Growing conditions for houseplants are less than ideal during the winter months. Short days and long nights, low relative humidities, and cold drafts can be stressful to many houseplants. Good consistent care, however, should keep them healthy and attractive.
Many houseplants prefer a relative humidity of 40 to 50 percent. Unfortunately, the humidity level in many homes during the winter months may be only 10 to 20 percent. Humidifiers are an excellent way to increase the relative humidity in the home. Simple cultural practices can also increase the relative humidity around houseplants. Grouping plants together is an easy way to raise humidity levels. The water evaporating from the potting soil, plus water lost through the plant foliage, will increase the relative humidity in the vicinity of the houseplants. Another method is to place houseplants on trays (saucers) filled with pea gravel or pebbles. Add water to the trays, but keep the bottoms of the pots above the water line. The evaporation of water from the trays increases the relative humidity.
Misting houseplants is not an effective way to raise the relative humidity. The plant foliage dries quickly after misting. Misting would have to be done several times a day to be effective and is simply not practical.
To compensate for the short days and long nights of winter, move houseplants closer to windows. However, make sure the houseplant foliage doesn't actually touch the cold window. Supplemental lighting is another option. Light units containing special grow lights can be purchased from mailorder companies or at garden centers. Gardeners can also build their own lighting structure. A standard fluorescent unit containing one cool white 40 watt tube and one warm white 40 watt tube provides adequate light for houseplants. Plants should be placed within 6 to 12 inches of the lights.
In general, houseplants require less frequent watering during the winter months than in spring and summer. As always when watering houseplants, water thoroughly. Water should drain out the bottoms of the pots. If the water drains into a saucer, discard the excess.
The plant species, composition of the potting soil, and environmental conditions in the home, determine watering frequency. Ferns prefer an evenly moist soil and should be watered relatively frequently. Cacti and succulents, on the other hand, should not be watered until the potting soil is completely dry. The majority of houseplants fall between these two groups. Most houseplants should be watered when the soil surface becomes dry to the touch.
Fertilization is generally not necessary during the winter months as most houseplants are growing very little or resting . Resume fertilization in March or April as growing conditions improve and plants begin to grow more actively.
Temperatures of 55 to 70 degrees Fahrenheit are adequate for most houseplants. During the winter months, keep houseplants away from cold drafts, radiators, and hot air vents.
Winter can be a difficult time for houseplants. However, problems can be minimized by providing them with good consistent care.
This article originally appeared in the November 6, 1998 issue, p. 127.