How to Grow Tomatillos in Australia

Tomatillo (Physalis philadelphica) is a frost-tender annual in the nightshade family, Solanaceae, grown for tart green fruit wrapped in papery husks. It is the heart of Mexican salsa verde, grows much like a tomato, and has fruited prolifically in Queensland. Most failures trace back to one choice: planting a single tomatillo, which leaves its husks empty.

Three mistakes that matter

1. Planting just one. A tomatillo rarely sets fruit with its own pollen, so a lone plant fills its branches with hollow husks. Plant at least two, and three is safer, close enough for bees to work between them.
2. Feeding for leaves. Too much nitrogen grows a big, leafy bush that is slow to flower and slow to bear fruit. Follow the feeds in Care by growth stage, which switch to potassium once the first flowers open.
3. Picking too late. Fruit left on the plant past its prime turns soft and loses its tang. Pick when the fruit fills its husk and still feels firm, as Harvesting Fruit describes.

When to plant

Sow seed in trays kept at a soil temperature of 21 to 27°C, and plant out once frost has passed and the ground has warmed. Plants flower and fruit until frost, so one sowing is usually enough. Flowers tend to drop on days above 32°C and nights below 13°C, so aim for plants that flower outside the fiercest heat.

At the cool edge, raise seedlings on a seedling heat mat and cover young plants on cold nights, venting covers above 27°C. At the late edge, pick every fruit before the first autumn frost.

Site, soil and setup

Rotate beds: do not plant where tomato, capsicum, eggplant or potato grew the year before, because they share soil-borne diseases.

Container growing

Tomatillos, 'Verde Puebla' included, grow well in a pot of at least 20 L, about 30 cm across, with one plant to each pot. Set two pots side by side for pollination, fill them with premium potting mix, and push in a stake or small cage at planting.

• Watering: check pots daily in hot weather and water deeply whenever the top 2 to 3 cm is dry. See watering pots in summer.
• Feeding: mix a controlled release fertiliser for containers into the mix at planting. Then water on fish and seaweed blend at 25 mL per 9 L fortnightly.
• From first flowers: add liquid potash at the label rate, fortnightly.
• Position: full sun, out of strong wind.

Sowing Seeds

Start tomatillos in trays under cover and plant them out 4 to 6 weeks later.

Starting in trays

• Sow seed 4 to 6 mm deep in seed-raising mix, and keep it moist and at the warmth When to plant gives.
• Seedlings usually appear in 7 to 14 days.
• Once true leaves show, move each seedling to its own small pot, or thin to one per cell.
• Give seedlings bright light so they grow stocky, not leggy.

The seed comes treated with the fungicide thiram. Wear gloves, wash your hands with soap and water afterwards, keep the seed away from children and animals, and never eat it.

Planting out

• Plant out when seedlings are 5 to 10 cm tall or a little more, and before they flower, since flowering transplants establish slowly.
• Harden off (get seedlings used to sun and wind outdoors) over one to two weeks first.
• Set each plant deeper than it grew in its pot: the buried stem grows extra roots, as a tomato does.
• Drive in its stake or set its cage at the same time, as Pruning and Training describes.
• Water in well, then mulch with straw.

Pollination

Each tomatillo flower carries both pollen and stigma, yet the plant largely rejects its own pollen. Bagged away from insects, flowers set no fruit. Bees must bring pollen from another plant, and two 'Verde Puebla' plants pollinate each other.

Where bees are scarce, move pollen by hand between flowers on different plants.

• Dab a small soft brush or cotton bud in the centre of an open flower on one plant.
• Touch it to the centre of open flowers on a second plant.
• Repeat in the other direction every few days while plants bloom.

Care by growth stage

Even moisture and a light hand with nitrogen decide the crop, though established plants cope with short dry spells. Weeks count from sowing and shift with zone and weather.

If you prefer a conventional feed, mix a controlled release granular (NPK around 14-5-10) into the bed at planting. While plants establish, water on an all-purpose soluble (NPK around 23-4-18) fortnightly at half the label rate. From first flowers, switch to a fruiting and flowering soluble (NPK around 15-4-26) at the label rate.

Pruning and Training

Plants grow about 1 to 1.2 m tall and spread 1 to 1.5 m, and any stem that touches the soil takes root. Support keeps fruit clean and air moving; flowers form along every branch, so trim lightly.

• At planting, drive a stake about 1.2 m long some 45 cm into the soil beside each plant.
• Tie the main stem loosely with soft ties, adding more as the plant grows.
• Or set a tomato cage over the plant: tomatillos weigh less than tomatoes, so a standard cage copes.
• Pinch out growing tips to limit spread where space is short.
• Cut back branches that crowd a neighbouring plant, so air keeps moving.
• Lift or trim stems that lie on the soil before they root.

Companion planting

Every tomatillo fruit depends on bees, so the best neighbours are flowers that feed them.

Grows well with

• Sunflower, whose pollen-bearing varieties are excellent bee plants through the season.
• Basil, whose summer flowers give bees nectar if a few plants are left to bloom.
• Marigold, whose small, shallow flowers suit short-tongued bees.

Keep apart

• Tomato, capsicum and eggplant, which share aphids, whitefly and fruit fly with tomatillo.
• Potato, which shares soil-borne wilt diseases.

Harvesting Fruit

Picking usually starts 10 to 14 weeks after sowing. The fruit is ready once it fills its husk and the husk fades from green to tan and splits.

• Pick while the fruit is firm; soft fruit is past its best.
• Snip the stalk with scissors or secateurs, or twist gently: ripe fruit comes away easily.
• Pick every week, since plants keep setting fruit until frost.
• Gather fallen fruit, which keeps ripening in its husk.
• Before the first autumn frost, pick every fruit, ripe or not.

Keep fruit in its husk, one layer deep, somewhere cool and airy, ideally 10 to 15°C, where it can keep for weeks and sometimes months. In the fridge, a paper bag holds fruit for one to two weeks before the skin pits, while sealed plastic rots it fast. Store it away from apples and bananas, whose ethylene shortens its life, or husk, wash and freeze it.

To use, peel off the husk, rinse away the sticky film, then roast or boil the fruit and blend it into salsa verde. Eat only the fruit: the husks, leaves and stems are not edible.

Common problems

Husks with nothing inside. Too few plants, plants set too far apart, or heat, cold or drought at flowering; see Three mistakes and Pollination.

Dark, sunken patch at the flower end of the fruit. This is blossom end rot: calcium reaches fruit only in water, so swings in soil moisture starve it, and even watering is the fix. Read more

White powdery patches on older leaves. Powdery mildew spreads through crowded plants; stake them for airflow and, at the first spots, spray 1 part full-cream milk to 10 parts water. Read more

Plants wilting in moist soil. Roots rot where soil stays wet long after watering; water less often, and grow the next crop in a raised bed.

Pests and diseases

Tomatillos have few serious pests, and the husk shields most fruit.

Queensland fruit fly (Bactrocera tryoni). This native pest of eastern Australia is worst in mid and late summer, after rain. Females sting ripening fruit, and white maggots tunnel through the flesh, which rots. The husk protects only partly, so net plants with fine insect mesh from fruit set and pick up fallen fruit. Read more

Green peach aphid (Myzus persicae). Colonies under the leaves crinkle and curl them and leave them sticky, and aphids can spread viruses that mottle and stunt plants. Hose them off with a strong jet, or spray insecticidal soap. Read more

Silverleaf whitefly (Bemisia tabaci). Clouds of tiny white insects rise when leaves are disturbed, and their sticky honeydew grows black sooty mould. Clear weeds and spent crops that carry it between seasons. Read more

Cutworms (Agrotis species). These grey to black caterpillars hide in the soil by day and feed at night, cutting young plants off at soil level. Scratch around the base of a felled plant and pick out the curled caterpillars. Read more

Verticillium wilt (Verticillium dahliae). Leaves yellow, then plants wilt and die back. This soil-borne fungus infects over 400 plant species in Australia and can survive more than 10 years in soil. No spray cures it, so bin affected plants and rotate beds.

Prevention first

• Rotate beds as Site, soil and setup describes, and clear old plants and fallen fruit after the last picking.
• Water the soil in the morning, keeping leaves dry, and keep plants staked for airflow.
• Check leaf undersides, new growth and stem bases every week.
• Spare the bees that set every fruit: if you must use pyrethrum, spray late in the day, away from open flowers.

Tips

1. A rooted cutting is the same plant as its parent and cannot pollinate it, so raise pollen partners from seed.
2. At season's end, hang a whole laden plant upside down in a dry shed, where the fruit can keep for months.
3. Tomatillos self-sow freely, and Physalis species are environmental weeds in parts of Australia, so clear every fallen fruit when the season ends.
4. To save seed true to type, grow plants 240 to 800 m from other tomatillo varieties, since bees cross them.