Mint is a fragrant and popular herb, highly valued for its aromatic leaves and diverse culinary uses. Many gardeners cultivate it for its refreshing qualities, hoping to add a vibrant patch of green to their herb beds. However, mint is also infamous for its aggressive growth, quickly earning a reputation as one of the most invasive plants a gardener can introduce. Its ability to spread rapidly can overwhelm adjacent plants and turn a cultivated garden space into a monoculture if left unchecked. Understanding the powerful mechanisms behind this spread is the first step toward successfully managing this herb without sacrificing the rest of your garden.
Understanding Mint’s Aggressive Growth Habit
The secret to mint’s relentless expansion lies in its specialized underground structures called rhizomes. These rhizomes are modified stems that grow horizontally beneath the soil surface, not true roots. They serve as a reservoir for the plant’s energy and possess nodes from which new shoots and roots can sprout. Mint rhizomes typically spread in the top 2 to 8 inches of soil.
As the rhizome expands horizontally, it repeatedly sends up new vertical shoots, allowing the plant to colonize a wide area rapidly. This structure is what makes simple weeding ineffective for long-term control. Pulling the visible green stem above ground often leaves behind the extensive network of rhizomes, which promptly sprout new plants. This requires gardeners to employ specific, targeted containment or eradication strategies.
Containment Strategies for New Plantings
The easiest way to manage mint is to prevent its spread from the moment it is planted. Growing mint in containers is the most straightforward and recommended method for containment. When choosing a pot, select one that is at least 12 inches deep to provide ample room for the plant’s root system.
To ensure the rhizomes cannot escape through the drainage holes, keep the container raised off the soil surface. This prevents any escaping root fragments from rooting into the garden bed below. If the plant grows long runners that hang over the edge, they should be pruned back before they can touch the ground and establish new roots.
Sunk Pot Technique
A more permanent solution involves creating an in-ground barrier using the “sunk pot” technique. This method requires planting the mint within a large container—a pot, bucket, or section of drainpipe—with the bottom removed. The container should then be sunk into the ground so that the rim extends at least 1 to 2 inches above the surrounding soil line. This raised lip prevents surface runners from creeping over the edge and rooting into the adjacent garden soil.
Physical Root Barriers
For gardeners who prefer to plant mint directly into the ground, physical root barriers must be installed. These barriers, which can be made of sturdy plastic, metal, or concrete edging, must be buried to a significant depth to be effective. A barrier extending at least 12 to 18 inches below the soil surface will prevent the rhizomes from tunneling underneath and escaping. Leaving a small portion of the barrier above ground also prevents the mint from spreading over the top of the containment area.
Methods for Removing Established, Unwanted Mint
Eradicating an established, invasive patch of mint requires persistence and a combination of techniques to deplete the plant’s energy reserves stored in the rhizomes.
Mechanical Removal
Mechanical removal involves manually digging out the entire patch, which is best done when the soil is moist. Using a pitchfork rather than a shovel can help lift the long, brittle rhizomes out of the ground in continuous pieces, minimizing fragmentation. It is crucial to sift through the soil and remove every visible piece of the rhizome, as even small fragments can regenerate into a new plant. This process must be repeated regularly, as new shoots will appear for several weeks or months after the initial removal.
Smothering and Solarization
Smothering and solarization are effective, chemical-free methods that use light deprivation and heat to kill the plant. Smothering involves covering the entire area with an opaque material, such as thick black plastic or heavy cardboard, which blocks all sunlight. This deprives the mint of the energy needed for photosynthesis, starving the plant over several months. Solarization uses clear plastic sheeting to trap solar radiation, superheating the soil to lethal temperatures. The mint patch should be cut down and the soil watered thoroughly before covering it with the clear plastic, which is then sealed around the edges. This process must be maintained for four to eight weeks during the hottest part of the summer to kill the rhizomes.
Chemical Control
As a last resort for isolated and persistent patches, a non-selective herbicide containing glyphosate may be used. This chemical works by translocating from the leaves down to the rhizome system, killing the entire plant. To maximize effectiveness, the mint leaves should be damaged before application to facilitate better absorption of the herbicide. Applying the product carefully as a spot treatment ensures that the chemical only targets the unwanted mint and does not affect surrounding plants.