Parsley (Petroselinum crispum), well-known as a cool-season crop, is easily grown outdoors in the garden in Zones 5a to 9b. 

Parsley grows best in moist, well-drained soil, in an area that receives full sun for at least 6 hours a day. It is a biennial but usually grown as an annual in the northeast. Considered tricky to get started, parsley seeds can be sown directly in the ground in late spring, taking 4 - 6 weeks or longer to germinate. Results will be improved if you soak the seeds for up to 24 hours in warm water (around 75° F)  before sowing. Plant the seeds ½ to 2 inch apart and ¼ inch deep, in rows 2 feet apart. The germinated plants can later be thinned, if necessary.

Parsley can also be started indoors in winter, 8 - 10 weeks before the last frost, and planted out in late spring when the seedlings are 2 - 3 inches high.  Batches of seeds may be sowed successively from April to November to provide fresh leaves.

Parsley can be harvested continuously throughout the growing season. The outer leaves should be cut 1 - 3 inches above the crown which will in turn encourage new plant growth.

Parsley will overwinter in Zones 7 and higher so you may see it pop up on its own in a northeast garden after a mild winter. In their second year the plants will bolt (form flowerheads). These attractive flowerheads may be cut off or allowed to set seeds which can be saved for sowing next year.

Common curly or French parsley (Petroselinum crispum) is mostly used as a garnish though it can certainly be eaten.  'Champion Moss Curled', 'Banquet' and 'Forest Green' are commonly grown standards.

Flat-leafed parsley (Petroselinum crispum var. neapolitanum) is used mainly in cooked dishes. It is generally considered to be the more flavorful  parsley. There are numerous varieties but 'Plain Italian Dark Green' is a standard and 'Argon' is an improved, disease-tolerant variety with an upright growth habit.

Hamburg parsley (var. tuberosum) root (a vegetable) is grown and used in N. W. Europe but is rarely found in the U.S.A. or Britain. Its flavor is between that of parsley and celeriac (celery root).

Courtesy of the NYBG Plant Information Service