How to Grow Mint Without It Taking Over the Garden

Mint is the easiest herb to grow and the hardest to get rid of, and both facts have the same cause: it spreads by rhizomes — horizontal stems running an inch or two below the surface, sending up new shoots as they go.

Put one in a border and within two seasons it will be several feet across and threaded through the roots of everything near it. Every fragment left behind grows again.

Containment, properly

A pot at least 12 inches across, with drainage, in ordinary potting mix. That is the whole answer for most people.

If you want mint in a bed:

• Sink a bottomless container or a large pot into the soil.
• Leave the rim standing an inch or two above the surface. This is the step people skip, and mint simply runs over a flush rim and out into the bed.
• Check the edges each spring for runners that have escaped over the top.

Conditions: not the usual herb advice

Most herbs — rosemary, thyme, oregano, lavender — want sun, heat, and sharp drainage. Mint wants the opposite of all three.

• Partial shade. Morning sun and afternoon shade is ideal.
• Consistently moist soil. It grows wild on stream banks.
• Ordinary, moderately rich soil. No need for grit or lean conditions.

Full sun plus dry soil is what gives you small, tough, bitter leaves — and it is exactly what happens when mint is planted in a Mediterranean herb bed alongside plants with opposite requirements.

Varieties

Grow each in its own pot. Mints hybridise and compete, and a mixed container becomes a single vigorous mint — usually apple mint — within a couple of years.

Keeping the leaves good

Two jobs, both continuous:

Pinch the tips. Taking the growing point out of each stem forces the plant to branch from lower buds. Do it from the moment the plant is established, and repeatedly. The difference between a bushy mint and a leggy one is entirely this.

Remove flower buds as they appear. Flowering is the signal that ends tender leaf production — foliage toughens and turns bitter within a week or two. Pinch the buds off and the plant carries on producing leaf for months longer.

Late in the season it is worth letting some flowers open, because mint flowers are excellent for bees and hoverflies. Just do it on a plant you have finished harvesting.

Harvesting

Cut whole stems, back by a third to a half, just above a pair of leaves. The plant branches from that cut and regrows within a couple of weeks.

Picking individual leaves off standing stems gives you bare stalks and no regrowth signal — it is the single most common mistake with mint, and the same one people make with basil.

Cut in the morning after the dew has dried, when the essential oil content is highest.

For storage, mint dries acceptably but loses a lot of its character. Freezing chopped mint in ice cube trays with a little water keeps far more of the flavour.

Dividing

Potted mint becomes a solid mat of woody rhizome within two or three years, and the plant declines — fewer, smaller leaves, and compost that water runs straight through.

In spring: tip it out, cut the root mass into sections with a knife or a spade, discard the old woody centre, and replant a young outer piece in fresh compost. Give the spare pieces away, or throw them away — do not put them on the compost heap, where they will root.

Propagating

Almost trivially easy, which is the other side of the invasiveness:

• Stem cutting in water. A 4 inch stem, lower leaves stripped, in a glass on a windowsill. Roots in one to two weeks.
• Rhizome division. Any piece of underground stem with a growing point.

Both work nearly always. Neither should be done anywhere near an open bed.