Kudzu Could Become Invasive in Southern Ontario
Answered by: Conrad Richter
Question from: Jane Murphy
Posted on: January 21, 2008

I was distressed to see that kudzu seeds are for sale in your latest catalogue. I’m sure you’re aware of the ecological damage that the plant has already caused in the U.S. southeastern states. However, are you aware that it is now found in New York State, according to the USDA species map? [see USDA/plants, search Kudzu and scroll down to distribution map.] It appears that it is present in Connecticut as well, and in Oregon. With climate change, it is entirely possible that it could survive winters in southern Ontario. Please do not sell the seeds. Once the damage is done it can’t be undone.

You raise a very difficult question. Many of the herbs in our catalogue are weeds somewhere in the world, and some are weeds in Canada and U.S. So too are many of world’s important economic and horticultural plants -- a cursory look at WeedsUS database (http://www.nps.gov/plants/ALIEN/list/WeedUS.xls) reveals many of these, including hollyhock, celery, asparagus, wormwood, St. John’s wort, and many more. In the herb industry, St. John’s wort, dandelion, and burdock are some of the most important medicinal herb crops; yet these are considered noxious weeds in some jurisdictions. Do we ban them all?

Richters has taken a responsible approach to the sale and distribution of invasive plants. We do not sold kudzu seeds to the U.S. even though the USDA has never banned the importation of kudzu seeds into the U.S. We felt that it was the responsible thing to do, despite many inquiries (and even upset customers) from the U.S. And the Richters catalogue denotes which provinces and states we will not ship certain plants and seeds where there is a risk of damage to the local ecosystem. We even have some herbs we do not ship to our Canadian customers because we feel that they are important medicinal plants and that they should remain available to people in other parts of the world where the same plants are not invasive. In all, our 2008 catalogue has 24 items that cannot be shipped to a province or state in North America.

In order for a plant to be invasive, it needs to be be able to propagate itself, either sexually or asexually. Winter survival in itself does not mean that a plant will become invasive. For example, if a plant fails to reach the flowering and fruiting stages before the frosts arrive then it can’t produce seeds and can’t spread. Even if a plant can survive the winter and reaches maturity and produces offspring, that still does not mean it will be invasive, for many reasons, including the probability that it can’t compete well against other plants better adapted to the local conditions. And even among invasive plants, there are many that we find that we can manage quite well such as dandelion and burdock. So there is more than one hurdle before a plant becomes a threat to any ecosystem.

What we know about kudzu in Canada is this: in over 20 years of selling it here there has been no evidence that it is able to survive our winters. It can only be grown as a summer annual just like tomatoes, peppers, and geraniums -- all perennials in warmer areas. Kudzu is not even past the first hurdle towards becoming invasive in Canada.

But you quite rightly raise the spectre of climatic change and how that is creating new challenges to ecosystems. We must think how that may affect the future invasiveness of plants. It is a fair question to ask whether kudzu should be removed from our catalogue as a proactive move. However, at this time, weighing all the evidence, we do not feel that the plant is a risk in Canada. We are, however, watching the results of a University of Toronto study underway to determine the plant’s potential to become invasive. If the results of that study show that the plant does present a risk, then we will restrict sales or remove the item from our catalogue accordingly.

You may be interested in reading Stephen Strauss’s article on the demonization of kudzu:


This article speaks much about about our worry that we may be demonizing certain plants unfairly. We have seen waves of this sort of thing over the years (purple loosestrife is a notable example -- it now appears to be receding in Ontario). It seems to us that there is a need to take a more balanced approach before we ban useful and interesting plants altogether.

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