The annual Bull Roast and horticultural show of the American Horticultural Society will be Sunday, May 1, noon to 5 p.m., at River Farm, Mount Vernon. Everyone is invited, according to the sponsor group's president, Dr. Henry M. Cathey, who is also chief of the florist and Nursery Corps Laboratory, USDA Agricultural Research Service, Beltsville.

J. Benjamin Williams of Silver Spring, hybridizer of Rose Parade, a [WORD ILLEGIBLE] that won an All-American award in 1975, will discuss new types of roses. Dr. James B. Shanks, University of Maryland professor of floriculture, will offer tips on growing hydrangeas.

Dr. Phil Parvin, from the island of Maui, will display his exotic collection of proteas. Jane Steffey, Carl Hahn and I will be on hand to answer gardening questions.

Henry and Marcy Gathey will distribute giant sunflower seeds to children and announce a contest to culminate Oct. 9 when the society will sponsor "Super Sunflower Sunday."

There will be a daffodil display sponsored by the National Capital Daffodil Society, and Red Senseation, a new begonia with the largest flowers of any wax begonia in the world, will be exhibited.

Dick Simon will demonstrate ornamental grasses; there will be a bog gardening session and a display of medicinal herbs.

A $2 per person admission fee (children free) will be charged. Bull Roast barbecue will be available for $5 per person (children under 12, $2.50).

To get to River Farm, go south on George Washington Memorial Parkway, pass the stone bridge overpass 3 1/2 miles south of Alexandria, and turn left at next exit to enter grounds.

George Washington purchased Clifton's Neck, 1,800 acres in disarray but with great promise, soon after he married Martha Custis, and renamed it River Farm. It became one of the five farms comprising his Mount Vernon Estate.

In 1973, the American Horticultural Society purchased River Farm (27 acres) with funds provided by the Enid A. Haupt Charitable trust. The society is in the process of becoming a national center for horticulture.

River Farm today is much as it has been through the centuries. The gently rolling Virginia landscape descends gradually to the river, great walnut trees shade beautiful lawns with two Kentucky coffee bean trees (perhaps planted by George Washington himself, a variety he introduced to the area). Plantings of boxwoods, magnolias, wisteria and other ornamentals blend into a setting of serence beauty. The historic dwelling is now the home of the society.