When and Why to Prune Trees

All pruning is wounding. I tell that to all my clients so we have a base line of what we are doing…surgery on a living organism. This must be highly considered. So having a general understanding of a trees’ life cycle is key.

When is the best time to trim a tree?

Great question to ask, it shows that the potential client cares for their trees.

What kind of tree are we dealing with and what is the over all goal of the surgery?

Trees growth cycles are triggered by the change of the season. There are many variables to bring on change in a tree, much like humans, but we identify them as seasons.

Spring pruning:

If we have and very cold winter, a “winter kill” or “die back” caused by freezing or an early thaw becomes evident in spring and can then be removed from the tree. A thumb print of what is alive and what is dead in a tree is recorded, so that any future “die back” is not likely from the cold winter, but something else which may be causing decline in a tree. Heavy pruning is not advisable. The loss of sap is often too severe and “suckers” or “water sprouts” are encouraged to develop. This may be the goal of the plant, especially if this tree flowers off new growth. Over pruning will cause excessive sap around the wound which may attract bacteria and decay and rotting as a result.

In mid-spring, however new vegetative growth may be trimmed back to develop a finer ramification of branchlets or to encourage flowers and fruit on some tree varieties. Alternatively, flowering wood can be trimmed if more foliage growth is desired. Pruning in late spring has the effect of retarding early summer growth.

Summer pruning- if heavy pruning is done in early summer, “sucker” growing is not so likely to result- the reason being that the “growth curve” determined by the flow of sap in the , is now on the downgrade. With some fruiting varieties, trimming at this time tends to encourage fruiting growing rather than foliage.

An advantage of doing hard pruning toward the end of summer is that the healing capacity of the wood is fairly high at this time and wounds should heal well befor the onset of cool weather. However, a disadvantage that may result is the fact that you’re growing that is encouraged by such cutting may not have enugh time to mature before winter and may suffer die back if there is a cold snap.

Mid to late summer pruning can have a dwarfing effect, as the leaves that are the food manufacturers, are removed and the tree must rely on the stored nutrients to further its growth.

Also, since growth early in the season was made at the expense of food stored the previous autumn, most of the reserves have been used and regrow the, therefore, cannnot be overly vigorous. Furthermore, because of the reduction in foliage at this time, a limited supply is stored the following autumn and this caused new growth to be held in check the following spring.

Another effect of late summer pruning can be observed in the rootsystem. With most trees, there is a period of active root growth in late summer and autumn and the nourishment for this is suppiled from the food manufactured by the top growth that growing season. Because less food was made, the root growth is also less and consequently top growth is limited the following spring. In my opinion this may lead to decline depending on many factors but the biggest would be the amount of top growth taken.

Autumn pruning, any dieback that has occurred through summer can be cut out at this time. However, because winter dieback cannot be anticipated it is sometimes better to leave using the stored food in the tree and will experience a vigorous start in spring. One caution , if you do intend to prune in autumn. With some trees, immediately after leaf fall, there’s is a movement of stored food downward form the branchlets to the heavier branches, trunk and rootsystem. Consequently, if pruning is done before this downward flow, there will be an unnecessary loss of stored food. Sounds bad but is it? Consider the patient, is this a fast growing tree that was planted in the wrong space, likely will need to be replanted sooner rather than later? Or can we suppress its growth by heavy pruning every other year or so?

Winter pruning just as in autumn, winter dieback cannot be anticipated. Severe pruning in early, winter is not so good as healing is not rapid during the dormant months. However, pruning in late winter encourages much vegetative growing and stimulates dormant and adventitious buds to open in spring. If the terminal bud on a tree is trimmmed in late winter, the tree doesn’t have time to reestablish the concentration of auxin in the new terminal bud before spring and the result is that the growing strength is more evenly distributed throughout the tree. Another advantage of late winter pruning is that the food stored in the heavy wood and roots of the tree may be used for growth in spring.

With most trees, there is a period of active root growth in late summer and autumn and the nourishment for this is supplied from the food manufactured by the top growth that growing season. Because less food was made, the root growth is also less, and consequently top growth is limited type following spring.

Trees are complicated just as we are, knowing your trees type and growth habits goes a long way towards a happy, healthy tree.

Speak to a local certified arborist that has experience with the local tree life.

I hope this clarified or sheded some light on this subject to help you find what works for you and your trees.