During the annual Chelsea Flower Show, which takes place in London in late May, the whole city seems on holiday. The streets are strewn with pink chestnut blossoms; Chelsea's traffic is backed up for blocks. Abandoning their cabs, distinguished couples dressed in tweeds are thrust into the midst of fuschia- and turquoise-clad teenagers and young fathers adroitly maneuvering baby carriages. In Sloane Square, great streams of people pour from the Underground, joining the parade surging toward the grounds of the Royal Hospital and the show.
Chelsea, the world's largest and most renowned flower show, is also a fine opportunity to put the final touches on a itinerary for a tour of England's gardens. But if your vacation is at an entirely different time of the year - or if it is roses you are most interested in and you must go in late June to see them - there are other sources of information.
A tremendous help in selecting which gardens to visit is ''The Shell Guide to Gardens'' by Arthur Hellyer. Its 67 pages of readable history on four centuries of English gardens will be invaluable in making sense of a sometimes confusing assortment of styles and periods. Available by mail order from David and Charles , North Pomfret, Vt. 05053, the guide costs $12.50 plus $1.25 postage for the first book and 25 cents postage for each additional copy.
If your vacation is limited to a week or 10 days, confine your garden hopping to certain areas, such as the Cotswolds or Kent. Both areas are so rich in large public and small-scale private gardens, it is entirely feasible to pick your gardens as you go along, but I'd strongly suggest working out a basic itinerary of well-known, frequently open public gardens, including those owned by the National Trust. Then, when time allows, you can fill in your schedule with smaller and lesser-known private gardens. Here you will often have an opportunity to talk with the head gardener or the owner, both of whom have had an active hand in creating it. Open times are various; check before going.
The single most important source for organizing a garden tour is a publication called ''Historic Houses, Castles, and Gardens.'' This guide not only lists ''most habitable properties open to the public,'' but includes directions, hours, admission charges, accessibility for the handicapped, restaurant facilities, and any other information you might need. The guide, which is updated yearly, is $4.75 from the British Travel Bookstore, 680 Fifth Avenue, New York, N.Y. 10019.
Another book that you might want to include in your order is ''AA Guesthouses , Farmhouses and Inns in Britain.'' At $6.95, it offers 3,000 recommendations for economical places to eat and sleep.
Bed and breakfasts range in price from $7 to $11 a night for clean and often pleasant accommodations. While some were merely adequate, others were set in lovely gardens or picturesque suroundings.
If you would prefer to stay at hotels, they should also be booked ahead. For part of my tour, once outside of London, I stayed in two hotels: one an old coaching inn, now a hotel-motel, the other, a kind of old-fashioned country hotel, both properties of Trust House Forte. With an extensive chain of hotels all over England, THF can easily be booked by phone in the US and charged to various credit cards.
For ahighly personal program of accommodations there are a number of organizations that offer an opportunity to live with the English in their homes. (See end of article for details.) It was At Home Country Holidays that arranged one of the most pleasurable stays of my tour at Muncaster Castle in Ravenglass, Cumbria.
Driving your own car will give you access to the gardens you want to see. Many gardens are simply not within easy reach of public transportation or Britain's extensive rail system. If you don't envision yourself driving, there are a number of guided tours available that will organize everything from air travel to accommodations to the selection of gardens. (See end of article.)
In your order from the British Travel Bookstore, you will want to include a road atlas. Among the best is the 34-page AA Great Britain Road Atlas. The AA atlas is clear, detailed, easy to read, and costs $17.25.
While many English gardens are still private, many are the property of the National Trust, a nongovernmental organization supported by public and private contributions. Before you leave the US, a membership can be obtained for $25 through the trust's American branch, The Royal Oak Foundation, 41 East 72nd Street, New York, N.Y. 10021.
Clothes for a garden tour should include warm wool sweaters, rain gear, umbrellas, tweed skirt or wool pants, and jackets, as well as lightweight cotton trousers and shirts for warmer days and, for both sexes, waterproof boots and ''sensible'' walking shoes. And don't forget a waterproof case for your camera and film.
If I were to sum up any suggestions for a successful garden tour, it would be that no matter how many gardens you visit, allow time for each to unfold its own special qualities. As Richard Staples, head gardener of Heaselands in west Sussex, explained to me: ''Sometimes a bus load of people will arrive to see the gardens and expect to see it all in 20 minutes. Now, how can a garden that takes years to develop, nurture, and bring along be seen, no less appreciated, in that space of time?'' ? $Kractical$A information Accommodations:
Write British Tourist Authority for information at 680 Fifth Avenue, New York , N.Y. 10019.
At Home in England, 68 Larchmont Avenue, Larchmont, N.Y. 10538 (914) 833-0175 . Stay with English family, $33 to $45 a night with breakfast.
Homestay, AAD Association, Box 3927 Amity Station, New Haven, Conn. 06525 ( 203) 387-4461. A ''meet the British'' experience. Minimum 2 nights, rates $13.25 to $16.50, depending on length of stay.
At Home Country Holidays, Bill and Gretchen Stevens, Arundel Holt Court, Bedham, Fittleworth, Pulborough, West Sussex. Telex 87612 Coxbus. Very personal style service, private suite $55 to $85 per night. Weekly rates available. Guided tours
Send for brochures to:
S&D Tours, 416 Hancock Street, North Quincy, Mass. 02171. (617) 696-3851.
Serendipity Tours Inc., 3 Channing Circle, Cambridge, Mass. 02138 (617) 354- 1879.
Garden Tours, 1150 Fifth Avenue, New York, N.Y. (212) 860-8429.
American Horticultural Society, Mrs. Dorothy Sowerby, Mt. Vernon, Va. (703) 768-5700. Periodic tours to England spring and fall.
Tours run in the range of $2,000 a person. This article follows up on last week's piece outlining a garden tour.