How to Grow Mizuna in Australia

Mizuna (Brassica rapa var. nipposinica) is a Japanese leafy green in the cabbage family, Brassicaceae, grown for feathery leaves that regrow after cutting. A regular in baby leaf mixes with a mild, mustardy bite, it grows through the cool months in every Australian zone. The usual mistake is sowing it into warming spring weather, when it runs to flower before it has given much.

Three mistakes that matter

1. Sowing into spring heat. Lengthening days and hot, dry weather trigger flowering (bolting, when a plant runs to seed), and the leaves turn bitter. Favour the autumn windows in When to plant.
2. Letting the soil dry out. Mizuna needs steady moisture. Dry spells make the leaves bitter and push plants to flower sooner. Water whenever the top 5 cm of soil is dry, as set out in Care by growth stage.
3. Cutting too low. Shearing the clump right at soil level can leave nothing to regrow from. Cut about 5 cm above the soil, or pick the outer leaves and leave the centre growing, as described in Harvesting Leaves.

When to plant

Mizuna seed germinates in soil from 10°C to 30°C, so soil temperature seldom holds back an autumn sowing. Heat and day length set the season instead, so sow for plants to grow through the cool months. For a steady supply, sow a short row every few weeks rather than one large patch.

In Canberra, skip sowing in May and June, when days fall below 10 hours. At the warm end of any window, sow in light shade and keep the bed moist.

Site, soil and setup

Sow mizuna where beans, peas or tomatoes grew, not after other brassicas. Where clubroot has appeared, grow no brassicas in that bed for at least four years.

Container growing

Mizuna is compact and quick, so a trough of mixed colours by the back door puts salad leaves within reach. Use a pot of at least 10 L, 30 cm across and 15 to 20 cm deep, with drainage holes and premium potting mix. The upright 'Flame Trees', and 'Red' and 'Garnet', which are sold for baby leaf, suit pots well.

• Water: pots dry out faster than beds, so check them daily in warm weather and water before the mix dries out.
• Feed: from three weeks after sowing, fish and seaweed blend at 25 mL per 9 L, fortnightly.
• Position: full sun in the cool months; move the pot into light shade during warm spells.

Sowing Seeds

Sow mizuna direct where it is to grow, which suits a crop cut young, or raise seedlings in trays to plant out.

Choosing a variety

Some red and purple selections sold as mizuna are mizuna-type mustards (Brassica juncea), so read each product page. They grow the same way, but some taste hotter. For true mustard greens, see the Mustard guide.

Sowing direct

• Rake the bed to a fine surface and water it the day before.
• Sow thinly in rows 20 to 30 cm apart, 6 to 10 mm deep.
• For baby leaf, scatter the seed over a patch instead and rake it in lightly.
• Keep the surface damp; seedlings usually emerge in 4 to 12 days.
• Thin the seedlings as set out in Thinning.

Starting in trays

• Sow two or three seeds per cell of seed-raising mix, 6 mm deep.
• Snip all but the strongest seedling in each cell at mix level.
• Plant out at 3 to 4 weeks, once seedlings have 3 or 4 true leaves.
• Harden them off first (a week of gradually longer spells outdoors); see hardening off seedlings.
• Water them in with seaweed solution at 30 mL per 9 L.

Care by growth stage

Steady moisture keeps the leaves tender and mild, and a light, regular feed keeps a cut clump regrowing. Weeks count from sowing.

Water at the base early in the day, so the leaves dry quickly and mildew has less chance. If growth stalls in poor soil, a light dose of all-purpose controlled release granular (NPK around 14-5-10) scratched into the soil can help. Go easy on nitrogen beyond that, since soft, sappy growth draws aphids.

Thinning

How far apart to thin depends on how you plan to pick: close for baby leaf, wider for full clumps to cook.

• Thin in two stages: first once seedlings have their first true leaves, then again as the leaves touch.
• Snip unwanted seedlings at soil level rather than pulling them, to spare the roots of their neighbours.
• Remove yellowing lower leaves so air moves around the base.
• Snap off flower stems as they form, which keeps leaves coming a little longer.
• Pull finished plants with their roots, so no stumps carry disease on.

Companion planting

The best neighbours for mizuna come from other plant families, which share neither its caterpillars nor clubroot.

Grows well with

• Lettuce, a quick, cool-season salad crop that is not a brassica.
• Dill, whose strong scent may help to confuse egg-laying cabbage white butterflies.
• Coriander, another strongly scented herb that cabbage white butterflies are said to avoid.

Keep apart

• Bok Choy and Chinese Cabbage, the same species, which share its caterpillars, aphids, white rust and clubroot.
• Mustard, a host of cabbage aphid and a brassica for the rotation to avoid.

Harvesting Leaves

Start picking baby leaves 3 to 4 weeks from sowing, once plants are 8 to 10 cm tall. Full clumps are usually ready in 5 to 7 weeks.

• Pick in the morning, when the leaves are crispest.
• For single leaves, take the outer ones and leave the centre growing.
• For a bigger picking, cut the whole clump 5 cm above the soil and let it regrow.
• Pick the young flowering stems too, and cook them like broccoli.
• Once flowering takes over, cut whole plants while the leaves still taste good.

Wash and dry the leaves, then store them in a perforated plastic bag in the fridge, where they keep for up to a week. For longer keeping, blanch and freeze them as you would spinach. Eat young leaves raw in salads, and add the larger, stronger-flavoured ones to stir-fries and soups.

Common problems

Bitter or coarse leaves. Big, older leaves are stronger and tougher, and leaves picked in the afternoon heat often taste bitter, so pick younger and in the morning.

Patchy or no germination. Seed sown too deep, a surface left to dry out, or soil outside the range in When to plant is usually to blame. Resow 6 to 10 mm deep and keep the surface damp. Read more

Seedlings collapsing. Damping off rots the stem at soil level in wet soil, and brassica seedlings may stand on a thin, twisted stem called wire stem. Read more

Seedlings cut off at ground level. Cutworms feed at night and hide in the soil by day, so scratch the surface around the stump to find the caterpillar. Read more

Plants yellowing and wilting on warm days. Clubroot swells and deforms the roots and stunts the plant, mostly in acid soil. Lift affected plants and bin them rather than composting, then lime and rotate as in Site, soil and setup.

Pests and diseases

Mizuna shares its pests with every other brassica, and a look under the leaves twice a week catches most of them early. Use only sprays whose label names leafy brassicas, and keep to any withholding period.

Cabbage white butterfly (Pieris rapae). The white butterflies with grey-black wing spots lay eggs on the leaves, and green caterpillars chew large holes and leave green droppings. Pick the caterpillars off, or spray a Bacillus thuringiensis (Bt) product. Read more

Diamondback moth (Plutella xylostella). Bright green caterpillars up to 10 mm long chew windows in the leaves that tear into holes as the leaves grow. In Queensland they resist several insecticide groups, so rely on Bt, hand picking and mesh. Around Stanthorpe, mid to late summer crops suffer more than early summer ones. Read more

Cabbage aphid (Brevicoryne brassicae). Grey-green aphids up to 3 mm long, coated in whitish powder, cluster under the leaves. Hose them off or spray insecticidal soap, and leave any bronze, swollen aphid mummies, which show tiny wasps at work. Read more

Downy mildew (Hyaloperonospora parasitica). Yellow patches form on the upper leaf with greyish white growth beneath, most often on crowded seedlings in cool, moist weather. Thin plants well, water early in the day and remove affected leaves. Read more

White rust (Albugo candida). Smooth white blisters under the leaves burst to release powdery spores, with yellow-green spots above. It thrives in cool weather with heavy dews, so remove affected leaves, clear old plants and keep brassicas off that bed for three years.

Prevention first

• Cover rows with fine insect mesh from sowing, and lift it from time to time so aphids do not build up underneath.
• Check both sides of the leaves twice a week and crush any eggs.
• Hunt slugs and snails by torchlight two hours after sunset on wet nights, and use iron-based baits if needed.
• Pull wild radish, wild turnip and weedy mustard near the bed, which host brassica pests.

Tips

1. Tuck a short row of mizuna between slower crops such as parsnips or potatoes, and cut it before they need the room.
2. For a home salad mix, sow mizuna beside rocket and red mustards, and cut them together while young.
3. To save seed, let at least five plants of one variety flower together, with no other Brassica rapa crop in flower within 250 metres. Mizuna crosses with bok choy, Chinese cabbage and turnip. Cut the stalks once the lowest pods turn brown and crisp.