SOMETIME during the last 10 years ordinary gardening metamorphosed into ''outdoor living,'' a phenomenon that grew like kudzu and engulfed everything from garden magazines to discount retailers. The trend continues to flourish, yielding an impressive annual harvest of new garden gadgets, furniture, décor and clothes from every corner of the world.

Outdoor living is subject to the same ''in-out'' cycles as décor and apparel. In some gardening circles it might be extremely embarrassing to be stuck with last year's stylishly rusty Victorian urns when all the neighbors are investing in this year's outsize cobalt blue olive jars.

One of the most fashionable garden accessories right now is the Witchety Woodland Tinkling Toadstool, which comes from England, garden capital of the western world. Less obvious than a lawn gnome and considerably more subtle than a grouping of pink flamingos, Tinkling Toadstools add color and sound to beds and borders. Available in three sizes (11, 16 and 21 inches tall), each toadstool consists of a glazed pottery cap, which is available in several colors, and an unglazed stem that is tapered on both ends. To plant the toadstools, all you do is insert the stems securely in the ground and hang the tops on them. They chime softly when the wind blows.

Deer are Public Enemy No.1 in many gardens, but birds are in vogue. The garden magazines are full of advice on how to create backyard bird habitats, which invariably include birdbaths. They are made of materials ranging from glass to copper to cast concrete. My new birdbath is a simple footed vessel of white porcelain that is about 12 inches wide and about 4 inches high. Intended for use in temperate weather only, the birdbath can be placed on the ground or in a garden bed surrounded by ornamental plantings. Two white porcelain birds are permanently perched on the edge of my bath, and from a distance it looks like a garden antique. So far the response from birds, the resident cats and the neighborhood groundhog has been positive.