I had a friendly debate the other day with a fellow professional gardener that might have devolved into a heated argument if I hadn’t capitulated. We were talking about one of my favorite plants, African blue basil, which she described as an annual. I call it tender perennial. To-may-to, To-mah-to? It comes down to semantics.

What is an annual? The definition I use was written by botanists who base it on a plant’s life cycle. An annual is the sort of plant that grows, flowers, sets seed, and dies all in one growing season. My friend’s definition swings a bit wider to include anything that won’t survive winter in our gardens. I yielded the point because she’s not alone. You won’t find African blue basil in the perennial section at any nearby nursery.

But this is where it gets tricky and why I’m having trouble letting go: I bought mine a whole growing season or two ago. Life-cycle-wise, African blue basil (Ocimum kilimandscharicum × basilicum) takes after its perennial parent. In its East African home climate, O. kilimandscharicum doesn’t die after flowering and setting seed. (Never mind that the hybrid child is sterile. That tiny detail is beside the point.) It grows on.

I use the term tender perennial where applicable because I rise to the challenge of keeping “annuals” alive inside over the winter and replanting them summer after summer. And even counting the portion of the electric bill allotted to heating my plantry, and the time I spend taking cuttings and generally fussing over their health, it’s a decent investment too.

Self-sowers add to the confusion. Plenty of botanically true annuals return year after year more reliably than some perfectly hardy perennials. Love-in-a-mist (Nigella damascena) falls into that category along with shiso (Perilla frutescens), and California poppies (Eschscholzia californica). I always think of Verbena bonariensis as an annual because in my garden it grows, flowers, sets seed, and dies. Or does it? In fact, it’s a marginally hardy perennial (to Zone 7) and sometimes only dies back to the ground after frost, coming up fresh as a ... well, not a daisy exactly, but as itself all over again the following summer. And whenever winter kills them, seedlings will pop up in the same spots and everywhere else besides.

I know another gardener who would give perennials that aren’t great at spreading from the roots, such as coneflower (Echinacea sp.), sea holly (Eryngium sp.) and heuchera, the qualifier “short-lived.” We might think twice about purchasing a plant with only three or so years to live. Then again, in general, only the sterile hybrid cultivars will poop out completely and need to be replaced (or not); given the chance, straight species self-sow their own succession.

When it comes to buying plants, most of us gardeners simply want to know exactly what to expect. But a lot of factors are involved in ultimate plant happiness and longevity; a certain amount of unpredictability is part of the challenge. If we didn’t enjoy that we wouldn’t bother bothering. I will always be happy to shell out for one-summer wonders because my garden wouldn’t be half as lively without annuals. And with any luck some might just turn out to be perennial.

Kristin Green is the horticulturist at Mount Hope Farm and author of 'Plantiful: Start Small, Grow Big with 150 Plants that Spread, Self-Sow, and Overwinter'. Follow her blog at trenchmanicure.com.