Gardens Galore: Summer Pruning ~ By Karen Brewka

Click on the article headline if you would like to read our entire publication online, in original print format. To leave a comment, click the link at the bottom of this post.

For deciduous trees, there are two times a year when no pruning should ever be done. The first is in the spring when trees and shrubs are pushing out leaves and flowers. All the energy in the plant is concentrated in making new growth. Pruning at this time causes so much stress on the plant, it may not recover. Of course, if you are trying to get rid of a tree, say, a big old poplar, cut it down just as the leaves are coming out. This will help to reduce sprouting from the roots. Another time to leave the trees alone is in the fall when they are busy pushing leaves off and making buds for next year. Again, the tree's energy stores are all needed for this fall work. Very little energy is left over to deal with the stress of pruning.
The best time for pruning is when trees and shrubs are dormant in the winter. But some summer pruning might be required. Follow the three D's: dead, damaged and diseased. Prune to new growth without leaving stubs. The International Society of Arboriculture (ISA) has a great web page illustrating good pruning cuts and guiding people through the process of pruning. Just search for 'ISA pruning'.
Dead and damaged branches are pretty easy to see in the summer. Diseases might be tougher to notice. Black Knot of Cherry looks like hard black lumps on the branches. It affects Schubert Chokecherries, Mayday trees, saskatoons and other trees and shrubs of the cherry family. The hard black lumps are easy to see in the winter but in the summer, the only way you might notice this disease is if the branch above the knot is dead. Prune off the dead branch and the knot and go at least 10 inches into healthy wood. The knot should be burned as it is infectious in the early summer and will continue to send spores off to infect other branches.
Another disease to be on the lookout for is Fireblight. Fireblight cause leaves and flowers to quickly wither, turn brown and black and hang on the trees. All apples, crabapples and trees of the cherry family are susceptible. Fireblight must be controlled by law in Alberta.
Black Aphids, although not a disease, are an insect scourge that can attack just about any tree or shrub. Sometimes, pruning off a branch covered in aphids can help. I found that Wormwood (Artemisia absinthe) is a great biological control. The aphids gather on the wormwood and leave the trees alone. Sometimes they destroy the wormwood, but it is so easy to grow that losing a plant or two is not a problem. I have about five of these plants scattered throughout my yard and they are very effective. Right now, two are covered in black aphids and there is nary an aphid on any of my trees.
If you need help, please call your local certified landscape arborist. We have many great arborists practicing in the foothills and they can help you with any tree problem you might have.
The Valley Neighbors Garden Club welcomes new members. For information call Bea at 403– 933–7131.
The Horticultural Club meets every second Tuesday of the month at 7:30 pm. For information call Sheila at 403–931–3989.