There are several different reasons to prune a tree, and when to prune a birch tree depends on why you are doing the pruning. When you plant a new tree, prune away any dead or damaged branches, any crossed branches, or any that leave the trunk at an angle of less than 45º. In most regions, you will do this in spring, as that is generally the best time to plant trees.
Prune To Guide Growth and Shape The Tree
Pruning to train and shape a tree’s growth should be done in winter, when the tree is dormant and the absence of leaves allows you a clear view of the shape and arrangement of the branches. When deciding how to shape your tree, consider why you planted it to begin with. Is it intended to screen out an unwanted view? Do you want to be able to walk and sit under it? Or do you want a flower bed with filtered sunlight at its base? If you want a thick tree to screen a view, make cuts just above an outward-facing bud; these are called heading cuts. Heading cuts encourage branching. If you want to be able to walk under the tree, use a process called “limbing up.” Over a span of several years, gradually remove the lower branches of the tree using thinning cuts. A thinning cut removes a branch just above its collar, the swelled region at its base on the branch from which it originates. If you want filtered sunlight beneath the tree, use thinning cuts along the entire height of the tree. Always remove any branches that cross other branches or emerge at less than a 45º angle from their base branch.
Prune to Remove Damage or Unwanted Spreading
Any time a tree is damaged, such as after a storm, broken or damaged branches should be removed as soon as possible at any time of year. Use a thinning-type cut just above the branch collar. Also any branches that overhang a house or are near an overhead utility line should be removed for safety.
Don’t Prune At All
If you have a mature tree with large branches that are near your house or overhead utility lines, don’t prune them yourself. In that situation it’s best to hire a professional arborist who has the specialized training and equipment to do the job safely.