The lingering warm weather earlier this month had brought the garlic mustards back to life and I was happy for the opportunity to get ahead of what is usually one of my first spring chores: pulling them out with that long white taproot intact. I have been pulling garlic mustard for almost 10 years and have observed, over a 15-acre swath of land, not only a decline in the quantity that grows (and is therefore removed), but also a regeneration of native plants in that space.
I took a break recently to watch the Connecticut Invasive Plant Working Group Symposium. It rather turned my world upside down.
The keynote speaker, Bernd Blossey of Cornell University, delivered a bombshell recommendation in his talk “Invasive Plant Management”: that, aside from a stray here and there, it would be better to not to pull garlic mustard at all. His research shows that garlic mustard left alone will, over time, decline in numbers and in plant vigor. This, he posits, is due to negative soil feedback, which is what happens when plants are grown in the same soil year over year. It is the reason why crops are rotated.
I really wanted to pretend that I had never heard this, but my conscience wouldn’t let me. I have made a concerted effort in writing this column to seek out the science behind what I observe in the woods with respect to native and non-native species. And it is difficult to get definitive answers, perhaps because of the variability in environmental conditions and the fact that outcomes are difficult (though not impossible) to measure, especially over long periods of time. There are differences of opinions among experts on best approaches to invasive management.
Doing nothing is always tempting advice. Sadly for my back, I am not sufficiently patient to wait the 10-20 years that Blassey says it takes for the negative soil feedback effect to work on garlic mustard. And there will always be garlic mustard around, as seeds will be spread by animals. In fact, Blassey’s No. 1 recommendation to stop the spread of invasive plants, and to encourage native plant spread, is to install deer fences — simply not practical in my case.
I went back to rewatch the presentation, and listened to the audience questions at the end. And here is where things came into focus: Blassey conceded that his laissez-faire approach to garlic mustard may not be relevant for what he calls the “woodland gardener” but is geared to nature preserves and land trusts.
And so I would adapt his prescription as follows:
— Garlic mustard populations can be reduced but never be fully eradicated unless the area is fenced to keep out deer.
— If you have a large area of garlic mustard and want to try Blassey’s approach, make an effort to fence the area. If it cannot be fenced, you may want to mark the area with flags so you can monitor the size of the area year over year. You should see the garlic mustard lose vigor in the center as it spreads out beyond the initial area.
— Don’t assume that this prescription will work for other species.
— The best method of control is to not allow garlic mustard to proliferate in the first place. This is where pulling it out is most useful. Be sure to pull it before it goes to seed. A hori hori knife or other weeding implement might be helpful to loosen the taproot from the soil so it comes out in one piece and does not disturb the soil too much.
— If you do weed garlic mustard, be thorough in that area and visiting several times, starting from when the ground unfreezes in spring to when it freezes again in winter. The key to success is doing one’s best to halt new seeds from spreading.
— Plant native plants in the woods and tend to them, fencing them if necessary to protect them from deer browse.
Dee Salomon “ungardens” in Litchfield County.
