Q: Do pine needles make good winter mulch, or will they change the acidity of the soil? A: Pine needles make an excellent organic winter...

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Q: Do pine needles make good winter mulch, or will they change the acidity of the soil?

A: Pine needles make an excellent organic winter mulch. Thanks to their curved shape, they “breathe” well, so they don’t trap excessive moisture, which can lead to mold and disease. They are also easy to clean out of the garden when spring arrives — an important quality, since too much mulch can smother new growth.

During winter months, the primary goal of mulching is to protect young plants from heaving — the repeated freezing and thawing of the soil — a process that can leave delicate roots exposed. The mulch’s insulating barrier keeps the ground at a steady, cold temperature throughout the season.

To mulch correctly, wait until after the first frost, then apply a layer about 2 inches thick around young plants. Don’t mulch too early, or too heavily, as this can encourage small rodents to nest in your garden.

You may be able to gather plenty of pine needles from beneath the trees on your property; if not, most garden centers sell pine needle mulch. You can even use the boughs of your Christmas tree for the same purpose: Once the holiday has passed, take the old tree outside, and cut off its branches, laying them over garden beds in a crisscrossing fashion.

Pine needles are slow to decompose, and they won’t significantly change the acidity in your soil when using pine mulch, especially if you remove it in the spring.

Questions may be sent to mslletters@marthastewart.com or Ask Martha, care of Letters Department, Martha Stewart Living, 11 W. 42nd St., New York, N.Y. 10036. Sorry, no personal replies.