Hello,
The homeowners before us planted mint in the backyard, right in the ground, no pots.
It’s spread all over our yard – what’s the best way to get rid of it organically (no herbicides, we have small children)?
Thank you!
While killing plants is something we try hard to avoid, sometimes it is necessary. As much as I love mint for its many culinary uses, there are several varieties in Canada that can become highly invasive if planted directly into the garden without barriers.
As you have probably noticed, mint spreads by sending out rhizomes- which are underground stems. Manually removing the plants in the spring while the ground is moist, can significantly reduce your overall mint population.
Care must be taken to remove the rhizomes along with the parent plant. If the rhizome snaps, any remaining pieces have the potential to start a new plant.
If you have a small garden, and work methodically, you will get on top of it. It may take repeated spring and fall weeding to get all of it, but the number of plants will diminish each year.
If you have a large garden with an extensive mint invasion, then covering the mint may be a better option. Smothering, also known as ‘sheet mulching’, the mint with cardboard or layers of newspaper will deprive it of water and sunlight.
Most mint varieties enjoy moisture and a minimum of 4-6 hours of sunlight. Without sunlight the mint won’t be able to photosynthesize and will die.
If your mint infested area has other plants growing in it, I would recommend hand weeding the mint away from the other plants about a foot, then proceed as follows:
Cut the mint down close to ground level. If you use a lawn mover, attach the grass catcher- to prevent small stem pieces from landing elsewhere and sprouting.
Cover the mint infested area with flattened cardboard. Multiple layers of wet newspaper can also work. You can put some rocks on top to weigh it down, to stop it blowing away. A more attractive option is to cover your cardboard/newspaper with 2-3 inches of garden mulch- being careful to avoid the stems or trunks of any existing non mint plants by a few inches.
This can take 4-6 weeks to see results. The dead mint will breakdown with the cardboard/ newspaper if you leave it in place. You may need to repeat this process again next year if any residual mint re-sprouts next spring. The second year crop is usually much more manageable and can be hand weeded so that you can get on with designing and planting out your new garden.
You may have also come across the term ‘solarization’. This can work quite well if your problem area is in full sun. The downside with solarization is that it requires the use of thick plastic sheeting instead of cardboard. The sun heats up the plastic and kills the plants and anything else living in the soil. Studies have found that the sun can degrade the plastic, allowing microplastics to be shed into your garden soil and the atmosphere. High quality, UV treated, new plastic sheeting is less likely to release microplastics, but should be discarded after single use.
Solarization takes about the same time as covering with cardboard, so I don’t see any advantage in that method given the negative environmental consequences.
Since you cannot plant in the cardboard sheet mulched area until you are satisfied the mint is gone, you may like to put planters, urns or pots on top of the mulched bed so you can enjoy your garden.