To prune or not to prune that is the question. With the arrival of fall perhaps you’re considering cutting back your overgrown lilac or that evergreen taking up more than its fair share of the sidewalk. Set down the trimmers and walk away. You’re better off raking leaves, flipping mulch, and planting pansies.
Extensive pruning in the fall can have a negative impact due to unpredictable weather.
For example: October begins cool and plants are moving into their dormancy period. You decide to cut your burning bush down by a third. Then we have a warm spell for a couple of weeks. The burning bush starts to bud in response to the haircut and warming weather. Next thing you know we drop to 32° degrees and that new growth gets zapped. Now you have a stressed out burning bush.
Here are a few pointers to avoid pruning faux pas:
Prune shrubs that bloom in the spring within a few weeks after they finish blooming. They set their bud for the following year soon after they bloom. If you prune in the fall you remove flowers for the following spring. http://www.mortonarb.org/trees-plants/tree-and-plant-advice/horticulture-care/pruning-deciduous-shrubs
Prune evergreens either mid summer when they finish their spring growth or in the winter. Do not use electric trimmers if possible. http://www.mortonarb.org/trees-plants/tree-and-plant-advice/horticulture-care/pruning-evergreens
Cut down ornamental grasses early to late winter depending on how much you like their winter structure. I like to cut them down before March so pieces don’t blow around all spring (they’re time consuming to clean up).
Cut back shrub roses in early spring when they are just beginning their first bud. You can take them down to 12 to 18 inches. Give them a light haircut in late fall if they are out of control. (Climbing roses should be trimmed to control shape and trained to go where you want them.) http://extension.illinois.edu/roses/prune.cfm
The best time to prune trees is late winter. Do not top trees this creates physical stress for the tree and a poor branching structure as the tree suckers out from all of the new cuts. http://www.extension.umn.edu/garden/yard-garden/trees-shrubs/pruning-trees-shrubs/
Summer blooming shrubs can generally be pruned in early to late winter. How low you prune them will vary according to the plant and your preferences. http://njaes.rutgers.edu/pubs/fs1221/
Perennials will also vary according to type but here is a good rule of thumb. When they start looking ugly cut them back. If they still look good leave them alone. If they are a woody perennial like Russian Sage cut down to 3 or 4 inches but most perennials can be cut down to the ground. http://www.extension.umn.edu/garden/landscaping/implement/pruning_perennials.html
In general the best way to prune is to pay attention to what the plant and Mother Nature are doing before you start cutting. Happy pruning!