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Ask the Gardener: Does it really matter if you deadhead flowers?

Award-winning garden writer Carol Stocker talks about plant care, seedlings, and propagating irises.

The popular “bearded’’ iris gets it name from three fuzzy strips radiating from the center of the colorful flower. Globe file/2003

What to do this week: Cutting or pinching off spent flowers encourages vigor, neatness, and often rebloom on most annuals and some perennials. Mow natural meadows once now and once again in late fall to discourage a takeover by invasive weeds, vines, and woodies. Don’t let lawn crews scalp grass in hot weather, when the growth rate slows, just to keep themselves busy. Let grass grow high to shade roots and retain moisture. Clip and discard all spent peony flowers and blackened stalks or foliage to discourage botrytis blight. Wipe pruners with alcohol-soaked cotton as you prune disease-prone plants. Lightly fertilize annuals, roses, and vegetables once a month just before you water or when rain is due. Most trees, shrubs, and perennials do not require fertilizing, and lawns need it only once a year, in the fall. Harvest garlic when the top five leaves start to brown.

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Q. Does it really matter if I deadhead flowers? Aren’t there some that do better if I let them go to seed?

N.M., Milton

A. Snapping off spent flowers usually doesn’t affect woody plants, but most perennials and annuals will decline if allowed to go to seed. The exception to this rule is biennials, which live only two years and are probably going to die after blooming whether you deadhead them or not. They have a surprising two-year life cycle. Most sprout from seed one year, quickly flower the following May, go to seed in June, and turn brown and die by July, exhausted by creating hundreds of new seedlings. Some of the worst pests, such as garlic mustard, wild chervil, and thistles, are all biennials that must be pulled or mowed each May before they go to seed. But other biennials are charming garden flowers, including species of hollyhock, foxglove, Canterbury bells, gilliflower, California poppy, pansy, forget-me-not, sweet William, columbine, wallflower, and feverfew. Letting them go to seed produces a random scattering of blooms denoting an ever-changing, old-fashioned “cottage garden’’ rather than a more planned and perhaps stiffer-looking modern garden.

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Q. My iris doesn’t bloom much anymore. Does this mean I have to move it?

A.K., Watertown

A. Moving it to a sunnier spot may solve your problem, but divide it while you’re at it so it has room to spread out. You probably have the popular “bearded’’ iris, which gets it name from three fuzzy strips radiating from the center of the colorful flower. Pry out the fleshy rhizomes (roots), which look a bit like culinary ginger and grow just under the surface. You can cut them into 6-inch pieces with a clean knife and discard any roots that are soft or diseased. Replant these smaller rhizomes horizontally just beneath the soil surface, root side down and 3 feet apart in a sunny spot. There are also many kinds of so-called “beardless’’ iris that lack the fuzzy flower strips. These include moisture-loving Louisiana and Japanese iris and the easier and more popular Siberian iris. These seldom need division to keep blooming, but if you want to propagate them, just use a sharp spade to slice off and dig up a piece of root without lifting the entire plant.

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