Ask the Gardener: Should you skip moving plants in this drought?

Plus, how to care for peonies with powdery mildew.

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A powdery mildew on peonies is common when summer has high humidity.

What to do this week Buy a rain gauge and continue watering gardens any week we get less than an inch of rain. (Be sure to follow local watering restrictions). If you have a struggling tree that needs extra moisture, such as an American dogwood, dig a hole 9 inches deep (where the tree roots are), and if the bottom is dry, water the ground under the tree canopy. Weed and spread organic soil amendments such as compost before mulching the garden. Wait until spring to prune woody plants, because dead-looking branches may eventually resprout. But go ahead and pull out spent annuals and vegetables, and cut down perennials whose foliage looks bad, like yellow day lily leaves and peonies or phlox with powdery mildew. They’ll be back next year. Cut back discoloring stems of flowering geraniums, petunias, and other blooming annuals to healthy new leaf growth to encourage reblooming, but leave rose hips unpruned to help rose bushes prepare for the winter. Pinch off the tips of Brussels sprouts plants and tomato stems to hasten the ripening of existing fruit. Sow fast-growing cool-weather vegetables such as radish, arugula, and mâche.


Q. Ordinarily, every fall I make lots of garden moves, dividing irises and other plants on a rotating schedule, moving plants that aren’t thriving in one spot to another, etc. I’m wondering whether due to the drought conditions this summer, I ought to leave everything as is. Are the plants too stressed to be moved? Would your recommendation change if we had a very rainy September?

B.P., Southborough

A. This summer’s heat and drought have indeed been an ordeal for plants, especially woodies, that argues against stressing them further. But there is plenty you can do if you are itching to work in the garden. My major activity this fall will be to re-mulch my landscape with 2 or 3 inches of new shredded bark or wood chips to help protect it from future extreme weather. Mulching minimizes moisture loss and maintains more even soil temperatures, while helping prevent soil from being washed away if we get the torrential rains that can also result from climate change. Mulching also reduces weed germination and protects trees and their roots from mowing equipment and weed whackers.

I am going to reduce my gas-guzzling lawn further by removing grass growing under tree canopies that compete with tree roots for moisture (and usually wins). During future heat waves, I’d rather keep my trees than my lawn. I will start mulching a foot from the base of the tree trunks and shrub stems, because piling a “mulch volcano” right up against a trunk can rot it. I want a doughnut-hole effect. My gardens have been mulched many times over the years, so what I am really doing is replenishing previous mulch, which has broken down into new soil. I do not mulch with rocks, weed-block fabric, or artificial turf over tree-root zones (the area under the canopy) because they trap heat in the soil and increase water runoff.


Q. All the leaves on my peonies have a gray substance on them that must be mold. Is that dangerous to the plant or other plants? No other plant seems to have it so far.

J.C., Dover, N.H.

A. Your peonies have powdery mildew, which is common when summer has high humidity. It is ugly and almost impossible to get rid of once the soil is infected, but seldom fatal. I just try to keep it under control by thinning crowded plants in the spring that are particularly susceptible, such as phlox, bee balm, and asters and removing badly mildewed individual stems. I never compost these kinds of plants, and shop for varieties labeled “mildew resistant.” I have read that as a preventative in May or June you can spray leaves with Neem or with a solution of one part milk to nine parts water, though I’ve never tried this. I just regard powdery mildew as one of many unsightly nuisances that frustrate the gardener’s quest for visual perfection.

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