Vegetables are classified by their growing season, annual, biennial or perennial. Most vegetables grow as annuals, with the cycle from sowing to harvesting completed in one season. Vegetables are further classified as either cool-season or warm-season, depending on how they are affected by temperatures. Common vegetables include cauliflowers, spinach and bulb onions.
Grow cauliflowers as either annuals or biennials. The average head is 8 inches in diameter. The plants grow 18 to 24 inches tall with a spread of up to 3 feet. Cauliflowers are a cool-season crop and hardy to USDA Hardiness Zone 3. Cauliflowers do not do well in high-temperature areas.
Plant cauliflowers in well-drained soil with a pH between 6.5 and 7.5, recommends the "Encyclopedia of Gardening" by the American Horticultural Society. The seeds should be space 2 to 3 inches apart. Seedlings should be spaced 15 to 24 inches apart. Water cauliflowers regularly during the growing period. Mulch around the plants to protect its shallow roots and to combat weeds. Cauliflowers need full sun to grow the biggest heads.
Fast-growing spinach reaches a height between 6 to 8 inches. A cool-season annual crop, spinach can be planted as soon as the ground can be worked in the spring, according to the University of Illinois Extension. Successive plantings can be made throughout the spring until the weather gets warm. In the fall when temperatures average below 75 degrees F, successive plantings can be made until six weeks before the minimum average night temperatures are less than 20 degrees.
Spinach grows best in soil with a pH of 6.0 to 7.5. Plant seeds in rows 12 to 18 inches apart. Seedlings should be spaced to 3 inches apart. Harvest the plants when the leaves are large enough, between five and ten weeks after sowing and once the plants are at least 2 inches tall. Spinach can tolerate light shade.
Grow bulb onions as annuals. The bulbs can be either round, flattened or torpedo shaped. This cool-season crop requires cool temperatures to germinate. Onion types are classified by the sunlight they receive. Long-day varieties, which do better in Northern climates, begin to form bulbs when the daylight ranges from 14 to 16 hours, according to Texas A&M University. Short-day varieties do better in Southern climates when the daylight ranges from 10 to 12 hours.
Onions grow best in soil with a pH of 5.5 to 7.0. Plant either seeds, seedlings or small bulbs, called sets. The planting site should be weeded regularly. Once established, onions need very little water, except during drought conditions.