Ever since I noticed the newspaper article on Dec. 20, 1981, it has been sitting on my desk. The picture caught my eye; it was of a woman and her two grandchildren, who, until she joined a community fuel cooperative, the story said, had been living in a freezing cold house.
What struck me about the photo were the plants in the background. Lined up behind the family stood a parlor palm, a Chinese evergreen and a pothos; none, considering their size and rampant growth, newly acquired, yet flourishing despite an inhospitable environment. I couldn't help wondering: Had the place really been so cold, or are indoor plants more rugged than I was giving them credit for?
The picture returned to my thoughts the other night when my husband complained that our sun room, where we sit and read after dinner, was too chilly. Our plants don't seem to mind, I countered, directing his attention to the geraniums, miniature rose bush and orchid plant, all blooming extravagantly at our large windows.
With energy conservation and costs on everyone's minds these days, especially in the wintertime, I was curious to learn which plants can survive at lower thermostat settings. For enlightenment, I paid a visit to the conservatory in Druid Hill Park (where a dazzling Christmas display, by the way, will continue until Jan. 6) to consult with Larry Ge Smith, the manager and greenhouse supervisor there.
Most house plants, he began, even tropicals, don't need as much warmth as you might think. Temperatures of 60 to 65 degrees Fahrenheit are more to their liking. In the summer heat, plants give off moisture to stay cool, waiting until nighttime when conditions improve to do their growing.
Under cooler and more uniform temperatures, Mr. Smith says, plants don't grow as rapidly, and instead of elongating, develop sturdier stems. In a cooler environment, too, plants don't dry out as quickly and therefore don't need to be watered as often.
People fail to realize, Mr. Smith noted, that the glass in a sunny window acts as a magnifying glass, raising the heat level within the plant and also, in hitting the container, increasing the soil temperature and making the roots uncomfortable as well. Too much heat puts a plant under stress. Symptoms are dulling of its vibrant color and possibly in wilting.
Mr. Smith advises moving plants back or hanging a sheer drapery in front of the glass to reduce glare in a southern or southwestern exposure where the sun is likely to beat down.
Water plants in a cool room early in the day -- between 9 a.m. and 10 a.m. -- to enable them to dry out to some degree before night falls. Plants standing in damp soil in a cold dark room are at risk of developing fungal diseases that are brought on by these conditions.
In a cool room, it can be difficult to tell whether soil in a pot is moist or just cold and thus is in need of watering. To determine which is the case, Mr. Smith says, lay a brown paper towel on top of the soil (he specifies brown because moisture stains on a white background are less noticeable) and press for a minute or two to see whether moisture is absorbed.
In watering in a cool environment, Mr. Smith says, use lukewarm water. Cold water lowers the temperature of the soil and shocks the plant. Plants grow better in warmer soil, he adds, citing as evidence the growth that they produce outdoors in spring after soil temperatures begin to moderate.
In a cool environment, roots rot more readily, especially when soil remains constantly wet. A sign that rot is occurring is the shedding of foliage. And because in the wintertime, too, high humidity is likely to foster the germination and spread of fungal spores, plants indoors at that time of year should not be misted, nor should they be set on trays layered with pebbles and filled with water. By the same token, plants in a cool room in the wintertime have fewer insect problems.
Plants Mr. Smith recommends for a cool indoor environment include: Norfolk island pine; holly fern; dracaena; lady palm; clivia; calatheas; peperomias; sansevieria; aspidistra; dieffenbachia; cactuses; orchids, and oleander.