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Some timely answers to those cutting-back questions

People ask me so many gardening questions, and most of them start with, “When do I cut back my ...?” The plants vary, from houseplants to trees, but cutting back is on our collective minds. Here are some of your questions – and my answers:

Our hydrangeas are out of control – tall, tall, tall and drooping over the driveway. This would play havoc with the snowblower. Will pruning them cause injury or spring-growth problems? How much can we cut them off?”

If you have the reblooming type of hydrangeas such as ‘Endless Summer’ and kin, typical advice would be to enjoy their looks now and leave those stems standing through winter. New flowers will develop on them by June.

If you cut them off now – let’s say 4 inches above the crown or soil level – you won’t damage the plant itself, but you may not see flowers until later. If you are talking about taller kinds of hydrangeas, such as ‘Annabelle’ or the many other “panicle” cultivars, they usually don’t require pruning. Still, if you do cut them all the way down, they will usually regrow.

But let’s face it: The placement of those hydrangeas isn’t so great. In itself, snow doesn’t harm plants (woody or otherwise) and is an excellent mulch. But snow pounded onto plants by a snowblower or – worse – pushed onto them by a plow can certainly damage, break or uproot them. Perhaps move them farther from the driveway – an island in the lawn? – or stake off the snowblowing area so the landscape bed is less affected. After the ground has frozen, cover the hydrangea crowns with 6 or 8 inches of mulch. Doing that might increase bud development and protect the plant somewhat.

I grew last year’s amaryllis on the deck and brought them in with the houseplants, and now what? Is this the time to cut back the leaves?

It’s good you got the amaryllis in before a freeze. You don’t have to cut back leaves until they dry up (although growers do so for efficiency), but you do have to simulate a tropical winter to force dormancy. Put the potted bulbs into a cool place (basement or attached garage?) at about 50 to 55 degrees and cut back any leaves as they turn brown.

After six weeks or more, move them into warmth and light, and fertilize and water lightly as growth begins. (Overwatering is the killer.) You can repot at this time – only an inch larger pot size – but they benefit from being crowded. Amaryllis tend to bloom roughly seven weeks after they start to grow.

When do I cut back the butterfly bush?

If you wait until midspring, you might increase the plant’s survival odds slightly since the crown offers some winter protection. Also you might find living tissue partway up the stem in spring, so you could have a larger butterfly bush if you like. Same goes for Carytoperis.

My red mandevilla finally was loaded with flowers, and I just had to bring it inside! People told me to cut it back, but do I have to?

Oh why would you cut back a flowering plant? Just enjoy it! This applies to many flowering container plants. Sometime around December the flowers will quit, so cut it back (a judgment call, but I cut to about 8 inches, stop the fertilizer and lighten up on watering). Some people put these plants in the cool basement, and others keep them as houseplants. In late winter provide the best light possible and start fertilizing. Repot when the roots are crammed.

We put in this new landscape a few years ago, and the bushes are getting too big. Can I trim them now?

When to prune the landscape plants is not a simple answer since it depends on what plants you have. Mostly it is not the best time of year to prune most shrubs anyway. (In horticulture language, “shrubs” is the right term for multistemmed plants rather than “bushes.”) Do cut off branches that are diseased or broken or that interfere with your sight lines or a walkway, but don’t do an overall job now.

Another usage tip: Let’s use the word “prune” instead of “trim.” The image of “trimming” suggests the wrong way to handle most pruning jobs, implying haircut-style clipping or cutting off all the tips to make a plant evenly flat-topped or rounded. Save that for hedges or topiaries and make selective pruning cuts at varying levels for most shrubs or trees – mostly not now. Pruning is a fairly complicated art and science, and I’ll offer lots more guidance in late winter – the best time to prune most woody plants.

I have a huge silver maple tree, and it survived the October Surprise storm in 2006. But it’s been dropping a lot, and one big branch is hanging over our roof just above the bedroom. You said not to prune in the fall, but I’m worried.

Uh-oh. Yes, I’ve often explained that late summer and early fall are the worst times to prune most woody plants, in general. That is because pruning opens wounds that are vulnerable to rot diseases, and wounds seal over best in spring. Also, pruning at the end of the growing season can stimulate new growth just when the plant is supposed to go dormant. BUT if a limb is endangering life or property, or if a tree canopy is crowded and dropping lots of branches, this is the time to take action. If the problems are up in a tree, do not try to solve things yourself. Call a professional arborist. If the pro says to prune, do that.

Also, know that many trees that apparently “recovered” since 2006 did not necessarily get correct pruning to produce a strong branching structure, so they filled out with weak growth and dense shoots – not necessarily healthy or sustainable. That tree may need repeated visits for long-term health.

Let’s get past all this cutting back and move on to the joy of growing our plants!

Sally Cunningham is a garden writer, lecturer and consultant.

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