The National Capital Cactus & Succulent Society, and cactus and succulent societies from Maryland, Philadelphia, New York and New Jersey, have announced the First Eastern Cactus & Succulent Conference. This gathering, cosponsored by the Smithsonian Institution and the U. S. Botanic Garden, will include a Cactus and Succulent Plant Show at the U. S. Botanic Garden from 9 a.m. to 4 p.m. Saturday and from 9 a.m. to 5 p.m. on Sunday. The show will feature prize-winning plants from all over the country and will give the public a chance to see plants never before exhibited in this area.

The show will be open and free to the public. In addition to the show, lectures about cactus and succulents are scheduled from 8:30 a.m. to 5 p.m. Saturday at the Museum of Natural history, 10th Street and Constitution Avenue NW. Registration is required for the lecture series. For additional information, call Bob Stewart, 962-3228 during the day, 736-5508, evenings.

Reader's Questions

Elizabeth Odell, Washington: Can you recommend any printed material on African violets? Is there a place from which I can order a booklet? I have several varieties, some of which do very well in my north exposure. Some have a very heavy growth of greenery, which hides the few blossoms produced. Also, the root systems climb out of the pots.

A. Helen Van Pelt Wilson's African Violet Book (Hawthorn Books, $7.96) is a popular and authoritative reference. Perhaps you can borrow it from the city public library. Cultural leaflets are published by the African Violet Society of America Inc., P O. Box 1326, Knoxville, Tenn. 36901. Write for their list. "African Violets and Their Relatives" is the title of a handbook ($1.75 postpaid) published by the Brooklyn Botanic Garden, 1000 Washington Ave., Brooklyn, N.Y. 11225. It includes cultural notes.

If the roots of your violets are climbing out of the pots, they are apparently flourishing and need to be in larger pots. Try using a plant food formulated for African violets to bring about a balance between leaves and flowers.

Geraldine Wheeler, Hillcrest Heights: Would you send me information on how to cut back and re-root a dumbcane plant?

A. Dumbcane (Dieffenbachia) can be rooted in water. Cut off the top of the plant including about 6 inches of the cane and put it in a bottle of water, keep it in bright until roots form. Then it can be planted in your regular potting mix. The stub of the plant that is left in the pot should send out new shoots if you give it your customary care of moderate watering and bright light.

If your plant has become excessively tall - that is, if it has a long, leafless stalk - cut off the top and root it in water as above. Then cut other pieces of the cane in 3-inch or 4-inch lengths to use as cane cuttings.

There are two ways to roots these cane cuttings.

1. Stand the cutting on end in moist sand or vermiculite, setting it about two or three inches deep. When clumps of new growth are three or four inches across, pot the plant in your regular potting soil.

2. Lay the cane cutting horizontally, half buried in rooting medium. Cover the container with a plastic food bag to retain moisture and set it in bright light, but not direct sunlight. If there are several joints on the piece of cane, several shoots should develop. When the shoots are two inches tall, cut them off and set them in rooting medium to let roots develop. Again cover the container with plastic until growth of shoots indicates that rooting has occurred; then pot the new plants.