In last weekend’s Sunday Star Times, I shared my (not particularly scientific) theory that sowing sweet peas around swan plants can work to deter wasps. Here’s the column:

Metamorphosis. It’s the longest word in my three-year-old son’s vocabulary, though it’s only a matter of time – thanks to a muster of monarchs – before he masters the pronunciation of prestidigitation.

Egg, caterpillar, chrysalis, butterfly: it’s an enchanting cycle of everyday magic, conjured up in your own backyard for the price of a swan plant. A cheap trick, but one no less satisfying however many summers you’ve seen it.

Wisdom, said Socrates, begins in wonder. Be curious, said Stephen Hawking. Watch out for wasps, I say to my kids, for nothing deflates childhood delight quite like the sight of German yellowjackets gorging barbarically on monarch butterfly caterpillars, mining their chubby carcasses for protein.

As an organic gardener, I’m loath to intervene in the natural order of things. But unlike those wildlife photographers who stand by, cameras rolling, as bewildered baby wildebeest are ripped to bits by lions, I also can’t bear to witness the carnage. So last spring, when I planted my swan plants – 16 milky-sapped clumps ofGomphocarpus physocarpus in a four-square-metre bed – I sowed scented sweet peas around the perimeter at the same time.

To be honest, I wasn’t thinking about wasps the first time I paired these two plants. I was simply trying to hide the plainness of the swan plants. For the first half of the season, before the butterflies descend, these boring green bushes are bereft of any notable beauty. Their itty-bitty white flowers are as elegant as phalaenopsis orchids, but they’re too damn small to add any real decorative appeal, which only leaves the puffy seed pods as a point of difference.

Some gardeners compare swan plant seed pods to balloons and cotton balls, but their common name comes from the flocculent, swan-like wings the ripe pods produce when they split open. Truth be told, I’ve always found swan plant seed pods rather more testicular in appearance. If only the English common name of bishop’s balls had caught on here.

To recap: ordinary foliage, insignificant flowers, pubic pods. And that’s even before you factor in how gruesome swan plants look once they’ve been chewed bare by very hungry caterpillars in late summer. So I figured, why not plant them behind a barrier of something pretty like sweet peas instead? I had a hunch that it might look nice, and it did, as by late summer my sweet pea vines sport scores green and gold chrysalises, like rows of greenstone pendants in a souvenir store.

(If you’ve ever wondered why monarch caterpillars spin their chrysalises under your house eaves, along villa weatherboards or indeed anywhere other than on the swan plants they were raised on, it’s because their manners preclude them from falling asleep on their friends’ dinner plates.)

But the real beauty of this experiment? The wasps now leave them well alone. Was the sumptuous scent of all those old-fashioned sweet pea petals simply overpowering, like the original Poison perfume, or had I inadvertently stumbled upon a completely non-scientific, but nonetheless surprisingly effective, natural wasp deterrent?

To test my theory, I phoned Dr Keith Hammett, QSM, BSc (Hons), PhD, president of the Royal New Zealand Insitute of Horticulture and the southern hemisphere’s preeminent sweet pea breeder. “Have you ever,” I quizzed him, “seen a wasp sitting on a sweet pea?”

There was silence at the other end of the line. I suspect he thought it was a trick question.

“No,” he said, adding, because he’s a smart marketer as well as a brilliant plant breeder, that now’s the perfect time to sow seeds of his lovely ‘Solstice’ series of winter-flowering sweet peas, which you can order direct from www.drkeithhammett.co.nz.

Update: My sweet pea vines finished flowering this week, and what did I find this morning? About half a dozen formerly chubby but now parasitised monarch caterpillars, their striped pyjamas hanging forlornly on the plants. Gawd, it’s such a depressing sight.