The Grounded Gardener: Be prepared for the perennial that checks out early

Buy a perennial, plant it up, and for at least three years, you'll have good luck -- because that's the definition of a perennial, a plant that lives at least three years in the garden.

So if your perennial dies after just a year or two, is it your fault?

Not necessarily, says Bob Lilly, Seattle-based perennial broker and co-author with Carrie Becker and Susan Carter of "Perennials: The Gardener's Reference" (Timber, 536 pages, $49.95). Lilly says some plants we consider perennials don't last as long in the garden as we might expect.

Just because a blanket flower (Gaillardia) won't last for a decade doesn't mean you can't enjoy its quill-like petals in shades of gold and bronze. A short-lived perennial is no bad thing, as long as we are aware of its tendencies and plan accordingly.

Short-lived perennials that reseed make it easy to always have them in the garden -- sometimes, quite a few of them. Your personal tolerance for reseeding will govern just what you keep and what gets dug up.

Knautia macedonica, a pincushion flower similar to Scabiosa -- the gorgeously dark Scabiosa atropurpurea is itself not too long-lived -- grows from a basal rosette of leaves. It looks unassuming over the winter and into early spring, but then takes off with long, thin, branched stems of maroon flowers.

The flowers appear throughout summer and if not deadheaded, more plants show up the following year, replacing the oldest plants, which die out. This, Lilly notes, makes them seem like a perennial.

The seedlings are not difficult to dig out, and the only complaint I have is that one has come up in the middle of my variegated feather reed grass (Calamagrostis x acutiflora 'Overdam'); that one is not easy to dig out.

Cupid's dart (Catananche caerulea), with its blue flowers for several weeks in summer, keeps blooming as older flowers set seed. A stand of cupid's dart may appear each year, but it may not be the same plant that started it all.

Sometimes it's where we put the plant that can lead to its early death. Cupid's dart needs full sun and well-drained soil; heavy soils can lead to a shorter life. That seems to be the case with other short-lived perennials. The sprawling Texas native Gaura lindheimeri, which comes in such cultivars as 'Whirling Butterflies,' 'Siskiyou Pink' and 'Pink Cloud,' also need full, hot sun and sharp drainage -- anything less can lead to its early demise, making it, too, a perennial that acts like an annual.

Not that there aren't perennials that do well in clay soil -- Bergenia, several hardy geraniums and Monarda are a few examples -- but often those that need good drainage won't do well anywhere else.

Wallflowers are another case. Older wallflowers, formerly called Cheiranthus cheiri and now named Erysimum cheiri, are easy biennials in the cottage-style garden -- flowering one year, setting seed and then new plants flowering the next (as you have yanked out the finished plants). They show up in a range of warm shades -- golden yellow, bronze, rusty maroon -- and don't seem to be as fussed about soil.

Shrubby perennial wallflowers, such as Erysimum 'Bowles Mauve,' 'Julian Orchard' and others, can be short-lived and especially in clay soil. My 'Julian Orchard' died out after two years in heavy soil, but I have a 'Constant Cheer' that bloomed wildly again in its third season, in a pot. We'll see what happens next year.

Short-lived though the shrubby perennials are, all it takes is perusing a few photos of 'Apricot Twist' or 'Wenlock Beauty' to know that when my 'Constant Cheer' does give up the ghost, it will be replaced with another lovely wallflower.

There are perennials that are just not hardy for us, but with intervention, they can last for more than a year. That includes the deliciously scented chocolate cosmos (Cosmos atrosanguineus).

At Chocolate Flower Farm on Whidbey Island (chocolateflowerfarm.com), Marie Lincoln has tips for overwintering chocolate cosmos; it's a tuber, so it can be lifted like a dahlia and stored in the garage. As dahlias do little until at least May, so chocolate cosmos is slow to take off in spring.

Occasionally, it's pests that do in the plants. Root weevils, Lilly says, can dispatch any of the fancy heucheras in no time at all.

Some perennials are short-lived here no matter what you do. Daisy-flowered Anthemis tinctoria, which forms a sprawling clump of fernlike foliage and comes in pale 'Sauce Hollandaise,' lemony 'E.C. Buxton' and creamy 'Susannah Mitchell.' I had the latter for a couple of years, and all seemed well. This year, however, it didn't show up for the party.

The genus Verbena, which includes fabulous annuals for summer pots, has a few perennial species, too. But perennial Verbena 'Homestead Purple,' hardy to zone 7, is easily lost after a year or so. To enjoy its ground-hugging, purple flowers every year, be prepared to replace it.

Forewarned is forearmed -- read up on the plants you get, and not just the tag that comes in the pot. Knowing that your beloved Agastache 'Apricot Sprite' may not appear for its third season will reduce your disappointment and give you time to think about a replacement plant.

Many perennials that don't last are fine garden plants, and as long as you are aware that they may not make it past the three-year mark, you'll be ready for a new look after enjoying the ornament they offer. For as long as they offer it.