, but it is a slow process. Many of the trees for sale now have soil piled around the base. If you keep the soil at the same level when you plant it, you are burying stem tissue and putting the roots far below the soil surface. Some species, especially maples, will send roots upward to try and compensate, but those roots can wrap around the base of the tree in their search for oxygen. If a root gets all the way around the base, it will girdle and eventually kill the tree.
To prevent planting your tree too deep, cut into the burlap before planting and remove just enough soil from the base of the tree to find the root flare. This is the place where the trunk widens out, and you should find a root that is reaching horizontally in this region. (If you are not sure, look at a mature tree and see the way it widens at the base. Observe the difference between the base of a tree and the base of a telephone pole.) Measure the distance from the bottom of the ball to the root flare. This is how deep your planting hole should be.
If you are planting a tree from a container, there is less concern about the soil level. You still should attempt to find the root flare and plant the tree with the flare at ground level. Look for roots that are wrapping around the base of the tree and cut them to prevent girdling. You also should cut into the outside layer of the roots to encourage them to reach outward, or they may never realize that they are no longer in the pot.
You should water the tree as soon as possible after planting and mulch at least a 3-foot circle around the base of the tree. Mulch will help hold moisture in the soil, reduce temperature fluctuation and keep the weeds and grass down that can compete with the tree for water and nutrients. When mulching, make it look like a doughnut and not like a volcano. Piling mulch around the base of the tree has the same adverse effect as the soil you just worked so hard to remove.
Planting your tree at the right time and using proper techniques will help insure that the tree does just what you want: grow.