While this is a common recommendation, research has not supported it. Following root loss, unpruned trees seem to respond better than pruned trees. Obviously, any removal of branches will reduce the capacity of the tree to produce food in the leaves. Although the tree will probably lose some branches as a result of the root damage (if the tree survives the trauma), it is best to let the tree decide which ones. Thus, pruning should be limited to hazard reduction at first. Later, after the tree has responded to the damage, further pruning would be in order.
In most U.S. soils, the vast majority of trees' fibrous, absorbing roots are in the top 8 inches of soil. Roots grow where conditions are best for root growth, where water and oxygen are available. When we place fertilizer 12 inches to 18 inches deep in the soil, we are putting it too deep..
Many people envision a large, branching taproot growing deep into the soil. Actually, taproots are very uncommon in mature trees. If taproots do develop, they usually will be forced into horizontal growth when they encounter hard subsoils beneath the surface. The entire root systems of most trees can be found within 3 feet of soil. The spread of the root system however, can be very extensive, often extending 2 to 3 times the spread of the crown.
True, some trees such as maples and birches will "bleed" or lose sap from pruning cuts made early in the spring. This bleeding does not hurt the tree, and the loss of sap is inconsequential. With a few exceptions, most routine pruning can be done anytime of year. The worst time is just as the tree has leafed out in the spring. The best time is when the tree is dormant. To maximize flowering for the following year, prune just after bloom this year.
While topping these trees may reduce the potential hazard at first, they will likely be more dangerous in the future. Topping stimulates growth of twigs below the cuts. Growth of many, vigorous shoots leads to branches with weak attachments. Also decay spreads inside the stubs and branches that were topped. Within 2 to 5 years after topping, the tree will have regained its height, but will be more hazardous than before the topping. Besides, topping makes trees ugly. Alternatives to topping include thinning, cabling, or removal and replacement with a more suitable species.
Research has shown that the common wound dressings do not inhibit decay, do not prevent insect entry and do not bring about faster wound closure. In fact, many of the commonly used dressings slow wound closure.
First of all, trees don't "heal" in the sense that wounds on people heal. Our bodies regenerate tissues in much the same form of the tissues that were removed (to a limited extent). Trees compartmentalize wounds, generating woundwood over the wounded area. Flush cutting removes the "branch collar," creating a larger wound than if the branch were removed outside the collar. Also, it is likely that some of the parent branch tissue will be removed. The spread of decay inside the tree is greater with flush cuts.
Tree establishment is best on unpruned trees. Although pruning the top can reduce the amount of water that evaporates from the leaves, the tree needs a full crown to produce the much-needed food and the plant hormones that induce root growth. The tree will develop a stronger, more extensive root system if it has a fuller crown. Limit pruning at the time of planting to structural training and the removal of damaged branches.
Studies using most common tree wraps have shown that they do not prevent extreme fluctuations in temperature on the bark. In some cases, the temperature extremes are worse. Also, tree wraps have proven quite ineffective in preventing insect entry. In fact, some insects like to burrow under it.
Although it is sometimes necessary to stake trees to keep them upright and allow establishment, there are some adverse effects of staking. Compared to staked trees, unstaked trees tend to develop a more extensive root system and better trunk taper. Allowing a small amount of movement can help root and trunk development. Of course, the worst effect of staking is the possibility of trunk damage from the staking wires or ties. Staking materials usually should be removed after 1 year to avoid "girdling" the tree.