Q: The temperatures are dropping. When should I bring my houseplants indoors?

A: Temperatures below 50 degrees can damage tropical houseplants. Ideally, house plants that spent the summer outdoors should have been moved inside weeks ago after gradually moving them to a shadier location before finally bringing them inside. This slow acclimation allows plants to reduce their growth rate in preparation for their new indoor winter home.

Many of us have been enjoying the first taste of fall weather and watching our favorite teams play football, and have just recently had to start bringing our tender tropicals indoors without much preparation. In response to the sudden change in environment, plants may exhibit yellowing and drop their leaves. While most house plants are tough and will recover in their new environment, occasionally, the drastic change can kill the plant.

Many house plants become dormant over the winter, which means they will need considerably less water. Overwatering is the leading killer of interior plants and may lead to root rot, stem rot, fungus gnats, yellowing and leaf drop. To avoid these problems, allow soil to dry completely between watering. If you aren’t sure if you should water, pick up the pot, if it feels light, you probably should give it a drink; if it’s still heavy, wait a week or more before watering.

Avoid wetting the foliage by watering from the bottom. Place pots in a few inches of water in a sink or tub until soil is thoroughly wet, allowing the plant to drain well before placing it back in the saucer or tray.

Forced-air heating creates dry conditions that most house plants dislike. Many plants thrive in the naturally warm and humid conditions found in bathrooms and kitchens. Spider plants, orchids, peace lilies and ferns are just a few that enjoy high humidity. Humidity can be increased by grouping plants together and placing gravel or pebbles in a saucer filled with water beneath plants, creating a “mini rainforest” without waterlogging the soil.

Many times, plants are not the only living things found in containers that have been left outdoors all summer. Be sure to inspect roots and the inside of pots carefully to avoid bringing unwanted insects and other visitors indoors. While the plant is out of its container, take advantage of the opportunity to scrub the pot with warm soapy water since pot sanitation is a key factor in helping to reduce disease and getting rid of unwanted critters.

Most houseplants are not picky about the time of year they are repotted, so if your plants have outgrown their containers, move them to a slightly larger container before bringing them inside. Choose sterile, soil-less potting media that does not hold excess moisture. Media that contains a slow-release fertilizer is a good choice, but avoid using extra liquid fertilizers until spring.

This is also a great time to wash leaves to remove dust and improve the ability to capture all available light. If your windows are dirty, wash them inside and out to allow maximum sunlight indoors. Groom plants regularly by removing dead or diseased leaves and flowers and prune back leggy or unruly plants.

If you are thinking about buying new house plants this winter, consider air quality as you make your purchase. Research conducted by NASA found that specific plants remove toxic gases such as benzene, formaldehyde and trichloroethylene from the air inside space capsules as well as homes and offices.

These three compounds are found in man-made building materials used in newer homes, offices and furniture. English ivy, spider plant, golden pothos, peace lily, Chinese evergreen, bamboo or reed palm, snake plant, heartleaf philodendron, selloum philodendron, elephant ear philodendron, red-edged dracaena, cornstalk dracaena, and weeping fig are considered the top plants for removing toxic compounds and improving air quality.

NASA reports that 15 healthy 6- to 8-inch houseplants can make a significant improvement in air quality in a typical 1,800-square-foot home. To read more about NASA’s research, go to www.extension.umn.edu/yardandgarden/ygbriefs/h110indoorair.html.

Calendar item

This is the last weekend to register for The Garden Gathering at Cypress Gardens. Registration for this one-day workshop for garden and nature enthusiasts ends Monday.

The program will be held 9 a.m.-3 p.m. Saturday at 3030 Cypress Gardens Road, Moncks Corner.

Focused on nature exploration and gardening, participants may enjoy hands-on workshops led by experts, lunch, free compost, plant shopping, the popular “Ask A Master Gardener” clinic and more.

Go to http://bit.ly/TvZo4I.

Amy L. Dabbs is the urban horticulture extension agent and Tri-County Master Gardener coordinator for the Clemson University Cooperative Extension. Send questions to gardening@postandcourier.com