Asparagus season varies based on the climate in which it is grown, though it typically matures in early summer. This is the start of the month of June in northern latitudes such as the US state of Iowa in hardiness zones of 4 to 5, and even earlier in southern US states like Texas with a hardiness zone range of 6 to 9. In tropical regions of the world such as the US state of Hawaii, or warm Mediterranean climates like those of southern Italy and Greece where hardiness zones range from 8 to 10, asparagus season is year round. The height of maturity for the plant, however, only lasts 90 days per season, so crops need to be planted incrementally to receive a steady harvest throughout the year.
The Asparagus species, Asparagus officinalis, is a perennial plant that is actually native to temperate climates and is considered to be a spring vegetable, though it takes three years to mature before it can be relied upon to produce abundant crops that last for up to 15 years or more. The plant has been cultivated at least as far back as 2,000 years ago by ancient Egyptian culture, and it grows in the wild in many regions of the world from China to Peru, which are both leading global producers of the crop as of 2011. Cultivated versions of the plant have been selectively bred over the centuries to produce a more vigorous asparagus season, however, with some types of asparagus crops yielding shoots so large that three of them weigh 1 pound (0.45 kilograms).
Though it takes asparagus a full three years to mature from seed, one-year-old plants known as crowns are usually used to start off a crop. These plants can be harvested lightly in the second asparagus season, though it is recommended that this only be done for three to four weeks during the height of their growth. In the third year and any subsequent years, asparagus crops can be harvested as soon as they mature in spring and early summer. If the plant is allowed to grow too long into the summer without harvesting, it will go to seed and no longer produce edible stems until the following year.
Two other types of asparagus that are widely grown aside from the typical green variety are white asparagus and purple asparagus. These strains have the same asparagus season for harvesting, and only differ in appearance and size. White asparagus is produced by keeping the stems of the plant buried under mounds of dirt which prevents them from being infused with green chlorophyl from interaction with sunlight, and gives the plant's shoots a more mild and softer texture. Purple asparagus was first grown in Italy and is a larger than normal strain with a sweeter taste. It is a hybrid plant where the spear edges of the stems are noticeably purple and is named Violetto d/Albenga after the Albenga north-western region of Italy situated along the Gulf of Genoa.