Mint is a fragrant herb valued globally for its culinary and medicinal uses. Despite its popularity, many gardeners quickly discover a significant challenge: its aggressive, fast-spreading growth habit. This vigorous expansion often leads to the herb becoming a nuisance, overrunning garden beds and crowding out less competitive plants. Understanding the plant’s unique biology is the first step toward successfully managing or removing this persistent grower.
Classification: Is Mint Considered a Weed?
Mint is not officially classified as a noxious weed by government agencies, which typically reserve that designation for non-native plants that threaten agricultural crops or natural ecosystems. It is intentionally cultivated and recognized botanically as a perennial herb belonging to the Mentha genus. However, the definition of a weed is subjective, meaning any plant growing where it is not wanted.
In a garden setting, mint functions precisely as a weed because of its invasive nature. Its tendency to spread uncontrollably, outcompete adjacent plants for nutrients and light, and quickly colonize new territory makes it a highly aggressive volunteer.
The Root of the Problem: How Mint Spreads Aggressively
The primary mechanism mint uses for its rapid expansion is a specialized underground stem structure called a rhizome. These fleshy, horizontal runners grow just beneath the soil surface. As a rhizome travels, it sprouts new roots and shoots from its nodes, allowing new plants to emerge far from the original location.
Under ideal conditions, such as moist, fertile soil, mint rhizomes can extend several feet in a single growing season. The plant also uses above-ground runners, known as stolons, which root easily when they touch the soil. This dual-spreading strategy makes simple weeding ineffective, as even tiny fragments of rhizome left in the soil can regenerate into a new, fully established plant.
Strategies for Containment and Management
For gardeners who wish to enjoy mint without sacrificing their planting space, containment is the most effective approach. The simplest method is to grow the herb exclusively in containers, such as pots at least 12 inches deep and wide. Placing these containers on a hard surface prevents any escaping roots from taking hold in the ground below. Alternatively, mint can be grown in a bottomless container sunk directly into the garden soil, creating a physical root barrier.
Using a Root Barrier
For this to be effective, the barrier (made from plastic, metal, or a nursery pot with the bottom cut out) must be buried at least 10 to 18 inches deep. The rim of the container must remain a few inches above the soil line to prevent above-ground runners from rooting outside the barrier.
Cultural Management
Regular physical maintenance can also help manage the plant’s vigor. Frequent harvesting or pruning removes above-ground growth, which limits the energy the plant can produce through photosynthesis. Choosing a planting location that is less than ideal, such as one with drier soil or partial shade, will naturally slow the rate of rhizome expansion compared to a moist, full-sun environment.
Complete Eradication of Established Mint
Removing a patch of established mint requires persistence due to the resilience of its rhizome network.
Physical Removal
Physical removal is the most direct method, demanding the careful digging out of the entire root system using a garden fork or spade. The goal is to lift and remove every piece of the fleshy rhizome, as any small fragment left behind can quickly re-sprout.
Solarization and Smothering
For larger, dense patches, a non-chemical method called solarization or smothering can be employed. This involves cutting the mint growth back to the ground and then covering the area with an opaque material, like black plastic sheeting or thick cardboard, weighed down securely. Blocking the sunlight starves the plant of energy and gradually kills the rhizomes, though this process may take several weeks to a full growing season.
Chemical Treatment
If the infestation is severe and other methods have failed, a targeted chemical treatment may be considered. Herbicides containing active ingredients like glyphosate are effective because they are absorbed by the leaves and translocated down to kill the underground rhizomes. This approach requires careful application directly to the mint foliage, often with multiple treatments, to avoid killing desirable surrounding plants.