The tomatillo fruit is surrounded by a paper like husk formed from the calyx. As the fruit matures, it fills the husk and can split it open by harvest. The husk turns brown, and the fruit can be any of a number of colours when ripe, including yellow, red, green, or even purple. Tomatillos are the key ingredient in fresh and cooked Latin American green sauces. The freshness and greenness of the husk are quality criteria. Fruit should be firm and bright green, as the green colour and tart flavour are the main culinary contributions of the fruit.
As with potatoes, other parts of the tomatillo plant contain toxins, and should not be eaten.
Tomatillo plants are highly self incompatible (two or more plants are needed for proper pollination, thus isolated tomatillo plants rarely set fruits).
Fresh ripe tomatillos will keep in the refrigerator for about two weeks. They will keep even longer if the husks are removed and the fruits are placed in sealed plastic bags stored in the refrigerator. They may also be frozen whole or sliced.
The tomatillo is also known as the husk tomato, jamberry, husk cherry, Mexican tomato, or ground cherry, although these names can also refer to other species in the Physalis genus. In Spanish it is called tomate de cáscara, tomate de fresadilla, tomate milpero, tomate verde ("green tomato"), tomatillo (Mexico [this term means "little tomato" elsewhere]), miltomate (Mexico, Guatemala), or simply tomate (in which case the tomato is called jitomate). Even though tomatillos are sometimes called "green tomatoes", they should not be confused with green, unripe tomatoes. (Tomatoes are in the same family, but a different genus.)
Growing in the UK
We grew tomatillos this year in grow bags with our tomatoes, without much success, probably because we had a lousy summer with almost no sun. They were under semi cover but really only started to form fruit at the very end of September giving them no chance to ripen. It seems they need a really long season, or to be grown under glass. We'll try again next year and report back!