Turnip is basically a cool climate crop that is resistant to frost and mild freezes[269]. The plants are very easily grown, provided they grow quickly when young and the soil is not allowed to dry out[264]. They succeed in full sun in a well-drained fertile preferably alkaline soil[200]. Turnips grow best in deep, friable, highly fertile soil with pH 5.5 - 6.8[269]. They are said to prefer a light sandy soil, especially when grown for an early crop in the spring, and dislike a heavy soil[37, 269]. They prefer cool moist growing conditions[16]. Turnips tolerate an annual precipitation of 35 to 410cm, an annual average temperature range of 3.6 to 27.4°C and a pH in the range of 4.2 to 7.8[269]. Temperatures below 10°C cause the plants to run to seed, even if they have not yet formed an edible root[269]. The turnip is often cultivated, both in the garden and commercially, for its edible root. A fast growing plant, it can take less than ten weeks from sowing to harvesting[264]. Its short growing season makes turnips very adaptable as a catch crop[269]. There are several named varieties and by careful selection and successional sowing it is possible to harvest roots all year round. The roots are fairly cold hardy and can be left in the ground during the winter, harvesting them as required. However, they can be troubled by slugs and other creatures so it is often better to harvest them in late autumn or early winter and store them in a cool but frost-free place. This species has long been cultivated as an edible plant and a large number of forms have been developed. Botanists have divided these forms into a number of groups, and these are detailed below. Separate entries in the database have been made for each group. B. rapa. The species was actually named for the cultivated garden turnip with its edible swollen tap root. This form is dealt with on this record. B. rapa campestris. This is the wild form of the species. It does not have a swollen root and is closest to the forms grown for their oil-rich seeds. B. rapa chinensis. Pak choi has long been cultivated in the Orient for its large tender edible leaves which are mainly produced in the summer and autumn. B. rapa dichotoma. Cultivated in the Orient mainly for its oil-rich seeds. B. rapa narinosa. Chinese savoy is another Oriental form. It is grown for its edible leaves. B. rapa nipposinica. Mizuna is a fast-growing cold-hardy form with tender edible leaves that can be produced all year round. B. rapa oleifera. The stubble turnip has a swollen edible root, though it is considered too coarse for human consumption and is grown mainly for fodder and as a green manure. It is also cultivated for its oil-rich seeds. B. rapa parachinensis. False pak choi is very similar to B. rapa chinensis with tender edible leaves, though it is considerably more cold-hardy. B. rapa pekinensis. Chinese cabbages are widely grown in the Orient. The large tender leaves often form a cabbage-like head. B. rapa perviridis. Spinach mustard is grown for its edible leaves. A very cold-hardy plant, and also able to withstand summer heat, it can provide a crop all year round. B. rapa trilocularis. Indian colza is mainly grown for its oil-rich seeds. Grows well with peas but dislikes growing with hedge mustard and knotweed[18, 20]. A good bee plant[108].