When we think of invasive plants, we often imagine the common reed or the Japanese knotweed, crossing the oceans aboard a large cargo ship. We think of these transport pallets which possibly imported the first root fragments of these ugly plants which have invaded our landscapes. Ah, the evil freight industry! Unfortunately, sometimes we have to take a step back to contemplate… ourselves! Yes, gardeners and horticulturists also bear the burden of a few introductions of invasive plants. And the giant butterbur (Petasites japonicus subsp. giganteus) even if it is “sooo beautiful at the edge of the woods” is one of those plants that we should learn to do without.
A Bit of Info on This Big Invader
The giant butterbur is a plant native to Japan, Korea and a few islands in eastern Russia. It is a perennial that rises from the ground each spring, first emitting a stiff stem topped with more or less attractive pale-yellow flowers. Then the leaves appear, which can measure up to three feet (one meter) in width. I will admit, that’s pretty darn awesome! The plant likes slightly moist soil and cool undergrowth. It is therefore an ideal plant to give a touch of wow! in the shade garden. And this is the main reason behind its popularity among avid gardeners. All in all, it’s a pretty spectacular plant, you have to admit, and it’s also one of the star plants of the famous ravine in the Jardins de Quatre-Vents. It is also highlighted in many sumptuous private gardens in North America.
It is believed that this Asian plant entered North America via British Columbia. Then it slowly made its way east. In Quebec, it was found present in natural environments in 2007. This makes it a fairly recent introduction, compared to several other invasive exotic plants.
So far, nothing too alarming, on the contrary. But… it gets complicated, partly thanks to its vegetative mode of reproduction. This means that the plant multiplies by underground rhizomes which slowly but surely colonize its surroundings. Thus, the colony grows a few feet each year. Moreover, the plant is dioecious, which means that it rarely multiplies by seed, because in general, all the plants in the colony are of the same sex. Then, add to that the fact that it is not so easy to dislodge. It’s one of those plants that no matter how hard you dig up, collect as many roots as possible, there’s always a little forgotten piece that comes back. Think of the pleasure one can have in trying to eliminate gout weed (Aegopodium podagraria) or the Canada anemone (Anemonastrum canadense).
What Exactly Is an Invasive Alien Plant?
According to the Program for the battle against invasive exotic plants, it’s a plant “introduced outside its natural range, having the ability to establish and reproduce successfully and whose spread may have significant environmental, economic and social consequences.” There is a fascinating side to these plants from elsewhere! They are able to adapt to their new homeland… a little too much to the taste of other plants in the natural environment. Butterbur grows naturally in moist soils and it is not surprising that it feels a little too much at home on the edge of streams in a forest environment.
In the case that interests me here, that of the giant butterbur, the real concern is that where the butterbur settles, nothing else grows. And this is one of the characteristics of invasive alien plants: they represent a threat to the biodiversity of the natural environment. All the soil under the broad leaves is completely deprived of light. Native plants disappear as the giant butterbur spreads. No more ferns, no more trilliums, no more lycopods, little violets and Carolina Claytonia … ah! Claytonia! It is therefore without doubt that I affirm that butterbur is a plant harmful to other species.
Currently, in Quebec, there are 18 species that are designated as priority invasive alien plant species (in French only). This means that these are plants that are monitored very, very closely, in terms of prevention, detection, monitoring and control. On this list of the worst of the worst, we recognize, of course, the common reed (Phragmites australis) and the Japanese knotweed (Reynoutria japonica, syn.: Polygonum japonicum). Surprisingly, the Norway maple (Acer platanoides) is also found there. These misfits are recognized for their negative impacts on the environment and sometimes even on the economy. They can pose a threat to the disappearance of native species. Their management and control can generate astronomical costs. In some cases, their presence can even lower the value of a property or land.
Of course, one of the first recommendations concerning these green devils is not to cultivate them… on a voluntary basis! Even if in the sense of the law, there are very few plants whose production and sale are prohibited, isn’t it obvious!
When we compare the behavior of the Japanese butterbur in the natural environment with the definition of invasive alien plants, we can only come to a somewhat worrying conclusion. Yes, it’s only my personal experience speaking here. I see this plant more and more often in gardens and I also see it colonizing more and more natural undergrowth in the backyards of these beautiful gardens which have the forest as a backdrop. And that worries me. We saw the giant hogweed being at first a collector’s item and then becoming the plant to destroy, we can only foresee a fate similar for the giant butterbur. Maybe I’m a little Nostradamus in the making? Maybe my observations are not representative of reality? But I don’t think we’re too far from a future announced disaster! And I’m not the only garden specialist who thinks this plant is a monster!
So, my advice is the following: Let’s not wait to find ourselves with another horticultural misstep and start now the eradication of the few colonies on their way to conquering the universe. If we had detected the common reed or the Japanese knotweed as soon as it arrived, we wouldn’t be worrying about it today.
Is not invasive who wants!
There is a certain kind of privilege to be given the status of invasive alien plants. In fact, not all plants introduced into North America are eligible for this special mention. Let’s not forget that dandelions, daisies and wild chicory are also introduced plants, but they have managed to integrate into the landscape, to cohabit with native plants, which means that their presence goes almost unnoticed. It is estimated that about 10% of introduced species turn out to be real invasive alien plants.