Ask a Local Master Gardener: Time for a winter mulching

  • Blanketing the ground with a layer of mulch, autumn leaves in the foreground bed, or sowing a winter cover crop, as in the background bed, protects the surface layers from pounding rain and wide swings in temperature. AP PHOTO/Lee Reich

For the Gazette
Published: 11/15/2019 3:00:28 AM
Modified: 11/15/2019 3:00:17 AM

Q: When should winter mulches be applied to perennial borders? Can I use my leaves? —J.H., Florence

A: The short answer is “any time now” and “yes, but.” These last couple weeks we have seen overnight temperatures in hard freeze (25 degrees or lower) numbers. This is enough to start the ground freezing and send perennials on their way to slumber in winter dreamland. Now that wintry precipitation is showing up in the forecast, it is prime time for us northern New England gardeners to help buffer our plants from the coming bite of freezing cold air, wind, and the freeze/thaw cycle. Putting down a 2 inch or so layer of mulch around perennials protects them like a gentle blanket keeping them cozy, but not smothered.

If you want to use nature’s leaves, yes you can, but just make sure you remove them from the garden first and shred them before applying as mulch so they break down easily over winter. Oak leaves should get a couple extra passes with the mower (ideally a mulching mower) to help thoroughly cut up their tough, slow-to-break-down outer waxy coating. Using coarse mulch materials such as pine needles or chopped leaves allows for good air circulation and lessens mulch compaction. And, no, pine needles will not break down enough by spring to cause a significant rise in soil acidity, in case you are wondering. Thought I would try to nip that potential question in the bud!

Waiting for a hard freeze is important. Apply winter mulch too early and the captured warmth from the soil may cause new growth — making plants, especially newly-transplanted ones, susceptible to getting that new growth nipped by chilly air. The hard freeze cools the soil. Applying winter mulch after it hits 25 degrees and below means there is less chance of frost damage. Instead, it offers insulation for the coming months when we will likely have frigid temperatures at some point with no protective snow. The leaf or needle mulch will protect the soil and the plants when the snow is not there to serve that important purpose.

If you are curious what the temperature of your soil is, you can purchase a soil thermometer at your local garden center. For a mixed garden, insert it about 5 to 6 inches into the ground. Using a screwdriver to make a pilot hole in the soil first helps protect the thermometer’s probe. From there, simply follow the instructions on the package for a proper reading.

Good question, J.H. Thanks for asking a (local) Master Gardener.

Have a gardening dilemma? Please send questions, along with your name/initials and community, to the Western Massachusetts Master Gardener Association at One question will be answered per week.

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115 Conz Street
Northampton, MA 01061


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