One of the three plants described here is true spinach (Spinacia); the other two are warm-season vegetables used as substitutes for the real thing, which needs cool weather to succeed. All are grown for their edible leaves, used raw or cooked. All do best in rich, well-drained soil.
True spinach. This is the cool-season annual Spinacia oleracea, a member of the amaranth family (Amaranthaceae). It probably originated in southwestern Asia. All zones. Spinach matures slowly during fall, winter, and spring; long days of late spring and heat of summer make it bolt (go to seed) quickly. For a spring harvest, sow seeds in earliest spring. Choose heat-tolerant selections that are slow to bolt, such as 'Avon' (44 days from seed to harvest), 'Bloomsdale Long Standing' (48 days), 'Crocodile Hybrid' (46 days), 'Indian Summer' (39 days), 'Space' (39 days), or 'Tyee' (38 days). For fall and winter harvests, sow seeds four to eight weeks before the first expected fall frost. Plants will survive freezing temperatures and can be harvested through the winter. Look for disease-resistant, cold-hardy selections, such as 'Bloomsdale Long Standing', 'Dixie Market' (45 days), 'Melody' (42 days), 'Python' (35 days), 'Racoon' (36 days), and 'Winter Bloomsdale' (47 days).
Sow seeds thinly in rows spaced 112 ft. apart, or scatter them over a wide bed; cover with 12 in. of soil. Thin seedlings to 46 in. apart. There are two ways to harvest. You can pinch off only the large outer leaves when they are 36 in. long, allowing the plant to produce new foliage from its center. Or you can cut the entire plant at soil level when it reaches 46 in. wide.
New Zealand spinach. Native to New Zealand and Australia, Tetragonia tetragonioides belongs to Aizoaceae, a family of succulent plants. It is an evergreen perennial in the Coastal and Tropical South but goes dormant after a frost. Elsewhere it can be grown as a summer annual.
Sow seeds in early spring after danger of frost is past; thin established seedlings to 1112 ft. apart. Plants reach maturity about 50 days after sowing; they are 12 ft. tall, with spreading form. Harvest greens by plucking off top few inches of tender stems and attached leaves; a month later, new shoots will have grown up for another harvest. New Zealand spinach tolerates heat and drought but also thrives in cool, damp conditions.
Malabar spinach. Basella alba is a native of India; it belongs to the family Basellaceae. Perennial vine in the Tropical South; grown as an annual elsewhere. It needs night temperatures above 58F and will not survive frost. There is an especially attractive red-stemmed form.
Sow seeds in early summer; thin established seedlings to 1 ft. apart. When young plants are about 1 ft. high, train them on wires or a trellis. At 2 ft. high, pinch out a few inches of stem tip (harvesting any young, tender leaves) to encourage the plants to branch and form more stems. Vine grows about 4 ft. tall. As leaves reach full, succulent size (about 4 in. long; 50 to 60 days after sowing), pick them individually. They are bigger and thicker than leaves of true spinach, so you'll need fewer per serving.