Peppermint is an incredibly adaptable plant, but ideally, it prefers a cool, moist climate with well-draining, loose, organically rich soil. You can conduct a soil test through your local extension office to determine the nutrient balance and pH of your soil. The soil pH should be between 5.5 and 6.0. It will tolerate sandy or clay soil provided it’s kept sufficiently moist.
Peppermint will thrive in a part shade to full sun location. Variegated cultivars require protection from the heat of the midday sun, or the white and cream areas of the foliage can become scorched. This is particularly important if you’re growing in a region with temperatures that go above 85°F. There’s one thing to keep at the front of your mind when growing peppermint: water. While the plant can forgive poor soil or inadequate sunlight, dry soil spells disaster. That said, the oil concentration is stronger if you let the soil dry out a little between waterings as harvest time nears. If you live in a hot or dry area, add a layer of organic mulch like grass clippings, straw, or leaves. This will help the soil to retain moisture.
Always water at the base of plants and not on the foliage to prevent fungal infection. Water in the morning if you can, so that any water that splashes onto the leaves has time to dry out over the course of the day. After flowering, in mid-June to late July, you’ll start seeing runners. This means the plant is sending out stolons to spread itself around. These are different from standard stems because they have fewer leaves. They’ll form roots wherever a bud touches the soil. That’s when it’s time to be vigilant. Unless you want a ton of new plants, you’ll need to start trimming, pulling, and restricting its spread. Pull up any suckers and clip stolons off the plant when you see them. Every few years, you may want to dig up half of the plant and either put it in a new place or use up all the leaves.
That’s why growing mint in a container is such a good idea. Container growing will limit how far it can spread, and prevent it from taking over your garden. A two or five-gallon container is ideal to accommodate the plant’s mature size. You can also bury your container in the ground, leaving the top two inches of the pot above the ground. In this case, use a five-gallon pot. Be aware that the soil in containers tends to dry out much more quickly than it does in the garden – so be vigilant with your watering schedule. Peppermint can also grow indoors in containers with one caveat: it will rapidly outgrow small pots.
Peppermint doesn’t require much in the way of fertilization. Beyond working in some well-aged compost at planting time, you can give your plants an annual dressing of compost, or nitrogen rich-fertilizer to increase the foliage a few weeks prior to blooming.