Can I prune my cherry tree if it's in full bloom?
Q: I missed pruning my cherry tree when it was dormant, and now it’s in full bloom. Is it too late to prune?
A: No, it is not too late to prune your cherry tree this year in fact you may have saved its life by not pruning during the wet winter months.
While wintertime is considered the traditional time to prune deciduous trees, there are some trees that are better pruned during the summer months due to the risk of disease that can enter the tree during the wet season. This is true for cherry, apricots and a few related species. With these trees pruning should be done during the summer growing season to keep the tree size in check and avoid disease problems.
Pruning these trees during the winter can lead to detrimental fungal and bacterial canker diseases, including Eutypa dieback, Botryosphaeria canker and bacterial canker. Disease pathogens can be spread by rain or tree wounds, such as pruning wounds, during wet weather; causing infections to spread through the wood. If this happens for several years, it may eventually kill the tree.
For trees that are infected with these diseases, their twigs, limbs or the entire tree will wilt and die suddenly in late spring or summer with the leaves still attached. Bark may be darkly discolored and amber-colored gumming may ooze. If you cut into the branch you will see infected areas in the interior of the wood that are discolored brown, sometimes in wedge shapes. Trees infected with the bacterial canker disease will show a cambial area on the limb that will turn red or speckled red and then brown.
If you suspect that you have one of these disease on your tree, remove the infected branch by cutting at least one foot below any internal symptom of the disease, preferably during the dry season when the risk of spreading the infection is lowest.
To avoid disease problems, gardeners should not prune apricots and cherry trees during the typical rainy period from September through mid-April. Later rains can still lead to infections although tissue susceptibility to these diseases decrease with warmer weather. If growth is very vigorous, the first summer pruning can be done in late May or early June, at which time many strong upright shoots can be removed to allow sunlight to reach lower fruiting branches.
However, the main or final pruning should be done in August after the tree has finished fruiting, for some species of apricots.
More master gardener columns:
When doing heavy pruning, especially at that time of year, be careful to not remove more than one third of the overall canopy. Removing too much growth may lead to sunburned branches, so leave spurs and some other shoots to provide some shade to main tree limbs. It’s also good practice to whitewash west- and south-facing branches with a 50:50 mixture of interior white latex paint and water to prevent sun burning, or use a tree wrap.
The Shasta Master Gardeners Program can be reached by phone at 242-2219 or email email@example.com. The gardener office is staffed by volunteers trained by the University of California to answer gardeners' questions using information based on scientific research.