Thirst Aid for Houseplants
It looks like cold weather is here to stay, so keep in mind that the
typical household in winter is a hazardous place for houseplants. Although
we grow them indoors, most houseplants are outdoor plants in their native
climates. Tropical and subtropical species can be damaged by temperatures
below 50 F, but being too warm in winter can also be a problem.
The air in most homes becomes extremely dry as furnaces force warm air
through the rooms. It is not unusual for relative humidity (RH) inside
the home to drop to 15 percent during the winter heating season. Most
houseplants do best at about 35-45 percent RH.
Warm temperatures, coupled with low humidity, can cause plants to lose
water faster than they can take it up. So, even though the soil may hold
plenty of moisture, the leaves may begin to droop and/or turn brown along
the edges. Hot, dry, stale air also creates a favorable environment for
spider mites to become troublesome.
The most effective way to increase RH for the comfort of both plants
and people is to run a humidifier. Grouping plants together on pebble
trays filled with water can also help. However, misting plants occasionally
with a spray bottle adds such temporary moisture that it does not effectively
change the relative humidity. Keep all plants away from hot air drafts
near heat registers. Ferns are especially sensitive to dry air, so take
care to place them in a protected area.
Although some plants may grow more slowly during the short days of winter,
dry air can cause them to need to be watered even more frequently than
when they were actively growing. Monitor the soil moisture to be sure
that plants are getting watered as needed.