How to Grow Shiso in Australia

Shiso (Perilla frutescens), also sold as perilla, is an annual herb in the mint family, Lamiaceae. It is grown for its aromatic leaves, flower spikes and tiny seedling greens. It loves the Australian summer and dies with the first frost, so each plant gives one long warm-season harvest. The step most growers get wrong comes first: the seed needs light to germinate, and seed buried like basil often fails.

Three mistakes that matter

1. Burying the seed. Shiso seed needs light to germinate, so seed covered deeply often fails to come up. Press it onto the surface or give it a dusting of fine mix, as Sowing Seeds describes.
2. Sowing into cold soil. Shiso is frost-tender and grows well only above about 18°C, so early sowings sit still or rot and a late frost kills them. Wait for warm soil, as When to plant sets out.
3. Letting every plant set seed. Flowering winds down the leaf harvest, and one plant left to seed can fill a bed with seedlings next spring. Pinch spikes as they form, as Pinching and Harvesting describes.

When to plant

Shiso seed germinates best in soil of 20°C to 25°C, and plants grow well only above about 18°C. Sow once frosts are over and nights stay mild. It is a short-day plant (it flowers as the days shorten), so plants flower from late summer whenever they were sown. Early sowings therefore crop longest, and a second sowing three to four weeks later extends the harvest.

In frost areas, start seed indoors four to six weeks before the last frost and plant out once it has passed. Late sowings flower while still small, so they give a shorter picking season.

Site, soil and setup

Shiso grows in full sun or part shade. In hot inland and western summers, afternoon shade keeps the leaves soft, because harsh sun toughens them and crisps the edges.

Container growing

Choose a pot at least 30 cm wide and 30 cm deep, which holds about 13.5 L. Fill it with quality potting mix and sow or plant straight into it. The variety 'Hojiso' suits pots and a sunny windowsill, and 'Japanese Red' makes a colourful pot on a balcony or border.

• Water: check the mix daily in warm weather and keep it just moist, never soggy.
• Feed: fish and seaweed blend at half strength, about 12 mL per 9 L, every fortnight while picking.
• Position: full sun in cool gardens; out of the hottest afternoon sun in warm ones.

Sowing Seeds

Sow shiso direct where it will grow, or raise it in trays under cover where frost lingers.

Sowing direct

• For better germination, chill seed in moist sand in the fridge for 3 days, then soak it overnight in warm water, as seed treatments explains.
• Scatter seed thinly and press it onto moist soil, or cover with no more than 2 mm of fine mix.
• Keep the surface damp with a fine spray until seedlings appear, usually in 7 to 21 days.
• Thin to 30 cm apart once the first true leaves open.

Starting under cover

• Sow onto seed raising mix in cells, two or three seeds to a cell, and do not bury them. Sowing tiny seeds shows how.
• Keep the tray bright and warm, ideally on a seedling heat mat, and moist but not wet.
• Harden off (gradually accustom seedlings to sun and wind), as hardening off seedlings describes.
• Plant out 30 cm apart once true leaves open and all frost has passed.

Care by growth stage

Steady moisture in free-draining soil decides this crop. Dry soil stunts it, while soggy soil rots the roots.

Shiso is a light feeder, so keep every feed at half strength and skip it when growth is lush. If growth stalls in poor soil, a light dose of all-purpose controlled release granular (NPK around 14-5-10) scratched in around the plants can help. Mulch to hold moisture and keep weeds down.

Pinching and Harvesting

Pinching makes a bushy plant with more leaves, and removing flower spikes holds off the end of the harvest.

• Growing tips: pinch them out as plants grow, so each stem branches.
• Lower leaves: pick them first, working up from the base; shaded lower leaves brown off anyway.
• Flower spikes: pinch them out as they form; young spikes are edible, as Harvesting Leaves describes.
• Seed plants: leave one plant to flower where you want seedlings next year, then pull it out.

Companion planting

Shiso makes a good understory plant beneath taller summer crops, where it takes the light shade they cast.

Grows well with

• Tomatoes, which shade shiso lightly through the hottest part of the day.
• Sweet corn, tall enough to grow shiso beneath, and a good crop to rotate with.

Keep apart

• Bok choy and other short leafy crops, which a tall shiso shades and crowds.
• Lettuce and beans, which share sclerotinia rot and can carry it through a crowded bed.

Harvesting Leaves

Start picking about 8 to 11 weeks after sowing, once plants stand about 20 cm tall and carry several pairs of full-sized leaves.

• Pinch leaves off with a fingernail or snip them with scissors, rather than pulling, which can uproot young plants.
• Pick young leaves for sashimi and salads, and larger ones for wraps.
• Pick young flower spikes and buds to chop as a garnish.
• Collect seed in autumn from the dried spikes of the plant left to flower.

Wrap picked leaves in a damp paper towel and keep them in a bag in the crisper, where they last 2 to 4 days. For longer storage, air dry the leaves until crisp and keep them in a sealed jar.

Use green leaves to wrap sushi, garnish sashimi or wrap grilled meat, and red leaves to colour pickled plums.

Common problems

Seed fails to come up. Seed buried too deep, cold soil and old seed are the usual causes, since shiso seed often stays viable for only about a year. Read more

Plants flower while small. Late sowings meet shortening days and flower young, and very low light can also bring red shiso into flower early. Sow early in the window, as When to plant sets out.

Leaf edges turn crisp and brown. Harsh afternoon sun in hot, dry summers toughens and scorches the leaves, so give plants afternoon shade and steady water.

Pests and diseases

Hot, dry weather favours shiso's main pest, while wet soil and crowding bring on its rots.

Two-spotted mite (Tetranychus urticae). The only pest found in a study of commercial shiso crops around Sydney, it feeds under the leaves and leaves white or greyish streaks. Badly hit lower leaves dry out and turn papery. Hose the undersides of leaves and avoid broad insecticide sprays, which kill the predators that keep mites down. Read more

Perilla leaf moth (Pyrausta panopealis). Recorded in Western Australia, the Northern Territory, Queensland and New South Wales, its caterpillars feed on shiso leaves. Check leaves while picking and remove caterpillars by hand.

Root rot (Pythium, Rhizoctonia and Fusarium species). Recorded on shiso crops in Australia, these soil fungi and water moulds rot the roots, and seedlings collapse at soil level. Wet soil is the trigger, so improve drainage and water less. Read more

Sclerotinia rot (Sclerotinia species). Also recorded on Australian shiso, it causes a water-soaked rot covered in white, fluffy fungus, with hard black resting bodies forming later. Pull out affected plants with the soil around their base and bin them.

Prevention first

• Water at the base in the morning so leaves dry before night.
• Space plants 30 cm apart so air moves between them.
• Grow in free-draining soil or a raised bed, following the advice on waterlogged soil.
• Check the undersides of leaves weekly in hot, dry spells.

Tips

1. Keep self-sown shiso out of paddocks and horse yards. The whole plant is highly toxic to cattle, other ruminants and horses, and flowering plants most of all.
2. Sow a tray of seed thickly and cut the seedlings at their first true leaves, usually 16 to 25 days after sowing, for micro shiso.
3. Store saved seed in a sealed bag in the fridge, and sow it within a year.