Q. Mike: You have given us guidelines about when not to prune ("the Fall"), but I could use a rule of thumb for when it is officially 'that time' in the Philadelphia suburbs where I live. After which date or natural phenomenon should one no longer prune live wood until obvious winter?
- ---Carol in Wynnewood, PA
A. Great question, Carol. And I have to admit that the answer is a little slippery. If such a 'drop dead' date did exist, it would have to be tempered greatly by your USDA growing zone and the reality of the then-current and upcoming weather. Maybe the best way to approach this topic is to break it down into the three kinds of plants we gardeners most feel the need to prune.
The first category is Spring bloomers like azaleas, rhododendrons, lilacs, forsythia, dogwoods and 'fruit trees', both edible and ornamental. Gardeners really should do all this pruning within a month of the flowers having faded in the Spring—for several reasons. One, it removes any unwanted seed heads that would otherwise sap energy from the plant if left in place. Second, it is the safest time of year to dramatically reshape plants and cut overgrown specimens back, as the plants are at their most vigorous and can recover fast. And you won't risk removing any developing flower buds and thus lessen the following year's show.
Can you safely prune Spring bloomers a month later? Almost certainly. A month after that, however, summer may be slapping them around with a torrid hand, any seed heads would have already finished sucking all that vigor from the plant, and you're now in the window where you are beginning to risk accidental flower bud removal. Mid-summer, heat stress is reason enough to play hide the pruners. And from then on, you know the buds are all fully formed, and pruning will turn your Spring show into a no-show.
Summer bloomers? Well, they're still blooming in the summer! The only pruning you should do then is to cut flowers for indoor display—and do this you should, especially with roses, most varieties of which will respond to such a cut with another run of blooms. Ah, but as the days get shorter and you experience the first August night that tempts you to turn on the heat ("c'mon, honey—just a little bit"), the pruners should go away. Your plants are beginning to settle in to their first stages of dormancy, and cutting now will sap some of the vigor they need to get through a harsh winter.
You want a date? A time? A sign? August pruning should be for cut flowers for indoor display only. And as soon as you see the first school buses taking their young prisoners back and forth to the penitentiary, the pruners should be sharpened, oiled and stored safely away.
The third group is deciduous trees, which are best pruned when you don't want to; in the dead of winter. Most can also be pruned in the Spring—just look up your specific tree first to make sure it isn't a Chuck Wepner 'bleeder' that sends sap sailing when pruned in the Spring (like maples); always prune those types mid-winter.
I understand the impulse/temptation/itch to prune in September. The weather is nice, the tomatoes are shot, summer's over, we're bored, and all we have to look forward to is replacing boredom with depression---of course we want to go out and prune! Same with November, which may be the worst month to cut. The plants are three-quarters dormant by then, and stimulating new growth by pruning is sure to both sap their strength and cause weak new growth that will be very prone to winter injury—especially if that warm day that lured you into pruning is followed by a few more warm ones and then a hard freeze. Ouch goes the lush new growth.
December, however, brings both challenge and opportunity. The plants are deeper into their REM-like sleep, and the holidays during which many of us infest our homes with greenery are fast approaching. So while Spring bloomers and deciduous trees should still be left alone, overgrown evergreens deserve a close look.
For instance, I have a big old blue spruce that, if left untouched, will work its way into the power lines in a few years. This summer, I convinced the electric company's tree whackers to leave it alone so that I can carefully fell it (away from the power lines) mid-December. I'll use all of the lower branches to make wreaths, swags and garlands and then prune the top topiary style to make this year's Christmas tree. Doesn't matter how ratty the bottoms of these trees get, the tops are always perfect.
Of course, this is culling, not pruning. In a typical year, I'll instead harvest whole evergreen branches that are either beginning to brown out or that are getting in my way. I'll wait as long into December as I can, I'll put it off if any freak warm spells are predicted, and I'll harvest only entire branches to limit the possibility of regrowth.
Same with hollies and other winter berry-bearers. Come mid-December, I'll take the same chance and harvest entire branches during a cold spell, and use the cuttings to top off my evergreen arrangements. Yes, I should wait another month, but most seasons, the weather is cold enough to do this safely.
And besides—what am I supposed to do with holly branches in January?!