Q: I’m afraid I overpruned my climbing roses this spring. Twelve weeks later, the rose plants still look terrible. Is there any hope that they will bloom again? — Diana Rodriguez, Bronx, N.Y.
A: Sorry, but your climbers won’t flower much, if at all, this season. That, however, is your only loss. By next spring the roses will be back in fine form and blooming. You can’t seriously damage a rose by cutting it back. In fact, a severe pruning is a time-tested way to rejuvenate a plant that has stopped sending up vigorous shoots. You could run amok with a lawn mower over hybrid teas and floribundas, and they’d grow back and bloom the same summer. But climbers — with the long canes that make them ideal for training onto trellises and arbors — need more time to recover from radical pruning.
The best time to perform major pruning (removing one or more canes) on a climber is right after it has finished flowering, in early summer. The strong new canes that sprout afterward will then have time to mature and produce roses the next year. Early-spring pruning of climbers should be very light, removing only winter-killed wood on canes and branches. On varieties that rebloom during the summer, you can also shorten sideshoots in the spring to stimulate new growth that produces the best flowers. After the first bloom, deadhead the sideshoots to promote the next wave of flowers. Without periodic removal of its oldest canes, a climber will become an overgrown thicket. When you are pruning in the summer, cut out the whole length of a thick, woody old cane — no simple matter, because each cane’s innumerable branches get tangled with those of neighboring canes. Resist the temptation to start at the top, where it’s easiest to cut with ordinary pruning shears: It’s also easy to clip off what you think is a branch of the old cane, only to realize that you’ve severed the intertwined stem of a desirable young cane. Instead, wielding heavy lopping shears, begin at the base of an old cane and remove only as much of it as you can easily extract. Then lay down the shears and wait. Within an hour, the leaves above where you’ve cut will begin to wilt, making it easier to tell which of the tangled branches belong to that cane. Clip out branches with wilted foliage until every bit of the cane is gone.
Most climbers can then flourish for several years before needing another major pruning to stimulate new growth. Exactly when depends on the vigor of each variety and how you have it trained. For example, if a rose fanned out against a wooden lattice has five major canes, you might renew it on a five-year cycle by removing only the oldest, thickest cane each summer, after flowering. If the rose overgrows the trellis on that schedule, take out two canes each summer. A rose climbing a large arbor or scrambling through a tree will need less pruning; taking out the oldest cane every other summer should be enough.