How to Grow Mibuna in Australia

Mibuna (Brassica rapa, Japonica Group) is a Japanese leafy green in the cabbage family, Brassicaceae, grown for its long, strap-shaped leaves. It forms dense clumps of smooth dark green leaves with a light mustard flavour, for salads, light cooking and pickling, and usually copes with frost. The usual mistake is sowing it into lengthening spring days or summer heat, when it often runs to seed before a clump fills out.

Three mistakes that matter

1. Sowing into long days and heat. Rapidly lengthening days, hot spells and dry soil all trigger bolting (running to flower), which ends the leaf harvest. Make autumn the main sowing, and pick spring and warm-edge rows young.
2. Letting the soil dry out. Mibuna grows best in moist soil, and water stress turns the leaves bitter and can push plants to flower early. Water before the surface dries, and mulch around plants grown on for full clumps.
3. Missing the first white butterflies. Cabbage white caterpillars hatch from eggs laid under the leaves and chew ragged holes in young plants. Check leaf undersides twice a week from the seedling stage, or cover the row with fine insect mesh at sowing.

When to plant

Mibuna seed germinates in soil between 10°C and 30°C, and the plants grow best in the mild, damp weather of autumn and early spring. Sow a short row every few weeks, since each clump gives up to about five pickings before it flowers.

At the warm edge of a window, sow into light shade and water daily until the heat breaks. At the cool edge, sow early enough in autumn for plants to size up before midwinter, when short days slow growth.

Site, soil and setup

Moist, fertile soil grows tender leaves quickly, and a pH near neutral keeps clubroot (Plasmodiophora brassicae), a soil disease of brassicas, in check.

Container growing

Choose a pot at least 30 cm wide, since smaller pots dry out too fast; a standard 30 cm pot holds about 13.5 L. It needs a depth of at least 15 to 20 cm and good drainage. Fill it with premium potting mix, never garden soil. The store's one variety, 'Green Boy', grows about 30 cm tall and suits a pot or a trough.

• Water: check daily and water in the morning, because potting mix dries out faster than garden soil.
• Feed: worm casting liquid, diluted to weak tea colour, weekly to fortnightly from the first true leaves.
• Position: full sun through the cool months; move the pot into light shade once the weather warms.

Sowing Seeds

Sow direct where the plants will grow, or raise seedlings in cells and plant them out with the root ball intact.

Sowing direct

• Water the bed the day before, then sow 6 to 10 mm deep. Space rows about 25 cm apart, or 40 cm for full-sized clumps.
• Scatter the seed thinly along the drill, and thin later (see Thinning).
• Keep the surface damp; seedlings usually appear in 4 to 14 days, often within a week.

Starting in cell trays

Cells give a head start while an earlier crop finishes, and keep tiny seedlings away from snails.

• Sow two seeds per cell of seed-raising mix, at the same depth, and keep the stronger seedling.
• Plant out at three or four true leaves, usually 3 to 4 weeks after sowing.
• Harden off (accustom seedlings to sun and wind over about a week) before planting out.
• Water in with seaweed solution at half strength, 15 mL per 9 L.

Care by growth stage

Mibuna grows best in moist soil, and modest feeding matters, because nitrogen-rich growth draws aphids. Weeks count from sowing.

If growth stalls in poor soil, a light dose of all-purpose controlled release granular (NPK around 14-5-10), scratched in at the label rate, can help.

Thinning

Crowded seedlings stretch and compete for water, and damp, packed leaves invite downy mildew. Thin to the spacing that matches how you plan to pick.

• Thin once the first true leaves show, keeping the strongest seedling at each spot.
• For regular pickings of small leaves, finish at 10 to 15 cm apart.
• For larger leaves, leave 20 cm; for full-sized clumps, 30 to 40 cm.
• Snip unwanted seedlings at soil level, so the keepers' roots stay undisturbed.
• Eat the thinnings in a salad: the seed the store sells is untreated.

Companion planting

Good neighbours share the cool season without sharing mibuna's pests, or fill the gaps between slower crops.

Grows well with

• Lettuce, a cool-season salad leaf from the daisy family that the brassica caterpillars do not feed on.
• Parsnips and potatoes, slow crops with room between the rows for a quick mibuna catch crop.

Keep apart

• Mizuna, tatsoi and bok choy, brassicas that share the same caterpillars, aphids and clubroot, so pests move straight across.
• Choy sum and mustard, which host the same cabbage aphid and flea beetles.

Harvesting Leaves

Start picking once plants stand 8 to 10 cm tall, usually about a month after sowing, and keep going until a flower stalk appears.

• Take a few outer leaves from each plant with scissors, leaving the centre to keep growing.
• Pick in the morning, when leaves are crisp; leaves cut in the heat of the day often taste bitter.
• For a whole clump, cut about 5 cm above the soil 6 to 8 weeks after sowing, and it should regrow.
• Snap off flower buds as they form; they are edible raw, or cooked like broccoli.
• Once flowering becomes unstoppable, pull the whole plant while the leaves still taste good.

Refrigerate picked leaves straight away and use them within a week. Young leaves go raw into salads, while larger leaves have a stronger flavour and suit a quick stir-fry, a side dish or pickling. Pickle only by a tested method, such as CSIRO's preserving advice, because vegetables kept without enough acid can carry botulism.

Common problems

Running to seed. A stalk rises from the centre and new leaves shrink; day length, heat and dry soil are the triggers, set out in Three mistakes.

Bitter or tough leaves. Heat, dry soil and age all sharpen the flavour, so water evenly and pick leaves young.

Patchy germination. Seed sown into soil outside the range in When to plant, or into a surface that dried out, comes up thinly. Resow into a shaded, well-watered drill once the weather cools.

Seedlings collapsing at soil level. Damping off is a seedling rot caused by soil organisms, mainly Pythium species and Rhizoctonia solani. It rots the stem at ground level, and the seedling falls over. It thrives in wet soil, so water seedlings lightly, and resow in fresh seed-raising mix in a clean tray. Read more

Pests and diseases

Mibuna shares its pests with every leafy brassica, and caterpillars and aphids head the list in Australian gardens.

Cabbage white butterfly (Pieris rapae) and diamondback moth (Plutella xylostella). Their green caterpillars chew holes and leave droppings in the leaves. Young diamondback caterpillars mine the leaf first, then leave see-through windows. Cabbage cluster caterpillar (Crocidolomia pavonana) lays egg masses under the outer leaves, and its young feed in the heart beneath thick webbing. Rub eggs off the leaf undersides, pick off caterpillars, and use a Bacillus thuringiensis (Bt) spray if numbers build. Follow the label, including its wait before picking. Read more

Cabbage aphid (Brevicoryne brassicae). Blue-grey colonies, coated in a whitish powder, cluster under the leaves and stunt young plants. Hose them off or spray insecticidal soap, and leave papery brown aphid mummies alone, since tiny wasps have parasitised them. Read more

Striped flea beetle (Phyllotreta undulata). These small beetles chew shot-holes in the seedling leaves of leafy brassicas, and the holes enlarge as the leaves grow. Fine insect mesh laid over the row at sowing keeps them off.

Snails and slugs (class Gastropoda). They chew seedlings to the ground and leave large holes and silvery trails, worst after rain. Hunt them by torchlight a couple of hours after dark, and set shallow traps of fresh beer. Read more

Downy mildew (Hyaloperonospora parasitica) and white blister (Albugo candida). In humid weather with heavy dew, downy mildew spreads yellow to pale brown patches over young leaves, with a greyish white growth beneath. White blister raises shiny white blisters under the leaves in the same cool, dewy weather. Thin crowded plants, bin affected leaves, and clear the bed after harvest. Read more

Clubroot (Plasmodiophora brassicae). Roots swell and distort, plants stunt, and they wilt on warm days, worst in acid soil. Pull and bin affected plants, never compost them, and lime and rotate as set out in Site, soil and setup.

Prevention first

• Check leaf undersides and the heart of each plant twice a week for eggs, caterpillars and aphids, lifting any mesh to look.
• Pull brassica weeds such as wild radish and wild turnip, which carry aphids and downy mildew between crops.
• Water in the morning at the base of the plants, not over the leaves.
• Clean soil off tools before working another bed, and never move seedlings out of a bed that has had clubroot.

Tips

1. Anzac Day is a fair marker for the main autumn sowing in the southern zones. Rows sown by then crop through winter, ahead of spring bolting.
2. Because the seed is untreated, a thick sowing in a shallow tray gives quick microgreens with a mild mustard bite.
3. To save seed, let 10 to 20 plants flower together, at least 250 m from any other flowering Brassica rapa. Mizuna, tatsoi, bok choy and turnips are all the same species and cross freely with mibuna.
4. Queensland, New South Wales, the ACT, Victoria, Tasmania, South Australia and the Northern Territory do not list mibuna as a declared weed. In Western Australia the species has gone wild on disturbed ground, so check the state's organism list. Everywhere, pull spent plants before the pods ripen unless you are saving seed.