The record-cold weather in the East this winter has had a devastating effect on many tender indoor plants, despite a room temperature of 66 or 68 degrees. Why? Window temperature is the answer.
A window acts like a wall of ice. A plant sitting near it is giving off more heat than it receives from the room. Remember, heat travels from places of higher temperature to places of lower temperature. Also, a cold window creates a draft.
Air, cooled by the window, tends to become heavier and settle, thus making a chilling draft for tender plants.
If you live in an average home, you're losing from 25 to 35 percent of the heat through the windows, even though they may account for no more than 15 percent of the wall surface.
Even in a well-insulated house, heat loss through the windows may be as high as 50 or 60 percent of the home's total heat loss.
Of course, windows aren't all bad. For about 8 hours a day during the winter months they can let in the sun to heat the house free of charge. And that's the secret: Let the sun in during the day but keep the heat in and the cold out at night.
Here's what to do:
* Since your plants are losing heat to the glass, draw the shades at night and close the draperies and venetian blinds.
* On really cold nights use newspapers to cover any plants that are near the windows.
* If you have cold weather plus wind, move any tender plants to the center of the room. Such plants as African violets and most foliage plants will not tolerate temperatures much below 50 degrees F. and will wilt beyond the point of no return.
Pay attention to the weatherman when he gives the wind-chill factor, which takes into consideration the speed of the wind. You may find it is colder than you think, thus affecting your heat loss indoors. For example, if the thermometer reads a plus-20 degrees F. and the wind velocity is 15 miles an hour , the wind-chill factor is a minus 5 degrees F.
Or let's say the outdoor thermometer reads zero and the wind velocity is 10 miles an hour, the wind-chill reading is minus 21 degrees.
Remember, too, the greater the wind velocity, the more cold air is going to be forced into your home.
Indoor plants come up against another problem associated with cold weather. Tap water can be close to 35 degrees F. or colder in the wintertime. If applied directly out of the tap, it can lower the soil temperature considerably, making it impossible for plant roots to take up water.
It is especially detrimental to germinating seeds. Most seeds do not germinate well unless the temperature is 68 to 70 degrees day and night.
Tests have shown that when 40- to 50-degree water is applied to germinating seedbeds, the temperature of the beds is lowered to almost the temperature of the water applied. It takes 4 to 6 hours to get it back up to a maximum temperature of 68 degrees, even though the room temperature is kept at 68 degrees constantly.
The solution is to draw off the water at night and let it stand at room temperature overnight.
If you set the thermostat lower at night, you may want to let the water sit longer in the morning before watering, or else add a little warm water to it. If you're trying to germinate seeds, you can ensure a constant 68 to 70 degrees by using a small, inexpensive heating cable under the box and by keeping the seed box covered with polyethylene sheet (a bread wrapper or cleaner bag will do fine).
You can subirrigate by setting the box in a pan, or you can use a poultry baster to water the plants.
Another good reason for letting the water sit overnight is that chlorine and fluorine will dissipate. These elements can cause browning of the tips of leaves on such plants as chlorophytum (spider plant) and members of the draca ena family.