By Robin Haglund
In reality, the opposite is true, especially in locations that endure winter freezes. Almost all pruning should take place much earlier in the season and wrap up well before the end of summer, only to resume again toward late winter when plants are fully dormant. Fall garden chores, instead, should focus on weeding, cutting down spent perennials, pulling out dead annuals, planting spring bulbs and mulching beds to protect them for the winter ahead.
When we prune woody plants (aka trees, shrubs and hedges), our cuts may influence the plant to put on new growth. This is especially true when we make shearing cuts. Dormant buds exist all along the length of each branch. Some may be obvious; some may be invisible to the naked eye. However, when we make a cut removing the tips of the branch, we remove a growth hormone that is responsible for keeping those dormant buds inactive. Once that controlling tip bud and hormone are gone, the plant may begin to put on a new growth rapidly. And, when we are cutting out lots of controlling tip buds – as happens whenever we shape up a hedge by shearing it on the outside – we can stimulate a huge flush of this new growth.
So, why is this a bad thing in fall?
Consider this scenario. A large hedge is sheared in October, when the days are shorter and cooler. The growth-controlling hormone tips are shaved off in the process, and a flush of new growth begins to form. This late season re-growth may be relatively slow, and this new foliage is very tender and vulnerable to cold. As the new, sensitive leaves are forming, temperatures suddenly plummet for an early freeze. The delicate new growth is compromised by the chill and dies back. The entire hedge suffers early in the dormant season and is unlikely to recover until spring – if at all.
And if that scenario isn’t enough reason to finish pruning early, consider this one. A focal, privacy hedge is sheared deeply late in the growing season. The season is so late in fact that the plant cannot resource what it needs to put on any new growth. Your privacy hedge no long provides any privacy. Plus, it has now become an ugly set of bare branches and sticks, which will be your view until the growth surge occurs months later in spring.
So, rather than wait to shape up your hedges until autumn, try to complete your last big trim no later than the end of August or very early September*. This way, the plant will have time to briefly recover, put on a small flush of new growth, and be able to protectively harden that growth off before a winter freeze. Then your hedge, pruned properly and timely, should look neat and tidy for winter.
*If your freeze dates come particularly early, mark your calendar to finish up your last shearing on the earlier end of this deadline.