Recently I purchase one of the well-known resource books on landscape plants. That same week I received in the mail a folder listing invasive plants in Pennsylvania. Many of the plants denounced in the folder were praised in the resource book. Nursery and seed catalogs list some of them and garden centers stock them. I have planted a few of them in my own landscape and others have invaded on their own initiative.

It is easy to understand why these plants are sold. They are easy to propagate and are therefore profitable. Some were originally promoted by the U.S. Department of Agriculture as solutions to problems. Multiflora rose and kudzu come quickly to mind.

I helped plant what seemed like miles of multiflora rose hedge rows when I was much younger. Hedge rows were an affordable luxury then and provided food and cover for wildlife. It wasn't long, however, before the multiflora rose left the hedge rows and formed impenetrable thickets in the meadows.

Some of these invasive plants appear to be well-behaved in our landscape. The problem behavior occurs out of our sight as birds carry seeds that germinate elsewhere. Others have no redeeming features and do not find a welcome anywhere. Two examples are mile-a-minute vine (Polygonum perfoliatum) and Canada thistle (Cirsium arvense). You won't find these plants for sale anywhere.

The Japanese barberry (Berberis thunbergii) is on the Pennsylvania list of invasive plants. The barberry is widely available and is enthusiastically promoted as a landscape shrub. I have never seen it in the wild, but seedlings appear often in the shrub borders. I would feel as sense of loss if I removed it from the borders.
I would feel triumphant if I could eliminate crown vetch (Coronilla varia) from the landscape. It is unwanted, unloved and thriving. Just a moments inattention and it appears in another part of the garden. The chances of eliminating it are small because it covers acres of road side banks; planted there to prevent erosion.

Some of the plants on the list were a surprise. After trying unsuccessfully to grow watercress (Nasturtium officinale) in a spring drain for years I find it is an invasive plant in Pennsylvania.

A complete list of the invasive plants in Pennsylvania is available from the Department of Conservation and Natural Resources, Bureau of Forestry, FAS, P.O. Box 8552, Harrisburg, PA 17105-8552