Don't neglect houseplants that have been set outdoors for the summer.

Summer sunlight and rain not withstanding, houseplants confined to pots still need to be fed. Ra-Pid-Gro and Miracle-Gro are two good water-soluble fertilizers to use according to directions on the container.

Since clay pots dry out rapidly, plants in those kinds of pots sometimes need to be watered twice a day.

Pots that have been set in the ground under shrubbery should be given an occassional quarter turn so that roots will not grow out the drain hole into the soil beneath the pot. Pots or baskets which are on patios or porches and receive most of the light from one side will need to be turned occassionally so that plants don't grow one-sided.

Cut off bloom stalks of coleus and pinch out growing tips of all branches to encourage further branching and bushiness.

Pick off faded flowers or dropped petals of Madagascar periwinkle. Side shoots of periwinkle can be removed with a sharp knife or scissors and rooted in water or a rooting mix to increase the number of plants. Pieces set in the soil around the parent plant will root and fill in the pot.

Prune tips of wandering Jews so the plants will continue to send up new growth from the main plant in the pot. Root the trimmings.

Hanging baskets made of moss and wire should be sprayed regularly or dipped in a moisture. It is next to impossible to remoisten moss that has dried out.

After a summer storm or days of steady rain, plants and pots may need some grooming. Empty water that has accumulated in saucers to get rid of silt or insects. Wipe or brush off splatters from plants and pots. Remove fallen tree leaves or twigs. Straighten up erect plants, blown over or weighed down by water. Remove faded or water-logged flowers and damaged leaves.

Watch out for invasions of insect pests. Pick or wash them off with brisk spray from the garden hose. Keep ahead of the pests so you won't have to resort to use of insecticides.

Most chemical sprays are basically for out-door use. Some may have serious side effects on houseplants. Read the label to learn the plant and pests on which an insecticide may be safely used. Apply only as directed. White Flies

Thunbergia, Fuchsia, Browallia - white flies love them. If the upper surfaces of the leaves have a grayish, spotted appearance, or if leaves are beginning to shrivel or dry, even though still green, examine the under sides. A cloud of minute white flies will arise because of this disturbance, and the under sides of the leaves will be populated with more flies or their offspring.

White flies are notoriously difficult to control, but mild infestations can be controlled with a soapy water spray. Mix one tablespoon of Ivory flakes per one gallon of room temperature water, or 4 teaspoons of dishwashing detergent per gallon. Apply as a fine mist on upper and lower leaf surfaces. Leave it on for two hours, then rinse with room temperature water.

Outdoors, a botanical pyrethrum-rotenone insecticide, such as Resmethrin, will subdue severe attacks of white fly, as well as of red spider mites, aphids and thrips.

One treatment may not be sufficient to eradicate the pests. Several treatments at weekly intervals may be needed to get rid of all adults and eggs. Vacation

When you go on vacation, place houseplants out of the sun or draw the shades, and water the plants thoroughly before you leave. Plants that are watered and drained the day before you leave can get along very well without water for three or four days.

If you go on an extended vacation, engage a plant sitter. Prepare individual pot labels or other written instructions to guide the sitter. If you have only a few plants, move them to a trusted friend's house.

For a short trip of a week or 10 days, plants that grow best in subdued light can be put in plastic bags. Set a stake or two in the pot to hold the plastic bags away from the plant's leaves.

The day before you leave water each plant thoroughly and let it drain. Cover the plant with the bag and tuck the ends under the pot, or slip the plant into the bag and close the top with string or elastic. Place baggedplants in a cool place without sunlight. Moisture given off by the plant will condense inside the bag, run down to the bottom and be absorbed in th pot and soil.

If you acquire any new plants during your travels, be sure to isolate them for at least a month when you get home. Such quarantine is recommended until you are sure that the new plants do not have unwelcome traveling companions such as insects and disease.