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How To Protect Your Garden From End-of-Season Pests, According to a Plant Doctor

Allie Flinn

October 16, 2021

The end of harvest season is nigh, but before you pack up your tools, it's important to take measures to protect your plants from overwinter garden pests, like certain beetles, worms, and borers. While you may not notice these critters when it’s cold out because they burrow into the soil to wait out the freeze and lay their eggs, you will when they emerge come spring to wreak havoc on your garden. "If you had these pests during the summer, then you can bet they’re looking for a place to overwinter in your garden," says Rebecca Sears, chief gardener at Ferry-Morse.

"The very best thing you can do is to commit to a post-season clean-up," says Sears. "As soon as you’ve finished harvesting, pull up and remove the old plants plus any weeds so that the bugs don’t have a place to hide and keep warm. This will also expose the soil to birds who are happy to help you keep pests in check by eating eggs and larvae." She explains that this is important to keep your garden healthy, as these pests can stress out—and even kill—your plants, as well as spread disease.

Experts In This Article

Chris Satch, horticulture consultant and professor of plant biology and pathology at the New York Botanical Garden
Rebecca Sears, chief gardener at Ferry-Morse Seed Company

Overwinter pests can also strike indoors. "Many folks put their plants outdoors in the summer to cash in on the abundance of sunlight and capitalize on plant growth; however, plants tend to pick up a few pests when they’re outside. The most common pests outdoors that hitch a ride indoors, come fall/winter, are aphids and thrips," says Chris Satch, a plant doctor for Horti. But the arch enemy of the season for indoor plants is the spider mite. Your plants can pick up spider mites from being outdoors, or even from being near an open window. They thrive in hot, dry environments—like inside a house that's got the heat cranked up.

Caught early, you may be able to spot and eliminate these pests before they cause much damage, says Satch. "Basically, if anything seems amiss with a leaf, it probably is," he adds. "Mite damage looks like someone took a needle and poked grey/white, sometimes translucent dots on the plant. Thrips make CD-scratch patterns, black dots, and other messes all over the leaves." (He notes, however, that browning or blackening splotches on the leaves are caused by bacteria or fungi, not pests.)

All in all, tending to the health of your plants is a lot like ensuring the health of yourself—a proactive approach leads to best results. "In the fall, it's all about preventing pests from establishing a foothold so that they don't plague you through the winter," Satch says. He recommends that you quarantine any plants you bring inside—whether they're from the plant store or your outdoor garden. "Treat with a pesticide of your choice at least two to three times over the period of a few days," he says. "Personally I spray insecticide on my plants the minute they come in the door, the next day, then two days after that to make a total of three applications over about four days. Once the final application is dry, I wash them in the shower, then add them to the windowsill where they can soak up the rays of the direct sun." Also, it's a good idea to spray the rest of your plants to be super safe, he says.

And should your plant bbys succumb to overwinter pests, Sears offers one final word of advice: "If you know you had pest or fungus problems, do not compost your expired plants as you’ll be introducing those problems back into your garden the following year."

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