If you've given houseplants a vacation in the sun, it's time for them to come back into the house. Before bringing them in, do a bit of grooming.
Many can benefit from a shower to wash away webs,critters and grime. One can use a bit of mild dish detergent (2 teaspoons per gallon of water) to wash each leaf by hand. I like to remove foliage that is past its prime as well. If needed, this is the perfect time to repot them. At least wipe off each container and carefully check saucers for cracks. Indoors, I like to use rather deep ones to reduce the chance of flooding the carpet or floor.
If you find a sticky pot or leaf, the plant may have scale, an extremely common problem which is very difficult to eradicate. There are about 1000 species of these small (1/16-1/4-inch) insects in North America. They are found on trees and shrubs, in greenhouses and on houseplants. Whether "soft" or "hard", the adults live under a protective coating in one spot sucking sap from the plant, excreting "honeydew" and reproducing. The "crawlers" move away from mom to find a spot on a stem or a leaf and begin a lifetime of sucking sap, et cetera. Females reproduce asexually. (If you care for the details, ask an entomologist.) The males have wings, do not feed on plants and are seldom seen.
If the infestation is in a limited area, prune out that part of the plant, bag it and place in the trash. One can try to remove the insects, but the coating makes this very difficult. I fought this problem on a nice little laurel tree and lost. It probably had scale when purchased. It is a good idea to keep a new plant in quarantine until one is certain it is OK.
Back in the house, the plants may need some time to adjust to the lower light level. Plants naturally slow their growth during the shorter days of late autumn and winter, thus having reduced needs for water and fertilizer.
Houseplants are meant to be decorative. When one is failing the ornamental test, it is time to find a replacement. We'll explore some seasonal options in a future edition.