Romaine lettuce contain elongated, thick leaves which are crisp and savory, and hold these qualities well after harvest. Very heat resistant, the plants are slow to bolt; ideal for either fall or spring. It is an edible vegetable that typically grows as an annual, Romaine lettuce is known for growing to a height of approximately 7.8 inches with a stemless habit. If you grow only one vegetable other than tomatoes, it should be lettuce. Lettuce is so easy, takes up little space, and you can even grow it among flowers.