In my early days of gardening, I made a few mistakes. Most were fairly minor and rectifiable, but there were one or two where I lived with the unfortunate results for a very long time. I'm talking about invasive plants – the sort that beginning gardeners, especially, are inclined to make a bee-line for because they usually come with the exciting tag: "easy to grow".
Jerusalem artichokes still strike terror into my heart. We planted ours in an area of sandy, well drained soil in which they thrived. It was only after growing them for a couple of years that we admitted to ourselves that we weren't actually too partial to them. By that time, they were making a determined bid to take over the entire section. We tried digging out every last one – and failed. We dug again the next year, and even sieved the soil to collect what we thought were the last of the tubers – no such luck. In the end, with the help of a wonderful team of WWOOFers, we smothered the emerging plants with black plastic and, by piercing small holes in it, planted a small forest of fast-growing native trees through the slits. Success at last, and exhaustion.
Then there was the horseradish. Have you any idea how difficult it is to rid it from your garden? With a taproot that reaches almost to the centre of the earth, it is impossible to dig out, snapping off at the slightest touch and regrowing from the tiniest fragment. I have never before been reduced to putting spray anywhere near my vegetable garden, but horseradish drove me to it. I carefully painted each leaf with Roundup, then left the bed fallow for a year.
Tansy? Never again! It's reputed sandfly and mosquito repelling properties never did materialise but while we were awaiting them , it spread at a rate of knots through every inch of the herb garden, smothering everything else in its path (except for the comfrey, but that is another story). Ditto for apple mint (which was a rival even for the tansy), and hot on its heels came Vietnamese mint. It looked so innocuous in its pot until, one day, I discovered its roots had broken open its plastic container and it was taking over the glasshouse (and that was in the depths of winter – at the bottom of the South Island!).
I don't even want to talk about the miner's lettuce – or the celery parsley that self-seeded all over my paths, but I do want to say that there are ways to enjoy these invasive little monsters without them taking over your precious garden beds. I currently have a healthy crop of garden mint (the fragrant mint-sauce type) growing just below the garden tap where it enjoys moisture from the occasional drip or overflowing bucket. But, because I know just how quickly it can take over the garden, it is growing beside a concrete path on the far side of the built-up beds, and is well contained by a ring of corrugated iron sunk deep into the ground. The tayberry (a monster if ever there was one) has not only a third of its branches removed each season but, in order to contain it, also its roots. The sorrel grows in a deep plastic container under which I have placed a wad of weed matting (checked regularly to make sure no roots are tunnelling through). I also cut down its seed heads as soon as I spot them. My celery-parsley, which I wouldn't be without for winter soups and stews, now grows in a polystyrene box on the deck where, should it seed without my noticing, there is noting for the seed to grow in.
Just because a plant is invasive, there is no reason why it cannot be enjoyed providing we take adequate precaution to isolate it. Even if, in the case of my comfrey, it means banishing it to a far-off paddock!