Roy E. Smith of Falls Church writes that he has had problems with growing boxwood as a container plant. The leaves curl and are very brittle. He has moved it from direct sun to indirect light and has set the pot on a pebble tray, and nothing helps.

Boxwood as a houseplant likes as much as a half day of direct sunlight. Keep it cool - 65 degrees or less in the daytime and 40-50 at night. Possibly your apartment is too warm and also too dry. You should be able to keep it on the balcony in the summer time as it is an outdoor plant. Depending on the exposure, it may need some shading and will certainly need attention to watering if the container is very small.

Mrs. James B. Gregorie, Alexandria asks:

1. What causes the outer edges of some of the leaves of my Tolmeia to turn pale green or light brown?

2. One of my ruffle ferns, grown in bright light and kept evenly moist, turns dry and brown on the lower part of the fronds. What could be wrong? Another fern similarly grown is doing fine.

The damage to Tolmeia leaves sounds as if spider mites have been invading it. Spider mites live under the leaves; they spin a fine web. Wash the plant at the kitchen sink with a strong spray of tepid water to dislodge the pests. If the infestation is serious take the plant indoors and spray with malathion, after the spray dries, rinse the foliage with clear tepid water.

Examine your fern for scale. Pick off the scale with your fingers or brush it off with a toothbrush dipped in soapsuds. There is a multitude of insecticides that will control scale, but not all can be used on ferns. If the infestation is heavy, it is best to dispose of the plant.

Readers of the Indoor Gardener column frequently send leaves of plants with questions about disease or insect pests. It is practically impossible for the leaf of a plant sent through the mail to arrive incondition good enough for the problem to be diagnosed.

Take the leaf (or the plant) to the extension agent in your area. Extension agents are located in the District of Columbia and in adjacent counties of Maryland land and Virginia. Their offices can be located under District or county government headings of the Telephone directory. Also, watch for announcement of "plant conditions" to be conducted in Virginia and Maryland in April and May.

The extension agent will identify the pest and recommend appropriate treatment. Pesticides are poisonous and should be used with extrem caution, especially indoors.

A few recent questions, accompanied by plant samples, are answered in general terms as follows:

Thelma Marshall of Washington - The jade leaves were too far gone for dependable analysis.

Dorothy Williams of Washington - The marks on the leaves of the ribbon plant look like fingernail injury. The philodendron leaf had deteriorated too much for diagnosis. African violet leaves are often spotted by splashing cold water on them, by burns from fertilizer solutions or by fertilizer splashed up from the soil when watering.

Mrs. Cy Shelton of Alexandria - Scales are probably the greatest pest problem for ferns. They congregate along the midribs of fronds and leaflets. Pick off the scale with your fingers or brush it off with a toothbrush dipped in soapsuds. Few pesticides are registered as safe for use on ferns.

Carol Wellman of Arlington writes:

My floor terrarium has been plagued with insects. I discovered spider mites and eliminated them by spraying. Now I have discovered small flea-like insects hopping around on the soil, especially right after watering. I tried Ortho's Household Insect Control Spray and Ortho's Isotex Insect Spray but neither worked. I removed the remaining plants, washed their roots and transplanted them. Is there any wat to get the bugs out of all that soil and sand?

The soil in your terrarium appears to be infested with springtails, which are small, usually white insects that crawl and hop over the soil surface. They sometimes become plentiful in moist situations where there is much organic matter. Mostly they feed on decaying matter; they do not harm healthy plant roots. Allowing the soil to dry out will help to control them. It is difficult to do a neat job of spraying inside a terrarium. A Vapona Strip (Shell strip) can be suspended inside a terrarium for pest control. Vapona strips should be used with caution in the living quarters of a home.

DO NOT USE HOUSEHOLD INSECT SPRAYS ON PLANTS. They may contain formulations of chemical or "carrying" materials that can injure or kill plants.