PHILADELPHIA — This summer, there must have been a dozen patches around the tiny borough of Narberth, Pa., sporting huge sunflowers.

It was no accident. The supersize sun-lovers were grown from seeds swapped among neighbors earlier in the year at Bob and Dawn Weisbord's house, as part of the Narberth Greens Flower and Vegetable Exchange.

"A big group of people came with lots of seeds," says Bob, who founded the exchange in 2008.

It may not be a new idea. But how neat is that?

At one time, collecting and sharing seeds was more about saving money than anything else. Today, it's likely to be that and more.

You might want to plant that great-tasting squash again next year, or preserve a hard-to-find plant. You might want to stand up for heirloom or older varieties, which are enjoying a resurgence.

Or you might be a gifted horticulturist like Gene Spurgeon, a retired architect, who enjoys the challenge of propagating hundreds of plants from seed (and the occasional cutting) for the Philadelphia area Hardy Plant Society's annual exchange or the Rock Garden Society's flower show exhibit.

Spurgeon, who's self-taught, works out of a rather luxurious "shed" he designed, along with his home, in Swarthmore. He collects seed for about 50 plants, among them carex, a carefree ornamental grass for shade, and unusual trees like Franklinia alatamaha, discovered by John and William Bartram in Georgia in 1765, and dawn redwood, which dates to prehistoric times.

"If I were a professional botanist, this would all be child's play," Spurgeon says, "but for someone outside that line of work, it's fascinating."

He adds: "It's also the pleasure of growing something you didn't have before, getting it into the garden, and walking your friends through and saying, 'I grew that from seed.'"

Seeds are collected when plants are finished flowering. They need to be washed, dried, labeled, and stored in a cool, dark place. Depending on the plant, seeds can be started indoors under fluorescent lights in late winter or sown directly into the garden in early spring.

Seeds, like plants, vary tremendously. They range from near-microscopic to jumbo jet, and come in every shape you can imagine — round, flat, big and fat or long and thin, with tufts, tails, wings.

Dawn Weisbord marvels at the oddball love-in-a-puff (Cardiospermum halicacabum), a fast-growing vine. Its three-sided seed pods look like pumped-up green lanterns; the little round seeds have white hearts on them.