Experts on gardening will speak and answer horticultural questions at Oatlands' 10th Annual Garden Fair, expanded this year to three days, Sept. 28-30.

The plantation's 1803 mansion and four-acre English-style garden just south of Leesburg on Route 15 will be open for tours each day of the fair.

Admission on Friday is $25 a person, $20 for groups of 15 or more, and includes lunch and tours of the mansion and garden. Saturday's admission is $50 a person and includes lunch. Reservations are required by this Saturday. Sunday is family day and admission is $5 for adults, $3 for children ages 7 to 12 and free for children 6 and younger. Tickets can be purchased at the gate. Fair hours are 10 a.m. to 4 p.m.

Here is a lineup of the experts and a brief look at what will be happening each day:

Mary Lou Seilheimer, of Leesburg, moderates the Friday roundtable of gardening experts. Attending on Friday and Saturday are Cliff Glier, of Millwood, a rose specialist; Diana Nicholls, of Gainesville, an expert on Japanese and Siberian iris; Holly Shimizu, an expert on herbs; Harrison Symmes, of Blandy Farm in Upperville, a boxwood expert; and Michael E. Jackson, of Panorama Farm in Ashburn, an expert on woody ornamentals.

Also participating are Ronald Wade, of Stratford Hall Plantation, whose topic is espalier; Robert Goldie, of Dresden Farm in Middleburg, on cactus; Sally Bolton, of Middleburg, on flower arranging; Ronald Chiabotta, of Kensington, on lilies; Betty Flemming, of Leesburg, on herbs; Robert Alde, of Rockville, on roses; William Hoogaveen, of Middleburg, the gardener for Pamela Harriman's Willow Oak Farm and an expert on dahlias, tuberose and rieger begonias; Janet M. Skidmore and John Pierce, of Purcellville, on day lilies and hostas.

Marky Love, of Middleburg, hosts a flower arranging workshop for children on Sunday. Friday garden tours will be hosted by Oatlands horticulturist Alfredo Siani, Jenny Sherman, of Bluemont, and Karen Mazza, of Wheatland.

On Saturday, Italian Ambassador H.E. Rinaldo Petrignani and his wife are honorary patrons of "Gardener's Day;" the Capital City Croquet Club will hold a demonstration of six-wicket English croquet; and the Piedmont Driving Club will show off carriages and driving techniques. Sunday will include police K-9 corps demonstrations, woodcarvers, doll house displays, a food concession and a croquet exhibition.

For information, call (703) 777-3174.