Ask the Gardener: The flowers you should be deadheading

Ask the Expert Gardening
Daisy-like sunflowers, rudbeckia, and asters (above) can provide food and cover for birds if left standing through fall and winter. Adobe Stock

What to do this week: The garden is winding down, but it is still producing, so be selective with your cleanup. To keep the garden looking fresh, cut back tattered or yellowing perennial foliage and pull out annuals that have finished blooming. Do not compost weed seeds or foliage that may contain disease or pests. You can replace flagging container gardens with potted mums. These usually don’t have enough root systems to be winter hardy, so just leave them in their pots and then toss them when they finish blooming. Clean houseplants and their pots that have spent the summer outdoors. Move them indoors on a warm day when they won’t be too shocked by the change in temperature. Patch sparse lawns with grass seed kept constantly moist until it sprouts. Water evergreens throughout the fall to hydrate them fully before the ground freezes and cuts off water to their roots.

Q. What are the most important flowers to deadhead?

N.C., Bailey Island, Maine

A. Deadheading is the removal of spent flowers, especially on annuals, so they will produce more blooms. It’s the same principle as picking vegetables so they will keep producing. Most perennials do not need deadheading because they won’t rebloom anyway. Some seed heads are attractive. More people who like a natural appearance are waiting until early spring to cut them down. Daisy-like sunflowers, rudbeckia, and asters can provide food and cover for birds if left standing through fall and winter.

The only shrubs I deadhead are roses, but I stop doing even that now and let them mature into rose hips so these bushes can wind down for winter. Among the most important perennials to deadhead are phlox, because the offspring from seeds are usually uglier and more vigorous than the parents and crowd out the carefully bred varieties you bought at nurseries. So when the blooms dwindle, off with their flower heads! This late in the year, however, it is easier to just cut down and remove the entire phlox plant as part of your first stage of garden cleanup. Never compost phlox or leave it standing over the winter, as the foliage may harbor mildew spores.

Q. When you talk about planting bulbs, you say, “I always stick some in the holes I dig for other plants.’’ How does that work when the bulb grows from underneath a perennial?

M.S., Milton

A. I usually put the bulbs around the edges of the bottom of the hole and then set the new plant in the middle. The bulbs find their way around the edge of the root ball and grow in a ring. Sometimes I put larger bulbs, like daffodils, around the bottom of the hole, backfill partway, and then add a second shallower ring of small minor bulbs such as crocus before completely filling the hole. (Since the correct planting depth for most bulbs is three times their width, larger bulbs like to be planted deeper than smaller bulbs.) Most of these plants will bloom at different times, so I don’t bother to coordinate colors. I think of this as assembling a kind of horticultural layer cake. Plant fall mail-order bulbs soon after they arrive. They cannot be saved for planting next spring.

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