How to Grow Manuka in Australia

Manuka (Leptospermum scoparium) is an evergreen, twiggy shrub of the myrtle family (Myrtaceae). It is grown for its aromatic leaves and masses of white, sometimes pink-tinged flowers that bees love. It grows wild along creeks from the NSW south coast to Tasmania and in New Zealand, so it takes frost and damp ground. The mistake most growers make is burying the fine seed, which sprouts best pressed onto the surface.

Three mistakes that matter

1. Burying the seed. Manuka seed is very fine, and a covering of mix can leave a tray bare for weeks. Press it onto damp seed raising mix and add no more than the finest sprinkle on top, as set out under Sowing Seeds.
2. Cutting back into bare wood. Old, leafless stems may reshoot poorly, so a hard cut on a leggy shrub risks leaving a dead framework. Trim lightly every year after flowering instead, starting in the first year, as under Trimming and Shaping.
3. Missing the first webbing. Teatree web moth caterpillars bind shoot tips into nests of silk and droppings, and they can strip and even kill a young plant. Check twiggy shoots often and clear nests while they are small, as under Pests and diseases.

When to plant

Manuka seed germinates best at about 20 to 25°C, so sow when days are reliably mild. In a cool spell, start the tray on a seedling heat mat. One sowing is enough, because each plant is a permanent shrub. Seed-raised plants can flower from their second full growing season, and some take longer.

In frosty districts, raise seedlings under cover and plant them out after the last frost, around Melbourne Cup weekend in many cool gardens. A tray that reaches planting size in autumn stays in its pots, sheltered, until then, which can mean a full year from sowing.

Site, soil and setup

Manuka puts up with poor soil, coastal wind and damp ground, but it flowers best in a bright, open spot.

No rotation is needed. Give each shrub room to spread 1 to 2 m wide. Most garden plants reach about 2 m high, though wild plants can grow 5 m tall. For help reading a soil test, see soil pH explained.

Container growing

Manuka can be grown in a large pot. Use a pot at least 40 cm wide, about 30 L, with drainage holes. Fill it with native potting mix, or premium potting mix with about a fifth coarse sand mixed through.

• Watering. Water when the top few centimetres of mix feel dry, and never leave the pot standing in water. See watering pots through summer.
• Feeding. Give worm casting liquid diluted to weak tea colour once a fortnight in spring and summer, and nothing in winter.
• Position. Full sun to part shade, shaded in the first summer as under Transplanting.

Sowing Seeds

Start manuka in a punnet or seed tray under cover, where the fine seed and tiny seedlings can be watched every day.

Starting under cover

• Fill a punnet with fresh seed raising mix, with up to a fifth coarse sand added for drainage, and water it before sowing.
• Mix the seed with a pinch of dry sand and scatter it thinly, as in sowing tiny seeds.
• Press it firmly onto the surface. Leave it uncovered, or give it the finest sprinkle of mix.
• Cover the tray with clear plastic and keep it at the temperature under When to plant, in bright, filtered light.
• Mist whenever the surface starts to dry. A tray that dries out can kill the seed.
• Seedlings usually appear in 2 to 4 weeks. Take off the plastic as soon as they do, or they grow weak, and move the tray into sun out of hot afternoon sun.

Transplanting

Before planting, harden seedlings off (a week or two of longer outdoor stays, so leaves toughen), as in hardening off seedlings. Plant each one at the depth it grew in its pot and water it in with seaweed solution at 30 mL per 9 L. Shade young plants on hot afternoons through their first summer.

Care by growth stage

Steady moisture while young and a light hand with feed decide how well manuka grows.

Week ranges run from the sowing date. If growth stalls in very poor sand, a controlled release granular labelled for natives and low in phosphorus, scratched in once after flowering, can help.

Trimming and Shaping

Light trimming after flowering keeps manuka dense and leafy, while a shrub left alone can turn woody and open at the base.

• Pinch out the soft shoot tips of young plants in their first year, so they branch and stay bushy.
• Each year, straight after flowering, shorten the flowered shoots, cutting within the leafy growth.
• Clip a hedge or screen lightly at the same time, rather than in one hard cut later.
• Cut out dead, crossing or webbed shoots whenever you see them, and bin them.
• Wet shoots with myrtle rust first to dampen the spores. Then prune them out, bag them and put them in the general waste bin, never green waste or compost.
• Wash secateurs and gloves with detergent and water after handling rusted shoots.

Companion planting

Manuka suits a native or coastal border alongside plants that share its taste for well-drained soil and little feed.

Grows well with

• Everlasting daisy (Xerochrysum bracteatum), which wants the same light, well-drained soil in full sun.
• Brachycome (Brachyscome species), a native daisy that carpets the soil at the shrub's feet in sun or part shade.
• Tussock grasses (Poa species), natives that like the same moist, low ground once established.

Keep apart

• Lilly pilly (Syzygium species) and other myrtle family plants massed together, which share myrtle rust and pass its spores between them.
• Heavily fed vegetable and rose beds, for the reason under Go easy on phosphorus.

Flowering and Seed Capsules

Flowers open on the new growth from spring into summer. Each leaves a small woody capsule that hangs on long after the petals drop.

• Choose capsules at least 12 months old; the newest ones may hold unripe seed.
• Snip a few short lengths of stem carrying capsules, rather than stripping a whole branch.
• Lay them in an open container in a warm, dry spot.
• Shake out the fine seed as the capsules open, usually within 2 to 7 days.

Store the seed dry in a sealed container, ideally in the fridge at about 4°C; kept dry, it stays viable for several years. Flowering stems can also be cut for the vase, since manuka flowers on new growth.

Is manuka a weed?

No Australian state or territory lists manuka as a declared weed.

Lists change, so check with your state or territory biosecurity agency before planting near bushland.

Common problems

Empty trays. Seed buried too deep (see Three mistakes that matter), a surface left to dry or a cold tray is the usual cause. Read more

Thin, leaning seedlings. Too little light makes seedlings stretch, so move trays into bright, filtered light as soon as they emerge. Read more

Bare, woody lower stems. Skipped trimming leaves a leggy, woody shrub; see Three mistakes that matter and Trimming and Shaping.

Yellowing and dieback in wet ground. Roots rot in soil that stays waterlogged, so move young plants to a mound or a better-drained spot. Read more

Few flowers. Deep shade or skipped trimming is the usual cause, since flowers form on new growth; see Site, soil and setup and Trimming and Shaping.

Sawdust at branch forks. Small piles of sawdust-like frass at the forks or the base mean borers, so squirt methylated spirits into each hole with a small syringe.

Pests and diseases

Most trouble on manuka comes from leaf-binding caterpillars, sap-sucking scale and myrtle rust.

Teatree web moth (Orthaga thyrisalis). Its caterpillars bind shoots into webbed nests packed with brown droppings, worst on fine-leaved tea trees. Pull nests out early with gloved hands or a strong jet from the hose, or cut off webbed stems and bin them. The moths often return, so keep checking.

Scale insects (superfamily Coccoidea). Scale sucks sap from stems and leaves, and a black sooty mould usually follows; manuka is among the more prone tea trees. Hose off light infestations, and spray horticultural oil, mixed to the label, when the young crawlers are moving, usually in early spring. Read more

Myrtle rust (Austropuccinia psidii). Purple spots on soft new leaves turn into bright yellow powdery pustules, and heavy attacks kill shoot tips. Australian agencies list tea trees among its hosts, and New Zealand trials show manuka is susceptible, though field infection there has so far been low. Prune out rusted shoots as under Trimming and Shaping, and check the APVMA register for a fungicide registered against myrtle rust. Report a suspected case to your state or territory biosecurity agency or the Exotic Plant Pest Hotline on 1800 084 881.

Damping off (Pythium species and Rhizoctonia solani). Seedlings pinch in at soil level and topple, rotted by these common soil fungi and water moulds. Keep the mix moist but not wet to lower the risk. Read more

Prevention first

• Sow into fresh seed raising mix in scrubbed trays.
• Look over new shoots every few weeks for webbing, scale and yellow rust spots.
• Space plants so air moves through them and leaves dry quickly after rain.
• Keep young shrubs watered in dry spells, since thriving plants suffer less from web moth.

Tips

1. Seedlings vary in flower colour, from white to the odd pink. To keep a favourite, take semi-ripe cuttings (shoots firm at the base, soft at the tip) in summer, because only cuttings come true.
2. Plant manuka beside a path or gate, where brushing past it releases the scent of the crushed leaves.
3. Use it for a hedge or screen along a boundary, where its twiggy growth makes a dense, low-water barrier.

Due to quarantine restrictions and our shipping policy, we cannot send Manuka Honey Tea Tree seed to Western Australia or Tasmania.