From a botanical perspective, mint (genus Mentha) is an aggressively rhizomatous perennial plant. This means its primary mode of territorial expansion is not just through seed or above-ground runners, but through underground stems called rhizomes. These rhizomes grow horizontally beneath the soil surface, rapidly sending up new shoots (ramets) to colonize the area. This growth habit is a key survival strategy, allowing a single mint plant to form a large, genetically identical colony. Therefore, when you plant different mint varieties in close proximity in the same open ground, their root systems do not respect each other's boundaries. They will intermingle and compete directly for space, water, and nutrients.
While the underground competition is the most immediate concern, there is also an above-ground genetic consideration. Different mint varieties can and will cross-pollinate if they flower simultaneously and pollinators, such as bees, travel between them. This genetic exchange does not affect the current plants you have in the ground, as they are clones from the original rhizome cuttings. However, it will affect any plants grown from the seeds produced by those flowers. If you allow your mints to flower and set seed, the resulting seedlings are likely to be hybrids. These hybrids will not be true to the parent variety, displaying a mix of characteristics that may lack the desired flavor, scent, or growth form of the original spearmint, peppermint, or orange mint you planted.
The most significant challenge in growing different mints together is the high probability of one variety dominating and eventually overwhelming the others. Mint varieties have varying levels of vigor. A notoriously vigorous type like peppermint (Mentha × piperita) will often out-compete a less aggressive variety like apple mint (Mentha suaveolens) over a single growing season. Their rhizomes will become thoroughly entangled, making it practically impossible to separate them later. When you harvest a sprig, the scents and flavors may begin to blend, and eventually, the stronger-growing mint may simply choke out the other, leading to a loss of the distinct varietal characteristics you intended to cultivate.
To successfully grow different mint varieties while respecting their botanical nature, physical separation is the only reliable method. The most effective strategy is to grow each variety in its own individual container. Using pots prevents the rhizomes from different plants from intermingling and allows you to control the soil conditions for each type precisely. Ensure the pots have adequate drainage holes and are a sufficient size (at least 12 inches in diameter) to accommodate a season's growth. For a decorative grouping, you can sink these pots into the soil in a garden bed or arrange them on a patio, ensuring the rims remain above ground level to prevent rhizomes from escaping over the top. This method provides the visual appeal of growing them together while maintaining the genetic and spatial integrity of each mint variety.
