Invasive herbs such as mint and lemon balm can outcompete nearby plants through rapid root growth and allelopathy; I planted mint with parsley once, and in less than a month, the mint roots had smothered the parsley's roots. I quickly learned that if I wanted to grow mint, I needed to isolate it.
Root Systems
- Mint spreads via underground runners (rhizomes)
- Lemon balm roots secrete growth-inhibiting chemicals
- Chokes nearby plants' nutrient uptake
Aboveground Traits
- Fast vertical growth shades smaller herbs
- Leaves release allelopathic compounds into soil
- Outcompetes for water and light
You can restrict aggressive herb growth by placing the herb in submerged pots with drainage holes. To do this, sink a nursery pot into a larger container for decorative purposes. This will prevent the invasive rhizomes from escaping. I do this with lemon balm and change the soil every year to avoid root-binding. I also just keep cutting them back to avoid them getting out of control.
Physical Barriers
- Line pots with copper tape to deter rhizomes
- Use fabric root bags inside containers
- Elevate pots to isolate drainage runoff
Maintenance Routines
- Prune roots every 6 months
- Harvest 1/3 of foliage weekly to slow growth
- Replace top 2 inches of soil quarterly
Try vertical gardening with your aggressive herbs! Wall-mounted planters can help you keep mint in check while adding a layer of dimension to movement on your walls and keeping your garden greens in sight. In my kitchen, I have at least three types of mint growing on one wall host, each in its pocket, removed from the others, so there is no cross-contamination of flavors. Note that growing mint this way utilizes space advantageously without losing herb diversity or flavor!
Read the full article: Growing Herbs Indoors: The Ultimate Beginner's Guide
