Peppermint, spearmint, lemon mint (lemon balm), chocolate mint, horse mint, catmint and similar kinds of mint are easy to grow and are very good aromatic additions to the garden or flowerbeds. They do have a drawback, however. Mints tend to be invasive. If steps aren’t taken to prevent it from happening, mint can take over the flowerbed or garden. These plants can be grown in pots, however there is also a way to keep it from spreading out and taking over when it is planted outside.
Perhaps no mint is better known for its propensity to spread than peppermint. However, all members of the mint family will spread if the conditions are right. Some species, such as sage, thyme, basil and anise sage spread primarily by seeding themselves. To keep these from spreading, simply remove the blossoms before the seeds have a chance to form. Peppermint, spearmint, lemon mint, catmint and others spread primarily in a different way, however. We’ll use peppermint as a representative example.
As a peppermint plant grows, it begins to put out underground rhizomes. These roots are usually one to three inches deep and run generally parallel to the surface. They can also grow over two feet in length. From the rhizome, new plants can emerge periodically and once they break the surface, they become self-sufficient plants, which can in turn produce more rhizomes. Many people with lawns are aware of this principle because this is exactly how crab-grass spreads. The rhizomes are actually a survival mechanism because as hardy as mint is, eradicating it is extremely difficult. If you try to get rid of the plant and leave just a bit of the rhizome that has a plant node on it, the mint will continue to grow. The key, then, is to prevent the rhizomes from spreading to begin with.
Blocking rhizome spread
To contain the mint, start by digging up the area you want to have the mint growing in. Remove the dirt to a depth of at least a foot. This also gives you the chance to mix finished compost in with the soil before using it again. Mint isn’t picky about having rich soil and will grow in quite poor soil, but if compost is mixed in, you should be able to have a sustainable mint crop for years.
Once the dirt is removed, line the hole with two layers of black plastic, making sure that it is weighted down. Put the dirt back into the place the mint is going to be planted, then plant the mint a few inches apart and water the mint well. It might not seem like there isn’t much mint there at first, but it shouldn’t take long for it to fill out the patch. A patch that is two feet wide and four feet long is likely to produce all the mint the average family is likely to use.
How it works
How the black plastic prevents the spread of the mint is simple. The plastic prevents the rhizomes from going beyond the sides of the patch, forcing them to turn inward. This helps the plants to fill out the mint patch rapidly, while slowing down the invasive nature of the mint. This isn’t a long term solution, because the black plastic will eventually decay, allowing the rhizomes through. It might sound like a lot of effort for something that is only going to work for a year or two, but really it isn’t. If the roots are permanently contained, within a couple of years the plants can become root-bound and the growth will become stunted. The plants can even die. This happens in pots, too. This means that every couple of years (more often with pots), the mint should be dug up, separated and replanted. That is the perfect time to replace the black plastic. It is also a great time to make sure that there are no persistent weeds and grass growing in the mint patch.
By using the black plastic, the mint can be prevented from spreading and being invasive. By maintaining the patch and doing the separating and replanting every couple of years, the patch remains vibrant, healthy and wonderfully scented. It does require a little effort, however the aroma and the taste of the mint makes it all worthwhile. After the work, you even have a great excuse to make yourself a steaming cup of mint tea. If the weather is too hot, there is no problem, either. Instead of tea, how about an ice cold glass of mint julep? In fact, you can even add a few leaves to a tall glass of iced tea.
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Posted in food and plants and tagged cat mint, catnip, invasive, lemon balm, lemon mint, mint, peppermint, preventing spread, spearmint by rextrulove with 18 comments.