Outside-in plants

Plummeting temperatures and early frost warnings forced many of us to scramble and bring our houseplants indoors. Because they are treated to lots of light and humidity, a summer outside helps most houseplants look robust and healthy. But making the transition to indoors in the fall can be hard on plants. Here's what you can do to help them make the move.

Clean, don't shine

First, clean your plants. Dusty, dirty foliage looks bad. Even worse, that layer of dust acts as a filter, which limits the amount of light that reaches the plants' green tissue, where photosynthesis occurs. Lukewarm water -- perhaps with a drop or two of mild dishwashing liquid added -- is all you need to wash stems and foliage. Plant shine products (including homemade concoctions of milk and mayonnaise) leave a residue that attracts more dust. And the unnatural shine they cause can reflect light away from the leaves.

Look for pests

Inspect your plants for signs of spider mites and other pests. You probably gave your plants the once-over when you brought them in. But it's easy to miss tiny eggs, which may develop in the warmth of your home. Look on the undersides of leaves and where the leaves join the stems, where insects are more likely to congregate. If you catch an infestation early, you may be able to control it by washing the plant with slightly soapy water or spraying it with insecticidal soap.

Repot if necessary

If your houseplant grew substantially this summer, you may need to repot it. Choose a pot that has a drain hole and is only an inch or two bigger than the original. Put a little fresh potting soil at the bottom of the pot, add the plant, then fill in with more potting soil between the root ball and sides of the container. If the surface roots have become exposed, add a little soil on top.

Go for sun

Find a bright location for your plants. Place sun-loving plants close to a south- or west-facing window. Low-light plants can be placed near an east-facing window. Be careful to not have your plants too close to the window, though. If they're right up against the glass, plants can get injured by the cold air. You should be able to lower shades or pull drapes to protect houseplants from the cold at night.

Water right

Poke your finger into the soil to determine if your plants are dry. Water thoroughly when the soil feels dry and allow excess water to drain from the plant. Don't let water sit in the pot plate. The water should be at room temperature or slightly warm.

Feed sparingly

Plants convert light energy through photosynthesis to make the "food" they need for growth and maintenance. Because light is limited in fall and winter, their need for fertilizer (think of it as a mineral supplement) is reduced. Apply fertilizer every six to eight weeks, but mix it at half the strength recommended on the bottle. When the days start getting longer in late February or early March, plants will start to grow more actively. Then you can fertilize your houseplants more regularly.

Put them together

Houseplants will look better when displayed in groups according to the amount of light they need. The small amount of moisture that plants normally lose to the air through transpiration will improve humidity when the plants are grouped. Large plants, such as ficus trees, palms or tall Norfolk Island pines, can stand alone in the house, just as they do in the garden.

Deb Brown is a garden writer and former extension horticulturist with the University of Minnesota. To ask her a gardening question, call 612-673-7793 and leave a message. She will answer questions in this column only.