Do you have a tree or shrub that you’d like to restrain from getting much larger? For the next 3-4 weeks, pruning will be the most effect in reducing the size of woody plants. As we near the Summer Solstice, this year on June 21, we are approaching the midpoint in the growth cycle. This is the time when the days are longest and sunlight is strongest in the northern hemisphere. Woody plants start growing rapidly in early spring using energy that was stored in the roots and branches last fall. By mid-summer, the tree’s resources are being stored in the foliage to support photosynthesis.
So, when we prune at this time, we are removing these resources for growth. This is why summer pruning slows growth. By late summer and fall the nutrients are again being stored in the roots and branches, so pruning removes fewer growth-inducing resources. This is also the reason that fertilizing in late summer and fall is the best time to strengthen a tree or shrub, and support development of the buds that will become next year’s flowers and fruits. Note that solstice pruning of trees and shrubs that bloom in mid to late summer will remove the current year’s bloom and fruiting potential (Bluemist Spirea, Russian Sage, Golden Raintree, Rose of Sharon, Seven Son Flower, etc.)
Incidentally, If you would like to keep certain tall fall-blooming perennials more compact and stocky and less floppy or top-heavy, you can shear them back by a third to a half in late June/early July. This works well for tall asters and goldenrods, Blue Sage (Salvia azurea), Agastache.