There's something about a circle: They're a perfect fit in any garden.

Garden designers turn to circles to define spaces, frame views and break up the sharp lines of a garden. They change the usual geometry of a space and your experience of it. Circles are approachable, restful, cozy, embracing. Squares and rectangles are formal and businesslike; circles have no sharp points and are graciously accommodating.

Carving a circle into the design of a garden is surprisingly easy. With a stake and string, you can quickly trace out a circle of any size for a lawn, a flower bed or a patio. Then define it any way you wish. Kristopher Dabner, a garden designer in Kansas City, Missouri, sometimes uses several circles of different sizes in a single landscape, arranged in great overlapping arcs out from the door opening onto the garden. The first circle might be a brick or stone patio; the second, perhaps a step down in the landscape or a round sweep of lawn; and yet another, just to one side, might define a seating area around a fire pit. The shapes create movement, compelling you to step deeper into the garden from one circle to the next.

People have been fascinated by circles forever. The monumental ring of stones at Stonehenge, in England, may be 5,000 years old. The modern use of circles in gardens is also well-rooted in American garden design and history. The Danish landscape architect Jens Jensen, who settled in Chicago in the late 19th century and became one of the pioneers of the Prairie School of design, incorporated "council circles" in his gardens. A ring of low stone seating was a perfect spot from which to contemplate the natural world, Jensen felt.

Circles are democratic, Jensen said. Sitting in a circle, "there is no social caste," he said. "All are on the same level, looking each other in the face. A ring speaks of strength and friendship and is one of the great symbols of mankind," he wrote in his thoughtful book, "Siftings" (first published in 1939). The mythical King Arthur must have been thinking along the same lines with his famous Round Table of knights.

Council circles -- and story circles, as Jensen called them when they were in a school or a playground -- still have a place in gardens today. When the Chicago Botanic Garden added its spectacular, naturalistic Evening Island landscape, a council ring of stones was built at the highest point in the plan.

You don't have to have a council ring to experience the soothing magic of circles in a garden. Keep an eye out for the circles in nature: They are there in the shape of lily pads, in tree rings, in spiderwebs. The face of a sunflower is a magnificent sunny circle, and a dandelion seed head goes even further: It is a lovely gossamer sphere. The splash of a single raindrop in a puddle generates a mesmerizing pattern of concentric circles. A round birdbath on a pedestal captures the Zen of the circle in a brilliant disc reflecting the dome of the sky.

Dabner uses circles in playful ways, too. In one client's garden, he laid out a brick pathway punctuated with antique grinding wheels of different sizes. In a pond, he added a bubbling orb and floated glass globes on the surface of the water.

Circles fit easily into gardens of every style. Margie Grace, a garden designer in Santa Barbara, California, used bricks to define circles in a Spanish-inspired garden, with a decorative tile mosaic in the center of each. Agave plants grow in the middle of another brick circle.

Circles can be lifted up into the vertical plane, too. A landscape architect in Richmond, Virginia, designed a formal garden with a rectangular patio for one of his clients, but the garden is first revealed to visitors through a gate with a large round opening -- a moon gate. The circular frame around this glimpse of the garden imparts mystery and intimacy, coloring the whole experience of the garden. Partway along a brick path to the patio, a circular gathering space is defined by neatly trimmed balls of boxwood, echoing the circular motif.

Like the face of the moon, circles in a garden are soothing and compelling. The patterns they create may be playful or profound, and they're always just right.

(For editorial questions, please contact Clint Hooker at chooker@amuniversal.com.)

Alliums burst into glorious spheres of bloom in late spring, as jaunty and debonair as the season. Fall is the time to plant them by the dozens.

Alliums are flashy blooms by any measure. Their globe-shaped flower heads, covered with an uncountable number of tiny star-shaped blossoms, have tremendous impact in a garden.

"They really add an exclamation point," says Christian Harper, a horticulturist at Olbrich Botanical Gardens in Madison, Wisconsin, who has been planting alliums in Olbrich's flowerbeds for more than 20 years. "There is just something about those globes from a distance," he says, "they appear to be floating, and they really pop."

The allium family of ornamental onions is dominated by great big blooms. Mail-order specialists offer the widest variety, with a dozen or more different types in some catalogs. Garden shops often have a good selection of several different alliums, usually including Globemaster, the biggest of them all, which has 10-inch purple globes of sparkling flowers on stems up to three feet tall. Globemaster's flowers last for a couple of glorious weeks in the garden. After they bloom, the sturdy flower heads remain decorative for months -- at this point, they're tawny, not purple, but there's simply nothing else in the garden world quite like these big round balls, and they hold their own while the roses and daylilies come along.

Besides Globemaster, there are purple alliums with somewhat smaller orbs of blooms, white-flowering alliums, alliums with looser heads of pink flowers, and sunny yellow alliums only about 10 inches tall. Garden designers prize them all for their great beauty and for their ability to bridge the season. Like a burst of fireworks at the end of spring, alliums lead the parade of summer flowers like a tall drum major at the head of a marching band. The earliest-blooming types loom above spring's last tulips, and the latest to bloom open with the roses.

Have fun with them. "I have a favorite, and it is Allium schubertii," says Barbara Katz, a garden designer in Washington, D.C. "It's like a constellation." Allium schubertii is an atypical allium, growing on stems only about 18 inches tall. The globe of blooms, on the other hand, is about 12 inches in diameter. Individual flower stems are of several different lengths: The effect is distinctly starlike, twinkling madly.

Katz also plants "a ton of Purple Sensation" alliums in her own and clients' gardens. The dark purple blooms stand about 30 inches tall. "I mix it with hostas, and it looks like the hostas are flowering," Katz says. "I plant it around hydrangeas. It's fun."

Katz and other designers purposely plant alliums among perennial flowers and shrubs because the strappy allium foliage is usually fading when its flowers come into bloom. A lively garden covers up the tired leaves, so you can admire the spectacular flowers all the better.

Purple Sensation allium is well-known for more than its great flowers: Among tall purple alliums, it is the greatest bargain. You can buy 25 bulbs for less than $20. Globemaster bulbs often cost $5 or more apiece. Ambassador, a tall purple allium with flower heads about six inches in diameter, is another expensive one, with bulbs at about $6 apiece.

They're all worth the investment. Alliums are known for their ability to persist in a garden for years. "They're easy and long-living, almost like perennial plants," says Jacqueline van der Kloet, a Dutch garden designer whose deft hand with flower bulbs and perennials has led to international garden projects, including some at Battery Park in New York City and Millennium Park in Chicago. (Both are collaborations with the naturalistic Dutch garden designer Piet Oudolf.)

Van der Kloet included Purple Sensation and the drumstick allium, A. sphaerocephalon in her bulb plantings at the Lurie garden in Chicago. She especially loves the smaller alliums, including the white-blooming bride's onion (A. neapolitanum), which is sometimes used in bridal bouquets. Good plants to include with all alliums are "plants that are rather modest," she says, "so the alliums will add just that touch of extra that makes the combination perfect." She suggests planting them with ornamental grasses, gaura, lavenders, catmint and cranesbill geraniums.

To take full advantage of the whole allium season, plant species and varieties that will bloom over a long time. Plant them in clusters of three or five bulbs, scattered here and there in flower beds. Planted this way, "it really looks like quite a lot is going on," says Christian Curless of Colorblends, a mail-order bulb specialty company that offers 11 different alliums in its catalog. Curless says that he, like many garden designers, "think of alliums as a little bit 'in-between season' plants," but it's time to change that. They create a season all their own, and share it graciously.

SIDEBAR

ALLIUMS IN ORDER

Fall is the time to plant alliums. If you plant both early- and late-blooming varieties, the season will last for weeks, from late spring through early summer. Some are so inexpensive that you can plant them by the dozen. More expensive alliums tend to be the largest-flowering types: Try three or five together, and prepare to stand back and watch the show when they bloom. Deer and rabbits do not like them. Here are some suggestions from bulb experts.

-- Christian Curless, of Colorblends, the mail-order bulb specialists, says the earliest allium in his catalog is Purple Sensation, which blooms "on the heels of tulips." Next up is Gladiator, which grows 40 inches tall, followed by the white-flowering Mount Everest, then Globemaster. "Nothing else in our catalog blooms as long as Globemaster," he says. The flowers are sterile, which may explain the long duration of bloom. Ambassador is one of the latest tall alliums to bloom. Its season overlaps with pink Knock Out roses.

-- Barbara Katz, a garden designer and owner of London Landscapes in the Washington, D.C., metro area, loves Allium schubertii, Purple Sensation and Gladiator. Globemaster, she says, "is almost over the top." She also recommends White Giant, with white globes of bloom, and drumstick allium, A. spaerocephalon, which blooms in early summer. Katz plants alliums in odd-numbered groups in a garden, buying a dozen or so bulbs. "With 25 alliums, you can make a very strong statement," she says.

-- Dutch designer Jacqueline van der Kloet, who has introduced fresh bulb combinations to the traditional world of Keukenhoff in Holland and to great public gardens around the world, likes Allium zebdanense, a tiny allium that blooms in very early spring, and the bridal onion, A. neapolitanum, which blooms in early May in her own garden. Her favorites to grow in mixed perennial gardens are Allium christophii, A. schubertii, A. atropurpureum and the drumstick allium. She also likes the new allium Summer Drummer, which grows up to seven feet tall and blooms in summer, with two-tone purple-and-white flowers on a round flower head the size of a big baseball.

SOURCES

-- Colorblends, www.colorblends.com

-- Brent and Becky's Bulbs, www.brentandbeckysbulbs.com

-- Van Engelen, www.vanengelen.com

(For editorial questions, please contact Clint Hooker at chooker@amuniversal.com.)

LATE BLOOMERS AND REBLOOMERS: THE GARDEN IN FALL

The changing season comes with a promise of splashy colors -- not just in the tree foliage, but in the garden, too. In a well-diversified garden, annuals, perennials and shrubs keep working long into fall and make this the garden's most refreshing season.

Garden shops traditionally stock up with chrysanthemums and pansies in the fall. They're typically in bloom or in bud when you buy them, and they keep right on blooming through cool autumn days. The selection is impressive, but these plants do not have exclusive rights to fall color: reblooming and late-blooming annuals, perennials and shrubs can be the backbone of a fall garden.

"Reblooming is more than a buzzword among breeders," says Natalia Hamill, a brand manager for Bailey's nursery, which developed the Endless Summer series of non-stop-blooming hydrangeas. "It's one of the first questions people ask," Hamill says. "The retail buyer wants to know: does it re-bloom? This is a goal for any spring or summer blooming plant."

Breeders have responded to the demand with plants that look great in summer's heat but really sparkle in the cooler, shorter days after Labor Day. It's a pleasure to be in the garden during this season -- summer's lushness lingers on, while the heat fades away.

Professionals actually use two terms to describe plants that keep blooming. Rebloomers are plants, such as many roses, that produce wave after wave of bloom from late spring through frost. Knock Out roses are the best-known reblooming shrub roses, but there are many other disease-resistant roses that look great all season long and keep blooming through the fall, including two dozen roses in Bailey's Easy Elegance series. Reblooming plants produce their flowers exclusively on each year's new growth.

Remontant plants are those that bloom both on the previous year's growth and on new growth, Hamill says. In the world of hydrangeas, remontant types are the hottest thing on the market. The buds that open early in the summer have wintered in the garden; in late summer and fall, more flowers are produced on new growth. For gardeners, the terminology is less important than the flowers themselves. Bloom Struck, the latest hydrangea in the Endless Summer series, is an especially prolific plant: It continues to produce flowers until the end of October, even in Minnesota.

Clipping off the spent blooms of annual flowers all summer long will encourage them to keep blooming through fall. Cosmos and zinnias come to mind, but marigolds are hearty rebloomers, whose cheerful yellow-and-orange palette suits the fall season perfectly. They're often available at garden shops in fall, alongside mums and pansies, in case you neglected to plant them in the spring.

Cutting spent blooms to encourage a new flush of flowers also works with some shrubs, such as crape myrtles, Hamill says. "Cut them back after they bloom in summer, and they will rebloom in September and October," she says. The new Bloomerang lilac will throw up flowers through the fall if you cut off old blooms, with either hedge shears or hand pruners, and they add a fine color to the fall palette. Butterfly bushes also continue to bloom if you keep them trimmed.

Hamill loves reblooming and remontant plants, but she doesn't rely on them alone. Ornamental grasses are at their exuberant best in fall. Asters and sedums come into bloom, attracting butterflies to the garden. Of course, there are the chrysanthemums and pansies. Trees and shrubs with red berries are bright spots in any garden, and they also attract migrating birds. "You really want layers of plants," Hamill says, "with foliage, flowers, seed heads, pretty textures."

Among foliage plants, the handsome leaves of ninebark Amber Jubilee or Coppertina will bring the fiery colors of the maples down to eye level; the large, quilted foliage of oak-leaf hydrangeas turns from green to a rich burgundy in fall. Tiger Eyes sumac, known for its attention-grabbing chartreuse foliage all summer long, turns an intense, dramatic orange in fall before the leaves drop, exposing striking straight stems that cast long shadows in the winter garden.

If summer flowerpots are getting tired, early fall is a great time to replant; garden shops are usually well-stocked right after Labor Day. "It's time to spruce up anything that looks bedraggled," says Chris Brown, greenhouse manager at White Oak Gardens in Cincinnati. The garden shop sells ornamental grasses, anemones and asters for flower beds or for fall pots. Like many gardens shops, White Oak Gardens also stocks a good supply of trees and shrubs, and fall is the ideal time to plant them. For serious gardeners, "it's a shot in the arm," Brown says.

There's no reason to slow down: Fall is a great time to plant, and a beautiful time of year to be in the garden, says Tom Hilgeman, the shop's general manager. Hydrangea paniculata, whose creamy panicles of blooms fade to a rich, deep blush, is one of his favorite fall plants. He also recommends shrub roses and spireas for fall gardens. Shrubs you plant in the fall will not grow much before winter sets in; but water them well, and they'll send roots down and settle in. Next spring, they'll be ready to grow -- and to keep on looking good all the way through to the end of fall.

(For editorial questions, please contact Clint Hooker at chooker@amuniversal.com.)