Two lilac-violet flowers appear among a clump of thin, blade-like vertical leaves. Various small weeds and other plants grow from black soil and are shown in overcast daylight.
Saffron crocus flowers in Osaka Prefecture, Japan
C. sativus thrives in the Mediterranean maquis (equivalent physiognomically to the North American chaparral), and like climates where hot, dry summer breezes sweep semi-arid lands. It can nonetheless survive cold winters by tolerating frosts as low as −10 °C (14 °F) and short periods of snow cover. Irrigation is required if not grown in moist environments such as Kashmir, where annual rainfall averages 1,000–1,500 mm (39–59 in); saffron-growing regions in Greece (500 mm or 20 in annually) and Spain (400 mm or 16 in) are far drier compared to the one cultivated in Iran, for example. Timing is the key: generous spring rains and drier summers are optimal. Rain immediately preceding flowering boosts saffron yields; rainy or cold weather during flowering spurs disease and low yields. Persistently damp and hot conditions harm crops, as do the digging actions of rabbits, rats, and birds. Nematodes, leaf rusts, and corm rot pose other threats.
The plants fare poorly in shady conditions; they grow best in strong sunlight. Planting is thus best done in fields that slope towards the sunlight (i.e., south-sloping in the Northern Hemisphere), maximizing sun exposure. Planting is mostly done in June in the Northern Hemisphere, where corms are lodged 7 to 15 centimetres (2.8–5.9 in) deep. Planting depth and corm spacing, in concert with climate, are critical factors affecting yields. Mother corms planted deeper yield higher-quality saffron, though form fewer flower buds and daughter corms. Italian growers optimize thread yield by planting 15 centimetres (5.9 in) deep and in rows 2–3 cm apart; depths of 8–10 cm optimizes flower and corm production. Greek, Moroccan, and Spanish growers have devised distinct depths and spacings to suit their locales.
C. sativus prefers friable, loose, low-density, well-watered, and well-drained clay-calcareous soils with high organic content. Traditional raised beds promote good drainage. Soil organic content was historically boosted via application of some 20–30 tonnes of manure per hectare. Afterwards—and with no further manure application—corms were planted. After a period of dormancy through the summer, the corms send up their narrow leaves and begin to bud in early autumn. Only in mid-autumn do they flower. Harvests are by necessity a speedy affair: after blossoming at dawn, flowers quickly wilt as the day passes. All plants bloom within a window of one or two weeks.[19] Roughly 150 flowers yield 1 gram (0.035 oz) of dry saffron threads; to produce 12 g of dried saffron (72 g freshly harvested), 1 kg of flowers are needed (1 lb for 0.2 oz of dried saffron). One fresh-picked flower yields an average 30 milligrams (0.46 gr) of fresh saffron or 7 milligrams (0.11 gr) of dried saffron.
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