Growing Tomatillo

The tomatillo belongs to the nightshade family and, despite its name, isn't a tomato but a ground cherry (Physalis). It originally comes from Mexico and Central America, where people have grown it for thousands of years. In Aztec milpa farming it grew between maize, beans and squash. In British gardens it's still a real highlight, and many growers are surprised by how tough it is and how distinctive it tastes.

The tomatillo's most striking feature is its lantern-shaped husk made of papery calyx tissue. This husk wraps the fruit completely and splits open as the fruit ripens. The flesh tastes tangy and savoury, has an apple-like texture and a slightly sticky skin. Mexican cooking relies on tomatillos for salsa verde, green enchilada sauces and hearty stews.

Tomatillos can't pollinate themselves. A single plant won't set any fruit, so you always need at least two plants that flower at the same time. Bees and bumblebees then take care of pollination, and insects love the flowers.

As with all members of the nightshade family, the leaves and stems of the tomatillo are poisonous. Unripe fruit is inedible raw. As soon as a fruit fills its lantern completely, though, you can pick it green and cook it.

Start tomatillos on the windowsill just like tomatoes, because they're sensitive to frost. Sow them from mid-March to mid-April. After about five weeks of growing on and one to two weeks of hardening off, they're ready for the bed. Freshly harvested seeds won't germinate yet; they need a year's rest and then stay viable for about three years.

Sow the seeds about one centimetre deep. At 20 to 27 °C they germinate within one to two weeks, and a clear plastic cover keeps in the warmth and moisture. As soon as the seedlings show their first pair of true leaves, prick them out into individual pots about 9 cm across.

The young plants can only go outside after the last frosts, from mid-May. Before that, put them outdoors in a sheltered spot during the day so they harden off gradually.

Plant tomatillos very deep, so that only 10 to 15 centimetres stick out of the soil. The stem then forms extra roots. The plants grow large and branch out a lot, so they need 80 by 80 centimetres of space. Give each plant a cane as soon as you plant it, because the shoots snap easily under the weight of the fruit and in the wind. Always plant at least two tomatillos, otherwise you won't get any fruit.

Tomatillos love full sun and need at least 6 hours of direct light a day. Too little sun makes the stems soft and noticeably cuts the yield. A sheltered spot is ideal, because the large leaves catch the wind and the plant gets damaged easily in strong gusts.

The soil should be loose, rich in nutrients and free-draining. Tomatillos can't cope with waterlogging at all and respond with root rot. Slightly acidic to neutral soil suits them best.

When it comes to water, the tomatillo is easy-going. It's surprisingly drought-tolerant and handles short dry spells without trouble. Regular watering does, however, give you a much better fruit set. In pots it grows well in containers of 40 litres or more. Use vegetable compost with added garden compost, ideally with a little sand for better drainage.

Among the varieties available, 'Purple de Milpa' stands out: it produces deep purple to almost black, medium-sized fruit with a nutty, spicy flavour and ripens after about 70 days. 'Toma Verde' is the classic Mexican commercial variety with green, sharply tangy fruit, perfect for an authentic salsa verde. If you prefer something sweeter, go for the pale yellow 'Amarylla', a European variety from Poland that also works well for jams and mild salsas. 'Grande Rio Verde' gives you particularly large green fruit and a generous yield.

Watering tomatillos is less fussy than watering tomatoes. Once a week is usually enough, a bit more often in hot weather. Fruit set is much better when the soil stays evenly moist, but the plants shrug off short dry spells. Waterlogging is the only thing you really need to avoid.

As medium feeders, tomatillos often manage without extra feeding in well-composted soil. A monthly dose of organic vegetable fertiliser won't hurt, though. Potassium-rich fertilisers encourage fruiting, while too much nitrogen tends to produce lush leaves instead of fruit.

You don't need to pinch out side shoots on tomatillos, and gardeners don't usually do it. The bushy growth habit is exactly what you want. If you pinch out the growing tip, you encourage branching and make the plant sturdier. Whether you keep or remove the first flower at the Y-shaped fork (the so-called king flower) is up to you.

In a container, you can overwinter a tomatillo somewhere cool and bright at about 10 °C if you cut it back by two thirds in autumn. Alternatively, take cuttings with 4 to 5 leaves in summer and keep those through the winter. If you save seed, remember that freshly harvested seeds won't germinate yet; they need at least a year to after-ripen.

Compared with tomatoes, tomatillos usually stay healthy in the garden. Late blight, which hits tomatoes and potatoes hard in wet summers, doesn't affect them.

Viruses are the main threat. Thrips spread tomato spotted wilt virus, and aphids carry mosaic viruses such as turnip mosaic virus or potato virus Y. Infected tomatillos develop mottled, distorted leaves, stay small and produce less fruit. There's no cure. Pull out diseased plants early and only save seed from healthy ones.

Aphids like to cluster on the shoot tips. If there are only a few, hose them off with water, and ladybirds, hoverflies and lacewings will deal with the rest. Colorado beetles hardly touch tomatillos, and their larvae don't thrive on the leaves.

In damp weather, bacterial spot can appear on leaves and fruit; it comes in with the seed. Towards the end of the season, warm dry conditions sometimes bring powdery mildew, with a white coating on the leaves. Give your tomatillos enough space and water at the base so the leaves dry off quickly.