Question: A few years ago, a friend gave me a start of mint, which I planted in my garden. I love it, but it’s formed a patch several feet wide and is now crowding out the other herbs. How can I get rid of it? I don’t want to use an herbicide.
Answer: Now that you’ve seen how vigorously mint grows, maybe you could move some to a place where you won’t care if it spreads, or try confining it to a half-barrel planter or other large container. Meanwhile, there are two good ways to regain control of your garden without using weed killer. You can dig up the mint or smother it.
First, secure the perimeter
If you haven’t examined the mint patch since last summer, you’re in for a surprise. At the end of the growing season, mint spreads out a network of rhizomes, stems that grow horizontally at or just under the surface of the soil. They lie in wait all winter, then sprout up fast in spring.
Rake away any mulch or debris from around the edge of the patch and look for new shoots. If you don’t find any, explore the top few inches of soil for rhizomes. They’ll smell minty and be about as thick as cooked spaghetti, with tufts of slender white roots every inch or so. Buried rhizomes are white, but those growing on the surface turn green, purplish, or reddish.
When you’ve determined the outline of the mint patch, dig up any other plants that are growing within the area as you won’t be able to work around them. Shake the soil off their roots and pick out every bit of mint rhizome before you transplant or give away these plants; otherwise, the mint will travel along with them.
Dig it out
Dig the patch of mint when the soil is evenly moist, not muddy-wet or dusty-dry. You need to dig through the entire area systematically: For example, you could start at the front edge and work back and forth in strips about a foot wide. Be careful not to step or pile soil onto any place where you haven’t dug yet.
Use a digging fork. Stick the tips of the tines into the soil, then lift forward and up to “comb” out the mint rhizomes. They don’t grow very deep, and they’re easy to see. Peel them up in long sections and toss them into a trash bucket. Pick up any short pieces that break off. A lot of breakage probably means that the soil is too wet. Stop, wait until it gets drier, and try again.
Some gardeners go so far as to sift the soil through a big sieve made of 1/4-inch hardware cloth to remove every bit of rhizome, but I don’t think it’s necessary. Instead, let the bed lie undisturbed for a month or so and pull out any mint sprouts as soon as you spot them.
When the area seems mint-free or nearly so, you can prepare the soil and replant the bed. Be vigilant for the rest of the growing season, though. Keep watching for and removing sprouts because, as you well know, it takes only one start to form a patch.
Smothering is easier than digging but takes more patience. Rescue any other plants from the area in early spring, but let the mint get at least a few inches tall. Then cut it right down to the ground. Immediately cover the whole area with sections of folded newspaper at least four pages thick; avoid using pages printed with color. Overlap the sections like shingles, leaving no gaps. Extend this covering about a foot beyond the apparent edge of the patch, then hide and anchor it with a layer of your favorite organic mulch.
By blocking out the light, this covering of paper and mulch will weaken and kill a patch of mint or any other perennial you want to eradicate, but the process takes a full growing season. If you don’t want to look at a patch of bare mulch all summer, set some big containers of colorful herbs there or plant a hill of pumpkins or gourds at one side and let the vines scramble over the mulch. By late autumn or the following spring, the mint will be dead, and the mulch and newspaper will have decomposed. Then you can prepare the soil as usual and replant the bed with new plants.
Rita Buchanan grows many herbs in her garden in Winsted, Connecticut.