Q. What month is best to start trim Chinese elms ?
Pruning when your tree has the strongest natural defense system will give it the best chance to defend itself against pests and disease. The best time of year to prune is when the tree has the highest reserves and is ready for new growth. This is during late dormancy, before buds begin to form (swell).
In our climate February and March, before new buds break, is usually the best time to prune a shrub or tree. And it's also a good time to study the structure and condition of a tree or shrub, so you can decide how and where to prune.
The worst times to prune are when leaves are forming (because energy reserves are low) and when leaves are falling (because new absorption roots develop then and pruning drains energy that would have gone into their formation).
Other times to refrain from pruning living branches due to possible low energy reserves include: during or after a season of severe drought, if the tree has been pruned harshly in the last few years, and if a massed amount of leaves have been lost due to pests or disease problems. Under such circumstances, it is best to prune in a year or two. But, do remove damaged or dead branches, which can be done at any time as needed.
More information on pruning your tree can be found in our Pruning Guide: http://libguides.nybg.org/c.php?g=655011&p=5556294
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