Plants make a welcome addition to the home or office. But did you know that houseplants could actually clean the air?

Studies by the National Aeronautics and Space Administration have shown that plants can reduce the levels of some common indoor pollutants like formaldehyde and benzene.

Here are a few good tips for choosing and caring for your natural air filters.

Start with healthy plants. Check the leaves both top and bottom for insects. Also look closely in the place in which the leaf joins the stem. This is a great place for insects to hide.

Brown edges or spots on leaves can be an indication of too much fertilizer, too much heat or a disease problem. Look for plants with a uniform color. The lower leaves should not be yellow. Avoid wilting plants, and also those standing in water.

Consider the light. Most houseplants are considered high-, medium- or low-light plants. Generally, the brightest light in your house will be a south-facing window and the lowest light levels are to the north. If you can cast a shadow with your hand, you can grow a low-light plant.

Because light often strikes the plant from only one side, rotating the plant will help to maintain an upright growth habit. Typically, plants with variegated foliage and flowering houseplants require higher light levels.

Beware of temperature extremes and drafts. Plants vary in their requirements, but generally temperatures between 65 to 75 degrees Fahrenheit are suitable.

Keep in mind that night temperatures may be much lower than those in the daytime, and windowsills may get very cold. Avoid heat ducts and doors opening to the outside air.

Use the proper soil when you repot. Artificial soil mixes are the best for general houseplant growth. Mixes high in peat moss with the addition of perlite allow for proper drainage and good aeration for plant roots. Better quality soils are sold by volume, not by weight.

Special mixes are recommended for orchids, cactus and Africa violets. Pots for plants should always have drain holes. Repotting should be done when the plant roots begin to grow through the holes or when the plant becomes top heavy.

Increase pot diameter by no more than two inches to prevent any overwatering problems, and be sure to loosen the existing roots from the ball before transplanting. This will enable the roots to spread and become established in the new pot.

Monitor for pests. Occasionally, insects may be a problem. Common plant pests may include mealybug (white and cottony), aphids (small insects which can be green, black or brown), scale (an armored bump on a leaf or stem), mites (silvered foliage and/or webbing), and whitefly.

These insects can often be controlled or prevented with a weekly misting, or washing with insecticidal soap. Heavier infestations may require a pesticide, but you must know what insect is causing the problem before you can treat it. Sometimes, disposal of the plant is the best solution.

“Growing Green” is contributed by Lehigh County Extension Office Staff and Master Gardeners. Information: Lehigh County Extension Office, 610-391-9840; Northampton County Extension Office, 610-746-1970.