Houseplant hospital

How to keep your plants alive over the winter

By Soncirey Mitchell
Reader Staff

Winter is peak mortality season for desk cactuses and bathroom ferns, which suddenly seem to brown and wilt when the weather gets cold. They may be toasty indoors, but houseplants still enter into a dormant period in the winter; and, when combined with a heated home, that means the usual care methods just don’t cut it. Below are a few tricks to combat common cold-weather issues.

Most people water their houseplants once a week without thinking about it, which works for most of the year. With the decrease in sunlight in winter, though, most plants go dormant and stop producing new growth, even if the old growth stays green. Because they aren’t expending energy creating new leaves, plants don’t need the same levels of water or fertilizer, and feeding them the usual amount as in the summer will damage the roots.

Constantly moist soil encourages fungal growth, root rot and pests that feed on decaying plant matter. Keep the plant food on the shelf, and always poke around in the soil with your finger to make sure it’s completely dry before watering.

Though they’re taking in less water through their roots, most houseplants originate in tropical climates and rely on humidity to keep their foliage healthy and hydrated. This makes winter an especially hostile climate for them, even though they’re toasty inside, because the heaters and stoves suck the moisture from the air. 

The easiest way to counteract this — and help your sinuses — is to run a humidifier throughout the cold months. If that sounds too expensive, thoroughly rinse an old spray bottle of cleaning supplies (or buy a new one) and mist the plants by hand every other day.

Be sure to locate vents and air patterns in the home to ensure plants aren’t directly exposed to warm air, as this will quickly crisp the leaves, no matter the humidity.

Winter is also the time when indoor pests that have been dormant in the soil or in the folds of the plant come out to wreak havoc. You might begin to see thick spiderwebs appearing around the leaves of a plant, accompanied by small white, brown and/or red specks. These are spider mites, and they’re sucking the moisture out of your leaves.

To treat spider mites, first quarantine the plant and any others touching it, and remove damaged leaves. Take the plant into the shower or kitchen sink and spray down the pot, stems and leaves, wiping away the fine webs. Next, create a mixture of one part alcohol, four parts water and a few drops of dish soap, and use it to thoroughly coat the plant. 

This can damage some species’ leaves; so, before applying, Google the species or begin with a tester leaf and wait a few days to see if it survives. With the plant coated, use an old paintbrush or toothbrush to push the concoction into the plant’s crevices, sweeping up any leftover eggs or webs and paying special attention to the undersides of leaves. Finally, set the plant in front of a fan to dry, and repeat the process every four days for two weeks or until the problem is gone. After all is said and done, rinse the plant off with plain water.

While spider mites are likely, fungus gnats are inevitable — and worse, they can fly, making quarantining them a difficult prospect. The insects look similar to minuscule mosquitoes, flying up and around plants and landing in people’s drinks while their larvae feed on plant roots. Allowing plants’ soil to dry out before watering helps starve them out; but, once the adults appear, the only way to kill them is through yellow sticky traps (available at most home and garden stores) or cups of apple cider vinegar mixed with dish soap, both of which lure them to their deaths.

To kill the offending larvae and eggs hidden in the soil, drench the dirt evenly with a mixture of one part 3% hydrogen peroxide and four parts water every three to seven days for two weeks, or until you stop accidentally inhaling bugs.

Shepherding plants through the dark months can be a bit of a challenge, but having cleaner air and a pop of color when the world is gray is worth it in the long run.