Winter Houseplants

The instructions on the jar of houseplant fertilizer sitting in front of me are so clear—and so wrong. "Mix 1/4 teaspoon of fertilizer per quart of water and water plants normally. Feed every two or three weeks." But plants aren't machines, fueled on a set schedule! They're living things, and just now, they're not hungry.

Outside, it's cold and dark. Even though it's warm and lamp-lit indoors, houseplants still feel, and are influenced, by the changing of seasons. It's winter and plants are growing slowly, if at all. We have to adjust our care of houseplants accordingly, slackening off on the amounts of fertilizer and water we offer.

A little extra fertilizer won't hurt, you say. At best, extra fertilizer is merely wasted as it washes out the drainage hole in the bottom of a flowerpot. At worst, though, that extra fertilizer builds up in the soil as salts, which then dry out roots. A white crust on the soil surface and browning of leaf margins are signs of this problem. The cure is to water heavily a few times to wash the salts down and out of the soil.

I don't fertilize houseplants at all this time of year because the soil and compost in my potting mix release nutrients naturally. Most commercial potting mixes lack real soil or compost and contain only a little fertilizer to get plants started. For plants growing in such "soilless mixes," a general rule is to fertilize at half strength this time of year. But don't fertilize blindly. Look at your plants and if the old leaves are yellowing and dropping off, feed a little more. In a couple of months, lengthening days will make plants more hungry.

The situation is similar with watering—plants need least this time of year. Outside, last summer, my poinsettia required almost daily watering, growing rapidly as it bathed in sunlight and warm, drying winds. Now this same plant is growing slowly, if at all, in its winter home in the cooler, still air and reduced light of my living room. Once a week watering is adequate.

The surest way to tell whether a plant needs water is to poke your finger into the soil. But who wants dirty fingernails every day? Now I just lift small pots, and their weight tells me how much water they need. Some people listen as they knock on their pots to tell how wet the soil is. You can also tell whether watering is needed by poking an inexpensive electronic moisture meter into the soil. Most plants like their soil constantly moist; let the soil for succulents go bone dry between waterings.

Hardy bulbs are the exception to the rule that plants should not be coaxed along this time of year. Daffodils, crocuses, and hyacinths that I potted up for indoor blossoms a couple of months ago are ready to spring into action. Their growth should be held back ever so slightly, with cool temperatures, so that their petals unfurl into shapely blossoms. Aside from that, I water them commensurately with their increasingly rapid growth. Focus your attention on forcing the growth of potted bulbs and let the rest of the houseplants plod along for now.

Lee Reich