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January 10, 2006
Prepare Your Houseplants for Winter
Days are getting shorter, nights are getting colder, and winter is fast approaching. It’s time to focus our attention on our indoor plants. Should we be concerned with houseplants in winter? After all, aren’t they growing in a controlled environment, shielded from the elements? The fact is that seasonal change outdoors does affect our indoor plants. Also, our controlled indoor environment can itself introduce additional stress to our plants. These changes in light, temperature, humidity, as well as our ingrained watering habits can all contribute to stress houseplants. In the aggregate, these stresses can produce weak or leggy growth, and pallid or browning foliage. If we understand the origin and nature of these stresses we can act to reduce them.
Fall and winter months bring the time of year when sunlight is neither as abundant nor as intense as during the outdoor growing season. Unless you grow your plants 12 inches under fluorescent lights, the usual locations of your houseplants may no longer meet their basic light levels. All know that the duration of sunlight varies throughout the year and is at a minimum in mid-winter. Passing storms can bring repeated days with cloudy skies. Even when the sun does shine, it is lower in the sky so that its rays strike the earth (and our houseplants) at a more oblique angle. This results in sunlight of a weakened intensity. Houseplants that have summered outdoors, even in a shaded location, are very vulnerable to this stress of reduced sunlight indoors.
A second and lesser factor that affects the sunlight available to indoor plants pertains to the fact that sunlight has to travel through our windows. While clean glass has excellent transparency qualities, who among us ventures outdoors to wash windows in January?! Plastic or lucite glazing is even less forgiving than glass. So while the foliage may be gone from that shade tree in front of the window, snow and rain will nonetheless leave a film on the window surface. Although minor, these deposits will further dilute the effective sunlight that can pass through a window. Screens, blinds, and curtains will reduce even more the amount of sunlight that is available for our plants. So if that African violet in your east window seems to languish pallidly during the winter months, it may be because it isn’t receiving enough sunlight – you may try moving it to a more southerly exposure and/or giving it less water.
Why should we be concerned with temperature when our homes are heated at this time of year? First, even if we set our thermostats back at night or allow the stove to burn down, the indoor daily range between the extremes of high and low temperatures is usually much less than that which most plants normally would experience in their natural habitat. There is not much that we can do with our living quarters to compensate for this abnormality. A second consequence of heating our homes is that the indoor environment can become very dry. This lowered humidity may cause our plants to develop brown edges or leaf tips, particularly those that are native to tropical climates. A saucer filled with pebbles and water will help if the water level is maintained at just below the bottom of the pot. The pebbles promote evaporation of the water. An added strategy to combat dry air is to group our houseplants so that they benefit from their collective transpiration.
Another temperature-related consequence comes from the existence of indoor microclimates. Although a thermostat on an interior wall may read 67, the temperature along an exterior wall or by a less than tight window or door may be several degrees cooler. Placement of our houseplants should be guided and, if need be, adjusted by knowing of the existence of these microclimates. For example, they should never be placed where there will be sudden, dramatic fluctuations in temperature, as by an exterior door.
There remains one final factor to consider. Reduced and less intense sunlight, a shrunken daily temperature range, and less than optimum humidity all conspire to strain our plants during winter. If we continue to maintain our customary watering schedule through the winter, we are unwittingly adding to the stress on our plants and are likely encouraging leggy and weak growth. Simply stated, with less solar energy available, less photosynthesis is possible. Therefore, we should be watering less, either in frequency or amount. This tried and true rule applies year-round: water a plant only when its soil surface has become dry and then water it thoroughly. Moreover and unless you are growing under artificial lights, it almost goes without saying that feeding indoor plants at this time of year - say December through February - is totally unnecessary and may be counterproductive by stimulating growth that is bound to be weak, leggy, and limp. A final tip to avoid lopsided growth: Rotate your plants ¼ turn each time you water.
By tony Croce
The author is a Master Gardener volunteer for the University of Arizona Coconino County Cooperative Extension.
Posted by maxmaddy at January 10, 2006 1:03 PM