Don’t Try This at Home

by Henry Homeyer

CORNISH FLAT, N.H. – Over the years I have come to realize that not every pretty flower deserves a place in my garden. Some bring more trouble and aggravation than they are worth and require constant vigilance to keep them from completely taking over the garden. As I look back over the mistakes I have made in the garden, I can think of several plants that I wish I had never planted, or that I had planted differently. This column can be thought of as your “Do Not Try This at Home” warning. Come spring someone may offer you a nice division of one of these plants. Don’t say you weren’t warned! One fall I cleaned up an asparagus bed that had been performing poorly for quite some time. It had been overtaken by weeds and an aggressive perennial known as Queen of the Prairie (Filipendula rubra). I spent hours combing through the soil and removing everything in the bed. Come spring I will plant lettuces and other annual vegetables in that bed, all the while keeping my eyes open for a reappearance of that sneaky Queen of the Prairie.

The Queen, as I think of her, grows to be six feet or more tall and has masses of pinky plumes slightly reminiscent of astilbe flowers. It’s lovely. So what’s not to like? The roots can grow three to four feet long, branching and sending up new plants at each root node. When I planted it near the asparagus patch I wasn’t worried, as the asparagus was growing in a wood-sided raised bed with eight-inch sides. It never occurred to me that its roots would sneak under the boards, pop up in the asparagus patch, and take it over. Silly me.

Then there is the Japanese butterbur (Petasites japonicus). It’s an interesting plant with huge leaves – some are almost two feet in diameter on long stems that rise from the ground and reach three to four feet in height. Early in the spring funny flowers on pinky stems appear before the leaves, popping up everywhere like drumsticks.

I did a better job of situating it than I did with the Queen of the Prairie. I knew it spread by root and liked moisture, so I planted a small clump near my stream. It is contained by the stream on one side, and my lawn on the other. No problem, I thought. But, once established, it can send new shoots up several feet from the mother plant. It has spread along my stream and, although handsome, I see no way to prevent it from marching, like General Sherman, all the way to the sea.

Goutweed, however, is the most persistent of all plants I have encountered. It is a groundcover that was introduced because it will grow in wet or dry soil in sun or shade. And you can’t kill it. It spreads by root, and even one scrap will start a new colony.

I got a few scraps of goutweed root along with some iris given to me by a friend many years ago. It took over the iris, despite persistent weeding. Finally, I dug up the patch and lugged away all the roots and soil to a depth of a foot. I dumped the soil and roots at a far corner of my property wrapped in black plastic, much as one might do with toxic waste. I put down landscape fabric and anchored the perimeter with large stones. Then I refilled the space with new soil that I purchased. Five years later a scrap of goutweed snuck out from under the barrier and poked its head up. Five years with no photosynthesis, and it was still vigorous!

So what can you do if you want to grow a plant that can be invasive? First, be very careful. Don’t plant it first and ask questions later. Read up on it, and talk to good gardeners with experience. Queen of the Prairie is much less aggressive in dry soils than in moist soils, for example.

There are barriers you can use to contain aggressive plants that spread by root. In warmer climates than ours bamboo can be gorgeous and will take over. I got some hardy bamboo years ago and, knowing it could be invasive, buried a 55-gallon plastic drum to grow mine in. That was overkill, as our climate is such that I had a hard time keeping it alive over the winters and eventually pulled up the struggling plants.

I learned at the time that polyethylene barriers for bamboo are available. It comes in 36-inch wide rolls of 40-mil plastic. For full containment needs to be installed so that there is a three-inch lip above ground and the edges must be overlapped by six inches and sealed so that no roots can squeeze out between the overlapping layers. You have to really, really, want to grow Japanese butterbur or Queen of the Prairie to go that extreme. But there are those of us who will try almost anything, once.

So as you sit in your cozy chair dreaming of spring and all the wonderful gardening projects you will do, dream realistically. Do your homework before you decide what you will add to the garden. I wish I had.

[Homeyer wrote this article in 2010. He is writing new articles just once a month this winter. You may reach him at [email protected].]