MYSTERY BROOM
If you are attuned to plants, you never know when you’ll encounter a plant identification mystery. My daughter and I found one last week while we were out for a walk on a local side street. We were passing a house that sat on a corner lot atop a slight embankment. The owners had planted various shrubs and perennials on the embankment, probably for erosion control as well as appearance. We both noticed a three foot tall shrub whose arching branches bore small, rosy purple flowers. The blooms looked like tiny butterflies and the total effect was airy and delicate.
“It looks like broom,” said my daughter with authority. She was right and I was pleased. She has been exposed to the fundamentals of plant identification since she was tiny, and though she disdains any mention of a horticultural career, she has acquired a lot of knowledge. Her identification was based on the overall size and shape of the plant and the configuration of the flowers as well as the appearance of the small, oval-shaped leaves characteristic of brooms and other members of the pea or legume family. We have both seen lots of yellow-flowered broom or Cytisus scoparius at various garden centers, but neither of us had ever encountered a purple-flowered specimen. “You’ll have to look it up when we get home,” she added. I had my marching orders.
The only thing that bothered me about this particular purported broom was the bloom time. Common broom, which is sometimes called “Scotch” broom, generally blooms in the spring. Blossoms in late summer didn’t seem to fit the plant profile.
For some reason I have never grown broom in my own garden. I have other yellow-flowered shrubs, like forsythia, winter-flowering jasmine and Japanese kerria, but no cheerful Cytisus scoparius. When I think about it, it’s probably because brooms, like forsythia, are really only interesting when they are in bloom. Since I am a lazy gardener with limited space, I gravitate towards plants that can provide more than just a few weeks of fleeting blossoms and a weedy growth habit.
Research confirmed the initial identification. Cytisus scoparius is available in rosy purple as well as orange and shades of the usual yellow. As for the odd bloom time, there is an easy explanation. Scotch broom blooms in the spring on old wood and can bloom again later in the season on new growth. Evidently the broom that we saw had decided on the latter course of action.
As is frequently the case with these small-scale plant mysteries, my broom research opened the door to a much larger issue. That issue was invasiveness.
Broom is native to northern and central Europe as well as the Mediterranean region. It probably arrived in this country during the late eighteenth century with the colonists, who used the stiff stalks for broom making. Allegedly, shipments of whiskey sent to the “forty-niner’s” during the California gold rush were cushioned with bundles of broom. Seeds attached to those bundles germinated, bringing broom into the western United States and Canada, where it has become a major plant pest.
Like all invasive species, broom is a victim of its own vigorous nature. States and counties have long planted it on highway embankments for erosion control because its strong roots hold the soil in place, and it spreads rapidly to cover erosion-prone areas. Unfortunately, in the West broom outcompetes just about everything else, creating a monoculture in many places. Invasive plant websites are full of information about broom eradication, which can be difficult and time consuming.
So where does this leave gardeners who might want to grow Cytisus scoparius? Nurseries, even some in western states, still sell it, though at least one warns purchasers to “remove seed heads” to curb rampant tendencies. If you live in the West, the answer is obvious–don’t buy broom unless you are absolutely positive that the species or cultivar you purchase is non-invasive. Easterners have more latitude, since climatic conditions in the East don’t seem as favorable for this attractive shrub. However, it’s still better to buy something like Burkwood’s broom, Cytisus scoparius burkwoodii, which may be the cultivar that my daughter and I saw. It’s buds open nearly red and fade to a purplish hue, and it does not have the invasive tendencies of some of its relatives.
When I first saw the mysterious broom, I had the urge to rush out and buy one for my garden. Now I think I’ll pass on this particular plant, even though the flowers are beautiful. By spurning broom I can accomplish two things–contributing to a healthier ecosystem and disproving my husband’s assertion that I buy every new plant that I see.