"A miniature garden is not just a garden with small plants. It's all about scale," says Sullivan, 47, a Penn State grad who fled the business world in 2007 to study horticulture and hort therapy at Temple University Ambler.
Meaning that the design's highest point should be a little taller than the pot is wide - and that everything in the garden should be proportional.
It can be planted in all kinds of small vessels - troughs and deep dishes, terra cotta pots, and glazed or plastic containers, as well as tiny wheelbarrows and wagons, gourds, tin tubs, and birdbaths.
Sullivan likes to use wooden clementine crates from the grocery store, decorative bowls and baskets, adding the drainage holes herself.
Her "potting shed" is the kitchen island or screened-in porch at her Fort Washington home. Here she fills a 14-inch-diameter container with potting soil, pebbles, and greenery - a 15-inch arborvitae that can go outside later, a dwarf hosta, ground covers Ajuga reptans and Sedum reflexum pulled from the yard, and moss from an accessible corner of the roof.
Sullivan, "the child of two hippie gardeners" from Newtown Square, points out that miniature gardens require no bending or digging, no heavy hoses or bags of mulch to lug around.
And sure, you can spend a small fortune on accessories, like a patio set of four metal chairs, table and umbrella for $29. Or you can do what Sullivan does, which is make your own from recycled and found materials.
"Take two pieces of bark and boom! You have a bench or a little table," Sullivan says. "Thread a red cotton string through a dried avocado shell from the compost pile and boom! You have a tree swing."
Turn that datura seed pod into a lamp, small bowl of water into a pond, votive candle into a fire pit. Ever see a champagne cork become a chair?
Sullivan readily moves her mini-gardens from kitchen to dining room to indoor porch. In warm weather, they're an inviting addition to the outdoor patio or garden, which looks as happy and informal as its designer.
She rarely puts figures, human or otherworldly, in her gardens, but plenty of folks do, including the fathers and sons who attend her workshops. They like to embed manly dinosaurs in their landscapes.
"It's a magical world of your own making," Sullivan says.
Garden writer Betty Earl of Naperville, Ill., became so enamored of the tiny tableaux she was seeing in private gardens, she wrote a book: Fairy Gardens: A Guide to Growing an Enchanted Miniature World, published this year by Betty Mackey, of B.B. Mackey Books in Wayne.
"Over the years," Earl says, "I noticed these tiny little containers that had had a couple of plants in them and maybe a little chair were getting a little bigger, with fancier, more interesting accessories in them.
"Miniature gardens are like doll houses for adults in the garden," she says.
The doll-house aspect may be why far more of those adult fans are female.
"I think when any of us women look at little tables and chairs and Victorian wrought iron, it's like we're a child playing with these toys again," says Earl, who hopes to launch a website/blog called fairyandminiaturegardens.com Dec. 1. She's also thinking about doing a book on miniature gardens for holidays and special occasions.
And no wonder.
Holiday decorating in this country has taken off, the mini-accessory makers have more products available than ever before, and the nursery industry is pushing out dwarf and mini-varieties of everything from ground covers and grasses to shrubs and trees.
For years, Mackey has enjoyed planting small-scale rock gardens and making her own papercrete (paper and concrete) troughs. She finds that the smaller landscapes engage the viewer in ways bigger ones can't.
"People might think, 'Oh, what if I were only 2 inches tall? I could sit on that little chair and it would be so wonderful.' "
By nature, Mackey says, she's "drawn to anything that involves folklore and imagining and fantasy, and I just naturally love all bell-shaped flowers and little mushrooms and moss, tiny stumps and ferns and hidden nooks and moisture and anything blue."
Kathryn Newman, who opened the Miniature Garden Shoppe (miniaturegardenshoppe.com) in Brimfield, Ill., in 2008, says a lot of her customers are traditional gardeners looking to try something new. "You can't totally re-landscape your yard every year but you can make a whole new garden with tiny containers," she says.
Then there are people with no space or yard, and people with space but no time.
Calls come regularly from retirement communities and nursing homes, too. "People are interested in a way to get your fingers dirty without breaking your back," says Newman, who studied horticulture at the University of Illinois.
It's not just backs and knees that motivate Sullivan, who likes to nudge her husband, Terry, a vascular surgeon, and their two teenage daughters into the kitchen for a session of miniature gardening.
"It slows everyone down. Stress just disappears," she says.
Brenda Sullivan explains why miniature gardens are so popular now. www.philly.com/ginny
Contact Virginia A. Smith at 215-854-5720 or email@example.com.