Put ‘bring houseplants indoors” on your to-do list

By Carl Hoffman, University of Minnesota Extension

A recent drop of temperatures into the low 30s reminds us that it is time to move any houseplants that were outside for the summer back indoors. Most houseplants originated in the tropics and will not survive frost and actually have trouble coping with nighttime temperatures in the 40 degree range.

The first step to successfully returning houseplants to the indoors is to inspect them carefully for pests and diseases. That hibiscus plant that suddenly has an infestation of aphids did not generate the insects spontaneously; there were a few adults or maybe even just eggs that hitchhiked indoors with the plant. Insects and mites that entered the home with plants will multiply quickly in the warm, dry indoor environment.

While still outdoors, wash the plants with a fine spray from a hose. If you see any pests, treat them with a houseplant insecticide, insecticidal soap or even a weak solution of ¼ teaspoon of mild dish washing soap and water.
When using any insecticide be sure to check that the plant to which you are applying the product is listed on the label. Rather than risk spreading the pest to other houseplants, you might choose to discard any severely infested plants.

Don’t forget to check the bottom of each pot and the soil surface for slugs, sowbugs and beetles or other insects that may be hiding there. Keep plants that spent the summer outdoors isolated for two or three weeks so that you can keep an eye on them and treat any problems that may develop.

Yellowing of leaves and leaf drop is common when plants are placed in the lower light levels and drier environment found indoors. Place the plants where they will receive as much natural light as possible and even supplement natural light with artificial light to prevent leaf loss. If possible, slowly acclimate the plants to the lower light levels.

Because they are not subjected to the warmer temperatures and drying winds that occurred outdoors, growth will slow down and they will need less water. Water them when the soil at a depth of an inch or so feels dry. Watering plants on a regular schedule, as may have been done outdoors, will result in over-watering and the resulting root rot.

Plants that have been regularly fertilized outdoors will not need additional fertilization and should not be fertilized until new growth occurs next February or March. Fertilizing plants that are slowing down in growth will not only be a waste of the fertilizer product, but also place additional stress on the plant. Plants that are kept under artificial light generally continue to grow and may require monthly fertilizing throughout the winter.

Plants that outgrew their pots may need repotting and overgrown plants may require some pruning. Knock plants that are of manageable size out of their pots and check the root ball. If the root ball is so full of roots that it stands alone, it should be repotted. Remove the top couple of inches of soil in larger pots and replace with fresh potting soil. If it does not need repotting, but is top heavy, carefully prune the plant.

Hibiscus plants often put forth a lot of new growth during their summer outdoors. They can withstand fairly heavy pruning and, although you will remove some flower buds, they will soon generate new growth that will produce flower buds if indoor light is adequate. Standard (tree form) hibiscus should be pruned only enough to maintain the round shape.

If you have not started to bring your houseplants back indoors, put it on the top of your “to do” list.

(Carl Hoffman is an educator with the University of Minnesota Extension — Stearns and Benton counties.)