How to Grow Mountain Mint in Australia

Mountain mint (Micromeria thymifolia), also sold as Balkan mint, is a small woody-based perennial of the mint family, Lamiaceae, grown for its strongly minty leaves. It is neither a true mint (Mentha) nor a North American mountain mint (Pycnanthemum), and it grows as a tidy clump that does not run. The usual mistake is burying the dust-fine seed, which needs light to germinate.

Three mistakes that matter

1. Covering the seed. The seed needs light to germinate, so seed buried under soil may never come up. Press it onto the surface instead, as Sowing Seeds describes, and keep the surface damp until seedlings show.
2. Treating it like true mint. Moist, rich soil in part shade suits Mint, but it can give mountain mint soft growth, weak flavour and rotting roots. Grow it hot, dry and lean, in the sharp drainage of its limestone home ground.
3. Never trimming it. Left alone, the stems turn woody and the clump opens up and sprawls. Trim it lightly after flowering and whenever you pick, as Trimming and Shaping explains, so it stays dense and leafy.

When to plant

The seed germinates best with the soil at 20 to 23°C, so most zones sow in spring and again in early autumn. One sowing is enough for years, because mountain mint is a long-lived perennial.

Finish autumn sowings by the end of March in temperate and Mediterranean gardens, and by about Anzac Day in subtropical and arid ones. Outside the window, start seed in a tray indoors or on a seedling heat mat.

Site, soil and setup

In the wild, mountain mint grows in limestone cracks and between rocks in the Balkans and Hungary.

Because it stays put for years, mountain mint sits outside the vegetable rotation. On heavy clay, read waterlogged soil before planting.

Container growing

Mountain mint suits a pot, where you control the drainage completely. Choose a pot at least 25 cm across; a standard 250 mm pot holds about 8 L. Fill it with premium potting mix and add a few handfuls of coarse sand or grit. The store sells one mountain mint, and at 20 to 40 cm tall it suits a pot as it is.

• Water: when the top few centimetres of mix feel dry, then soak until water runs from the drainage holes.
• Feed: fish and seaweed blend at half strength, about 12.5 mL per 9 L, fortnightly from spring to late summer.
• Position: the sunniest spot you have, such as a bright balcony, step or courtyard wall.

Sowing Seeds

Start the seed in a covered tray, where tiny seedlings are easy to watch, or sow direct once the soil is warm. The store's Mountain Mint (Mint Balcan) seeds are Micromeria thymifolia.

Starting in a tray

• Mix the seed with four to ten parts dry, washed sand so it spreads thinly (see how to sow tiny seeds).
• Scatter it over moist seed-raising mix and press it in with a flat hand, leaving it uncovered.
• Water from below or with a fine mist, then cover the tray with vented clear plastic in bright light out of direct sun.
• Keep the tray at the soil temperature When to plant gives; seedlings emerge in 10 to 30 days, often unevenly.
• Thin crowded seedlings with scissors, and move them into their own cells once they can be handled.

Sowing direct

• Rake a weed-free, sunny spot fine, adding grit if the soil is heavy.
• Press the seed and sand mix onto the surface once the soil is warm enough.
• Keep the surface damp with a fine spray until seedlings appear.
• Thin seedlings in stages to 20 to 25 cm apart.

Planting out

Plant tray-raised seedlings out once they are 5 to 10 cm tall. Harden them off first (set them outside a little longer each day, for a week or two, so they adjust to sun and wind). Space them 20 to 25 cm apart and water them in with seaweed solution at half strength, 15 mL per 9 L.

Care by growth stage

Like thyme, it suffers more from too much water than too little. Over-feeding reduces the essential oils that give mountain mint its flavour and aroma.

If growth stalls in very poor soil, scratch in all-purpose controlled release granular (NPK around 14-5-10) once in spring, at half the label rate. Established plants are frost hardy, and wild plants grow at altitudes up to almost 2000 m.

Trimming and Shaping

Trimming keeps the clump compact and leafy. Pruning into old, leafless wood is risky, because bare stems may not reshoot.

• Pinch out the growing tips of young plants so they branch low.
• Shear the whole plant lightly after flowering to promote bushy growth.
• Cut back into leafy growth only, leaving green leaves on every stem.
• Give it one firmer trim each year to keep it compact.
• Replace a plant that has turned woody and sparse with young ones raised from seed or from cuttings.

Companion planting

Mountain mint belongs with herbs that like the same dry, sunny spot and the same light hand with the hose.

Grows well with

• Thyme, which thrives in the same sunny, hot, dry spot.
• Winter Savory, a low, shrubby herb that also wants good drainage and full sun.
• Oregano and Sage, dry-environment herbs for a permanent bed.

Keep apart

• Mint, whose runners can take over a bed and which needs moist soil that would rot mountain mint.
• Thirsty annual vegetables and salad greens, whose watering keeps its roots too wet.

Harvesting Sprigs

Start picking lightly about 10 to 14 weeks after sowing, once the plant is bushy and has leafy stems to spare.

• Pinch or snip the soft tips as you need them.
• Take sprigs from all over the plant, so it stays even.
• For drying, cut whole stems, flowers included.
• Keep watering steady through picking, as for the last care stage.

Stand fresh sprigs in a glass of water on the kitchen bench and top it up as needed. To dry, hang small bunches in a warm, airy spot out of direct sun for 10 to 14 days, until the leaves are brittle. Crumble the leaves and flowers into sealed jars, where they keep for 6 to 12 months. Condensation inside a jar means they need more drying.

Use the leaves as you would thyme, winter savory or oregano in savoury dishes; in the Balkans they are also brewed as a herbal tea.

Common problems

No seedlings after a month. Seed covered too deeply, sown into cool soil or allowed to dry out often fails; see Three mistakes that matter. Read more

Tall, floppy seedlings. Seedlings stretch towards the light when a tray sits in too much shade, so move them into bright light as soon as they emerge. Read more

Plants collapse after rain. Mountain mint does not tolerate wet roots, so plants in heavy clay or soggy mix can rot at the base. Replant on a mound or in a gritty pot.

Weak flavour. Shade, rich soil and regular feeding give soft growth with less of the minty oil, so move plants into full sun and stop feeding.

Pests and diseases

No Australian record names a pest of mountain mint itself, so watch for these general pests of its relatives and of young seedlings.

Aphids (Aphididae). Small green or yellow sap-suckers crowd onto soft new tips and leave them sticky and twisted. Squash small groups or knock them off with a strong jet of water. Read more

Two-spotted mite (Tetranychus urticae). Numbers build quickly in hot, dry weather, and their feeding causes fine yellow stippling, starting on the leaf undersides. Coat the undersides with insecticidal soap, following its label and not in hot weather, and avoid broad-spectrum sprays that kill predatory mites and ladybirds. Read more

Slugs and snails, including grey field slug (Deroceras reticulatum). They feed at night and after rain and can chew young seedlings to the ground. Search with a torch about two hours after sunset. Read more

Damping off (Pythium species and Rhizoctonia solani). Seedlings rot at soil level and topple over, most often in wet, crowded trays. Sow thinly into fresh mix, avoid overwatering and thin crowded seedlings. Read more

Prevention first

• Sow in fresh seed-raising mix, in clean trays.
• Take the tray cover off the day the first seedlings show.
• Check the undersides of leaves every week through hot, dry spells.
• Set citrus rind halves near seedlings and collect the snails under them before dark.

Tips

1. Plant it in a gap in a sunny stone wall, between paving stones or along a path, where brushing past releases its scent.
2. Leave some stems to flower in summer: bees work the small white flowers.
3. In the tropics and humid subtropics, from Darwin to Brisbane, grow it in a pot you can move under cover during long wet spells.