Plants behaving badly
Senior horticulture editor Stephen Westcott-gratton declares a pox on willful botanical invaders.
I probably should have written this column a year ago, but to be honest, when I first heard about the recent proliferation and spread of wild parsnip (Pastinaca sativa), I pretty much dismissed it as just another weed du jour. After 25 years of gardening, I’ve seen several epidemics come and go: First there was purple loosestrife (Lythrum salicaria), which threatened to carpet the country and crowd out native species with its pretty purple flowers. Although it’s still a menace in some areas, the deliberate introduction of two European leaf-eating beetles has done a great deal to restrict its range. Nevertheless, gardeners should never plant purple loosestrife in their borders, including the supposedly sterile cultivars that still occasionally show up at local plant swaps. The next invasive species I recall causing a media frenzy wasn’t a plant, it was a bug: magnolia scale (Neolecanium cornuparvum). I remember doing a segment about it on Citytv’s Breakfast Television about 20 years ago and watching the host recoil from the infested branch I brandished at the cameras. Super-yucky magnolia scale was a serious problem for several years, but as is often the case, nature restored a balance, and now it’s just another gardenvariety insect pest (you can knock adults off branches with a strong jet of water, and autumn applications of dormant oil will kill any overwintering nymphs). Where I live, the last furor was over giant hogweed (Heracleum mantegazzianum), and I was both amazed and delighted to see how quickly local municipalities jumped all over this floral thug. Giant hogweed – along with parsley and carrots – is closely related to our most recent plant plague, the wild parsnip. A few months ago, I had cause to take wild parsnip seriously when I saw what it did to a neighbour’s teenaged son; in short, it made the worst poison ivy look like a day at the beach. As with giant hogweed, the above ground parts of the plant contain a sap that reacts with outdoor UV rays to cause severe burns, blisters and scars – if it gets in your eyes, permanent blindness can result. Surprisingly, “wild” strains belong to the same species as our cultivated vegetable types (delicious ‘Albion’ and ‘Gladiator’, for example), so it’s possible that they’re just agricultural escapees that have reverted to their undomesticated form. Nevertheless, parsnips have been grown in North America for more than 200 years, so it’s a mystery why they’ve gone rogue so swiftly. Wild parsnips have been reported in every province and territory except Nunavut. Small infestations (less than 100 plants) can be dug up in spring, but you’ll need goggles, heavy rubber boots and gloves and haz-mat-style coveralls. It’s the sort of job that’s generally best left to professionals. But despite the bad behaviour of the wild parsnip, I’ll still be eating my share of sweet roast parsnips with Sunday dinner.
Wild parsnips are biennial, so preventing second year flowers from setting seed is an important control strategy. Left alone, the plant can form large colonies, crowding out native species and seriously reducing biodiversity.
Wild parsnips are a reminder that kids must never pick or eat any plant Without adult supervision.” stephen Westcott-gratton, CG senior horticulture editor