Q. Mrs. Ethel Lanford, Berkeley Springs, W. Va.:

I hope you can help me with two problems.

My Rex begonia has one leaf left. The others gradually turned to black crisp paper and I broke them off.

The pot has been on a tray of pebbles and water. What happened? What do I do now?

I have a pineapple lily and have been unable to find anything about how to take care of it and how to get it to bloom.

A. Rex begonias like to rest during the winter. Perhaps you have been forcing your plant with too much water and fertilizer which it was unable to use. Excess fertilizer in the soil would cause brown paper edges of leaves.

Some varieties of Rex begonia are more likely to completely dormant than others. Some simply stop growing. Others lose one leaf after another in quick succession. Gently pinch the rhizome. If the rhizome is firm, let the plant rest; keep it warm and out of strong light. Water sparingly; do not fertilize. Repot and resume watering and fertilizing in spring when new growth appears.

Pineapple lily, Eucomis zambesiaca, an exotic looking bulbous palnt, is a member of the lily family which comes from tropical East Africa. The bulb is topped by a rosette of broad lance-shaped leaves to two feet long, bright shining spotted purple beneath.

The inflorescence is a stout stalk bearing sweet-scented, waxy-looking starry flowers about half an inch in size, greenish with a violet ovary; it bulbs are planted in the fall or in Februay. It is propagated by offsets.

Pineapple lily likes a warm environment - 62-65 at night and as much as 80-85 in the daytime. It requires maximum light - full sun. Grow it in loamy soil, when watering, drench thoroughly, then allow it to become dry. Water freely when growing. Once leaves have died down, keep it almost dry until the following spring. The fact that your plant has not bloomed suggests that you have not given it sufficient light or sunshine. Feed it during the growing season with liquid houseplant fertilizer such as Hyponex ar Rapid-Gro.

Herman L. Vinke, Bluemont, Va.:

I have a lot of house plants which are doing will except that they attract mealy buts.These creatures like especially gardenia, African violet, avocado and Jerusalem cherry. I clean them with a soft brush and spray with water and some chemical spray. Is there a better treatment?

A. You can spray your plants with a mixture of Black Leaf 40 in soapy water; follow directions given on the bottle.

Another remedy is the following: Use a mixture of 4 teaspoon dishwashing detergent in a gallon of water; add a weak tea made from cigar or cigaret butts; shake it well; place it in a sprayer that shoots a fine mist.

Several applications of spray may be required to get rid of the pest.

Do not use the Black Leaf 40, or tobacco tea, on your Jerusalem cherry.

If you have the patience, a good remedy is to dip a Q-tip or cotton swab in alcohol and touch each mealy bug or lift it off the plant.

Many indoor gardeners prefer to discard a heavily infested plant rather than risk damage to other plants.

Be sure that any chemical spray you use is recommended for the pest you are trying to control. Read the label and follow directions for its use.

F. Forer, Silver Spring:

My 2-year-old night blooming cereus is now 25 inches tall with lots of side growth in a 6-inch pot. I don't want it to get as large as the plant from which the original cutting was taken. What shall I do with it? Can it be kept small?

A. The night blooming cereus is a climbing or clambering cactus, reaching 25 feet if supported. There several means of restraining a plant which is naturally inclined to grow larger than you want it to be, namely, keeping it in a small pot, top pruning, root pruning, reduced fertilizing.

When top growth is making the plant too large or top-heavy, prune away some of the excess. In addition, reduce the amount and frequency of fertilizing. When the plant needs to be repotted, prune the roots, reducing the size of the root ball, and return the plant to a pot of the same size with fresh soil; at the same time, prune away some of the top growth.

Plant Show

On Saturday and Sunday the Potomac Valley Chapter, Indoor Light Gardening Society of America, will hold a plant show at the U.S. National Arboretum, 24th and R Streets NE (off Bladensburg Road).

In addition to the judged show, there will be educational exhibits and how-to information on all aspects of growing plants under artificial lights.

Show hours are 1-5 p.m., Sunday. There is no admission charge, and the public is invited to attend.