Another look at invasive plants

Canna musafolia showing a large number of seed pods. Photo by Kit Flynn.


By Kit Flynn

Recently, my mind has been dwelling on the subject of invasive plants. No, I’m not cultivating English ivy or kudzu. Rather, this is a complicated subject simply because what might seem invasive to me in my garden may be an object of pleasure to others.

A neighbor commented that because her mahonia produced so many seedlings, she felt her gardening was limited to cleaning up after it – after all, there are only so many mahonia plants a garden can support. Because I haven’t had a mahonia for years, I could neither agree nor disagree with her sentiment although it caused me to go off on a tangent on potentially invasive plants in my mind.

Now there are certain plants, such as Japanese stilt grass, Microstegium vimineum, and kudzu, Pueraria lobata, that we all agree are dangerously invasive. Rosa multiflora also falls into this category as do Japanese honeysuckle and Japanese wisteria. Some of these were planted on purpose while others wended their way to our shores on packaging in shipping cartons. Needless to say, no one would purposely plant these plants that are listed on the official invasive lists.

However, there are also plants that have become invasive in my mind. Offer me a canna and I will probably say, “No thanks” because the two cannas I have verge on invasiveness. One is incredibly beautiful, creeping along on its rhizomes, colliding with other plants, while lovingly spewing out its seeds throughout the garden. While the seed heads are lovely, I cannot permit them to remain on the mother plant. The only thing that makes cannas tolerable in my mind is that they are easy to pull out.

The other canna, Canna musifolia, started on purpose in my side garden during a period when in my mind no leaf could be too large. Gradually, that canna overstayed its welcome so I ripped it out – but not before it had sent its seeds wafting through the air, only to settle in the far back of the garden. Today, that backyard clump is massive, expressing its desire to populate the whole area.

I’m now looking at my gladioli with a jaundiced eye. Ten years ago, a snobbish friend indicated to me that no one planted gladioli in their gardens, an attitude that immediately caused me to place an order with Brent and Becky’s Bulbs for some glads. I was careful both to choose a color I could live with and ones that were relatively short as gladioli have been known to perform an unattractive slump.

The gladioli experiment was moderately successful until the first hard rain when they then decided either to flop or to bend in half. I didn’t think much about it as I’d only planted six bulbs. Six measly bulbs in my garden do not amount to much.

This summer has seen a profusion of gladioli, arriving in garish colors, colors that I never would have chosen. One is growing on top of a small rose, absolutely dwarfing it. Others have decided to mix among the Crocosmia ‘Lucifer’ while others have chosen to become orange in color. Let me add that orange is a color I rarely use in the garden.

All this leaves me with the ridiculous question, are gladioli invasive? As far as I can determine, no one has ever accused this genus of overpopulation.

Around the same time I was going through my gladiolus conversion, I purchased Aster ageratoides ‘Ezo Murasaki’ from Plant Delights as I had some ground to cover and I wanted a fall blooming perennial. Warned that this was not a plant suitable for a small garden, I muttered that mine was a decent size garden and planted it, along with some daylilies. The aster behaved itself for five years, acting like a nice, tidy member of the community – until it decided to expand. First it traveled under the fence, which was fine with me because deer left it alone and it made an attractive border along the road.

Then it turned its interest to where the daylilies resided and cruised to visit them. The daylilies were no match for these aster stolons and today the aster fills a solid patch 10 feet by 10 feet.

There are no seeds, this plant simply has the urge to travel. Is it invasive? Can a plant be unruly but noninvasive? This is a question all gardeners have to settle in their minds because everyone runs across rowdy plants.

My answer is that the gladioli are not invasive because I can pull them out easily. The aster is not invasive because I didn’t consider its requirements when I planted it – and the plant was merely doing what its species had always done: expand to a certain width and length. The cannas are verging on invasiveness except I can pull them out easily – rhizomes remain close to the soil’s surface – but they are a nuisance in that I have to keep my eye on them throughout the growing season.

Invasive plants to me are incredibly seedy, usually hard to pull out, with so many seed heads that it’s impossible to keep up with them. That is why I deem the original Helleborus x hybridus to be invasive – and I applaud the attempts of present-day hybridizers to bring the seediness down to reasonable levels.

The point I’m trying to make is that there is a category of plants that may be invasive in my mind but are tolerated by other gardeners. We all have to make up our minds about different species that like our gardens too much. What is intolerable to you but tolerable to me is part of gardening. My advice is this: Just know your own mind and stick with it.

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