Melanie Ruckle at her Putnam Hill Nursery in Forest Hill, Md. Stone walls built by her husband, Keith Holt, form terraces for potted plants. (Adrian Higgins/The Washington Post)

At some point in a gardener’s life, you realize that you will never have enough room to plant everything you’d like to and, moreover, you will never live long enough to discover all the fabulous plants that are out there.

This is the whole allure of the enterprise — each growing season promises the thrill of discovering a new plant. New to you, that is; you don’t have to explore the Amazon jungle to find an undiscovered species, just that giant coneflower or maidenhair fern you never got around to planting.

Often, new plantings come with changing conditions. Encroaching shade in part of my garden forced a major reworking and resulted in a pleasing assortment of plants that do well out of full sunlight: hostas, ferns, epimediums, hakone grass, loropetalum, spirea and others.

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On the sunniest end, I planted maybe a dozen cranesbills of the popular variety Rozanne. Rozanne blooms its head off, with pretty, violet-blue single flowers, about an inch across, but it suffers for its art, generally growing more feeble after two or three years. The resulting gaps in the bed had been bothering me for a while, but I didn’t know what to replace it with, except that it would be with a mix of perennials that would play off one another.

Then I remembered Melanie Ruckle, whose Putnam Hill Nursery is a cherished source by my discerning garden friends. Ruckle is a familiar presence at spring and fall plant sales at botanical gardens throughout the region, but her two-acre nursery in Forest Hill, Md., is also open to visitors and Internet shoppers. She lives there with her husband, Keith Holt (he's a sculptor).

Their property in Harford County is quite narrow and long. Two old, majestic sycamore trees mark the upper reaches, but the land has changed in their ownership from a long grassy slope into a series of terraces formed from dry-laid stone walls, crafted by Holt.

Over the past 22 years, they have formed the sort of family-owned enterprise that seems so rare these days, as retail nurseries have devolved either into the outdoors section of mass merchandisers or large-scale independent garden centers. And yet for Putnam Hill Nursery, “mom and pop” seems so incorrect a label because Ruckle’s stock reflects a deep horticultural knowledge and sophistication. Most of the plants are propagated in the greenhouses on site, either by seed or cuttings, and this approach is rare in itself. Many retail nurseries may have little to do with the growth of the plants they sell, and the horticultural trade is remarkably byzantine with plants (including trees) going through a series of growers before reaching the consumer.

Ruckle’s approach allows her to find more uncommon plants to reproduce for her customers. In the propagating greenhouse, I came across a tray of robust seedlings of the native Indian pink, a woodland plant with striking clusters of red tubes opening with a yellow flare. The seedlings were from seed collected last summer and will be big enough for sale next year.

For Ruckle, this is a plant that has it all, but she noted it does take until May to emerge. This would make it perfect for pairing with spring bulbs, we decided.

I feared my site would be too dry for Indian pink, and so I fed my galloping mania for salvias or ornamental sages. Finally, the wispy three- to four-foot Salvia reptans West Texas Form has a place in my garden. Like a lot of sages, it blooms late and provides great fall ornament for the gardener and sustenance for bees and hummingbirds. Its slender stems are covered in cobalt-blue blooms, akin to the stalks of perovskia. Next came the meadow sage (Salvia azurea grandiflora), which is similarly tall and narrow-leafed but with big, blowsy blooms, a strong, clear blue.

In the shadier parts of my cranesbill bed, I decided to plant a couple of Japanese woodland sages, the first Shi Ho, a variety of Salvia glabrescens. This is a solid but compact perennial with large arrow-shaped leaves and big purple blooms that appear in the fall. The other is a closely related sage from Japan, Salvia koyamae, but with soft yellow blooms. In her " Book of Salvias ," Betsy Clebsch wrote that "here is a plant that can easily be tucked into an existing shaded border. In time it will weave itself through and around established plants, making a handsome cover." Sounds just the ticket.

In keeping with this theme of an autumn garden, I asked Ruckle to show me some asters that might take a little shade. The obvious choice might have been the white wood aster, handsome as a woodland native when planted in and around other perennials. I was drawn, though, to a couple of more unusual varieties of a Japanese aster, Aster ageratoides. Both are upright and a little stiff-looking, but they spread by stolons to create drifts that, I read, are smothered in daisies in October and November that are perfectly frost-hardy. Ezo Murasaki is bright pink with yellow centers; Ashvi is a white version.

I hadn't grown ajuga or bugleweed for many years, seeing it as a bit coarse, but I discovered that I just wasn't looking hard enough. Chocolate Chip is a popular ground-hugger that had passed me by. It's remarkable for its narrow (for ajuga) leaves with bronze tints. The effect is of a fine-textured, creeping ground cover for those awkward spaces that need cover but not show.

I bought a couple of ajuga-crowded four-inch pots and, once home, managed to extract almost 40 plants from them, which were then planted over an area of about six feet by two feet. Spaced six inches apart, the little divisions will form a single mat in no time.

Ruckle said she is driven in her plant selections to give gardeners perennials (there are a few shrubs) that are different, and those that aren’t conspicuously decorative contribute in other ways, perhaps by being easy to grow or vital to wildlife.

The Dutchman's pipe (Aristolochia macrophylla) is a dense vine with heart-shaped leaves whose rapid growth was used to screen and shade sleeping porches in Appalachia. The blooms are no match for the ornament of the several tender species of Dutchman's pipe, but the hardy one has one endearing quality in the wildlife habitat garden. Ruckle took me to an established plant to study the well-eaten leaves. There was a healthy population of caterpillars of the pipevine swallowtail. The butterfly's larvae are black, knobbly and red-spotted. Soon, these crawlers will turn into an imposing dark butterfly, black with iridescent blue hind wings.

There is now a young vine sitting at the base of my vegetable garden arbor.

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