Spearmint container growing guide to prevent invasive spreading in your garden bed every year

Growing spearmint in containers is the most effective way to prevent its notoriously invasive roots from taking over your garden beds. Spearmint, like many mint varieties, spreads aggressively via underground rhizomes, quickly outcompeting other plants. By confining it to a container, you create a physical barrier that stops its spread.

Select a container that is at least 8-10 inches deep and 10-12 inches in diameter. Deeper is generally better for mint as it encourages a more robust root system and reduces the frequency of watering. Terra cotta pots are a good choice because they allow for better air circulation and drainage, which mint appreciates. However, be aware that terra cotta dries out faster than plastic or glazed ceramic. If you choose plastic or glazed ceramic, ensure it has ample drainage holes at the bottom. Avoid containers with very narrow openings at the top, as this can make repotting or dividing the plant more difficult later. For larger plantings or if you want to grow multiple spearmint plants together, consider a larger trough or a repurposed wooden planter box, again, ensuring adequate drainage. You can also "double pot" by placing the spearmint in a smaller plastic pot with drainage holes, and then setting that smaller pot inside a larger decorative container. This makes it easy to lift the inner pot for inspection or to move the plant.

Use a good quality, well-draining potting mix. Avoid using garden soil directly in pots, as it tends to compact and can harbor pests or diseases. A mix designed for containers or a blend of potting soil with some perlite or vermiculite for added drainage is ideal. When planting your spearmint, whether from a nursery plant or divisions, ensure the crown of the plant (where the stems meet the roots) is just at or slightly below the soil surface. Water thoroughly after planting to settle the soil around the roots.

Spearmint prefers consistently moist soil but not waterlogged conditions. In containers, this means you'll likely need to water more frequently than if it were in the ground, especially during hot, dry weather. Check the soil moisture by sticking your finger about an inch or two into the soil. If it feels dry, it's time to water. Water until you see water draining from the bottom of the pot. Overwatering can lead to root rot, so good drainage is crucial. During the hottest parts of summer, you might need to water daily. In cooler seasons, reduce watering frequency.

Spearmint is quite adaptable when it comes to sunlight. It will thrive in full sun (6-8 hours of direct sunlight per day), which often leads to the most vigorous growth and best flavor. However, it will also tolerate partial shade (4-6 hours of sunlight per day) or even light shade. If you live in a very hot climate, providing some afternoon shade can prevent the leaves from scorching.

Mint is not a heavy feeder. Generally, a light feeding in the spring with a balanced, all-purpose liquid fertilizer diluted to half strength is sufficient. Over-fertilizing can lead to lush foliage growth at the expense of flavor and can make the plant more susceptible to pests.