Every picture needs a frame. Garden edging is important: It frames flower beds, sets them apart, and gives them style, character, and contrast. It also marks transitions. In any garden, edges deserve careful attention.

Gardeners draw the fine line between flower beds and the rest of the garden in many ways. A line of bricks set on end, often angled so it looks like a fluted piecrust, makes a crisp edge around a bed. A row of smooth stones, a low, clipped hedge of boxwood, or a lush border of liriope all mark an edge and add still more form, color and texture to a garden composition. The careful definition of beds does not limit your imagination — it helps you organize your plants and your ideas.

Crisp, straight edges cut into a lawn with a sharp spade are perhaps the simplest edge of all. Such edges help keep weeds from creeping into your beds, and they are easy to refresh with a few quick cuts. Cut edges also give the gardener the flexibility to change the size and shape of the bed as the garden grows.

Garden designers like to use edges to emphasize contrasts and also to show off handsome materials. Joe Hertzler, a garden designer in Williamsburg, Va., surrounded the Colonial revival garden in his front yard with a traditional white picket fence. The bluestone walk to the front door creates two sharp edges of its own. It is lined with daylilies and colorful summer annuals, and it changes through the seasons as a tapestry of flowers and foliage grows and blooms. There is no room for grass.

In Hertzler’s front yard vegetable garden, bricks set on their sides edge beds of flourishing tomatoes, squash, eggplants and peppers. Even in high summer, the neat line of bricks separates the beds and the brick paths. On the other side of the front walk, in the perennial garden, it’s just the opposite: Creeping thyme and exuberant ornamental grasses are allowed to spill over the edge of informal flower beds onto stepping stones, softening the line between paths and beds.

In small spaces, where details really count for a lot, the edging itself may be very decorative. On a whim, a gardener in Madison, Wisc., used phonograph records she found at a thrift shop to trim the edges of her flower beds. Such idiosyncratic edging has a tradition: Upside-down wine bottles edged the beds in more than a few old- time gardens. Marla Galetti, a Kansas City gardener with an eye for unexpected details, used upside-down terra-cotta pots along the edge of a flower bed in her cottage garden; in another area, she defined the border between the grass and the flowers with bamboo canes cut to about eight inches in height.

Many Victorian-era ideas and materials still look good today: Antique terra-cotta or glazed ceramic edging tiles are a hot item on eBay, and occasionally turn up at estate sales and flea markets. You don’t have to buy antiques to replicate the period’s decorative touches, however. Garden shops and the gardening departments at big-box stores sell wire edging panels and sections of low wattle fence made of woven willow twigs, inspired by Victorian designs. They’re not practical for edging around a large flower bed, but, like the ruffle on a sleeve, they can be the finishing touch in a spot where you want a pretty detail.

Even the most carefully defined edge tends to lose its crispness in the growing season, when flower beds are full. Keeping short plants at the front of the border will help maintain order, but don’t be too quick to shear plants stretching across the edge of a flower bed.

Piet Oudolf, the Dutch garden designer and plantsman, likes to include some gracious taller plants along the edge to give a garden a naturalistic and spontaneous character. Oudolf appreciates geometric forms and uses them to great effect in his designs, but bending the rules, particularly along an edge, can make a garden much more exciting. Once you know where the lines are, it’s all right to blur them a little bit.