Requires a well-drained moisture retentive soil[1, 16, 37]. Prefers a calcareous soil[37]. Prefers a pH in the range 6 to 7.5[200]. Prefers a rich loamy soil[1]. A light soil and a sheltered position is best for early sowings[1]. Peas have long been cultivated as a food crop and a number of distinct forms have emerged which have been classified as follows. A separate record has been made for each form:- P. sativum. The garden pea, including petit pois. Widely cultivated for its sweet-tasting edible immature seeds, as well as the immature seedpods and mature seeds, there are many named varieties[183] and these can provide a crop from May to October. P. sativum arvense. The field pea. Hardier than the garden pea, but not of such good culinary value, it is more often grown as a green manure or for the dried seeds. P. sativum elatius. This is the original form of the species and is still found growing wild in Turkey. P. sativum elatius pumilio. A short, small-flowered form of the above. P. sativum macrocarpon. The edible-pod pea has a swollen, fibre-free and very sweet seedpod which is eaten when immature. The garden pea is widely cultivated and there are many named varieties. There are two basic types of varieties, those with round seeds and those with wrinkled seeds. Round seeded varieties are hardier and can be sown in the autumn to provide an early crop in May or June, wrinkled varieties are sweeter and tastier but are not so hardy and are sown in spring to early summer. Within these two categories, there are dwarf cultivars and climbing cultivars, the taller types tend to yield more heavily and for a longer period but smaller forms are easier to grow, often do not need supports and can give heavier crops from the area of land used (though less from each plant). Cultivars developed for their edible young seeds tend to have pods containing a lot of fibre but some cultivars have now been selected for their larger and fibre-free pods - these cultivars are harder to grow for their seed, especially in damp climates, because the seed has a greater tendency to rot in wet weather. Peas are good growing companions for radishes, carrots, cucumbers, sweet corn, beans and turnips[18, 20, 201]. They are inhibited by alliums, gladiolus, fennel and strawberries growing nearby[18, 20, 201]. There is some evidence that if Chinese mustard (Brassica juncea) is grown as a green manure before sowing peas this will reduce the incidence of soil-borne root rots[206]. This species has a symbiotic relationship with certain soil bacteria, these bacteria form nodules on the roots and fix atmospheric nitrogen. Some of this nitrogen is utilized by the growing plant but some can also be used by other plants growing nearby[200]. When removing plant remains at the end of the growing season, it is best to only remove the aerial parts of the plant, leaving the roots in the ground to decay and release their nitrogen.