Of all the chores that gardeners have to accomplish, pruning consistently remains the most mysterious, and I might add controversial. It is perpetually a source of endless conflict or disagreement between some people and of all the classes that we teach here at the nursery, pruning is always a “standing room only” crowd. What, pray tell, is the source of all this consternation?
Mike McGroarty of Freeplants.com has a very simple rule about pruning: “The only time you need to be concerned about when to prune is when you are concerned about cutting off flower buds. Cutting off the flower buds is not going to hurt the plant, it just means that you won't see any flowers this season if you prune at the wrong time.” He also goes on to say that: “If it needs pruning right now, then by all means prune it and worry about flowers later. The damage from not pruning is far worse than any damage you can do with a pair of pruning shears.”
While I heartily agree with Mike, I would add that you will rarely kill anything by pruning it and for the most part, the act of pruning will stimulate growth (this last part is contingent on both timing and severity). The more severe the pruning is, the more aggressive the response of the plant will be and conversely, if we are just taking a little off the sides and the top then the plant may not respond at all. Therein lies the secret of late summer pruning. It’s what I like to call “light pruning”.
“Light pruning”, as defined by The Whistling Gardener, is when we just remove a little bit of growth, mostly through the process of “thinning cuts”. Maybe it is a branch here or there, or a sucker or water sprout, but always it involves removing an entire branch all the way down to where it is connected to another branch. Never do we leave a “stub” because a stub will re-sprout and send out all sorts of new growth, especially if it is early in the season. This is fine, if that is our objective, but that is never the case in late summer. In late summer, we are mostly looking to do a little shaping and forming.
While “light pruning” can be done most any time of the year, it is especially effective in late summer. In the case of fruit trees that tend to generate an incredible amount of suckers (technically called water sprouts), if we prune them out this time of year they will heal over much sooner than in winter but even more importantly, they will tend not to produce as many sprouts the following spring and that can be a huge labor saver. When you think about the practice of pruning and the fact that usually we only do it once a year (and most often in the winter), it is kind of silly. We certainly don’t let our hair grow for 12 months and then chop it all off, but for some reason we think it is fine to treat our shrubs and trees that way. Plants that are vigorous growers and are hacked back once a year will continue to be vigorous growers. But if we do a light trim in the summer, they will start to slow down and over time become much more manageable. Pruning in late summer can break up this vicious cycle and make gardening much more enjoyable.