Vegetables are classified as warm-season or cool-season according to their tolerance for temperature extremes. Each geographic region has estimated first and last frost dates according to historical weather data. With this advice and an awareness of the climate your vegetables need, you can determine when to plant your vegetables outside for a successful garden.
Warm-season vegetables need the long, hot days that are offered from late spring to early fall. Some vegetables in this category are strawberries, cantaloupe, squash, watermelon, corn and snap beans. When temperatures frequently reach an average of 65 degrees F to 95 degrees F, you may start putting these plants outside.
Contrary to this warm-season vegetables, cool-season plants bear the lower temperatures. Cool-season vegetables grow best with a normal average temperature of 55 to 75 degrees F and usually survive light frosts. Some examples of cool-season vegetables contain beets, carrots, parsnips and other root plants, asparagus, white potato, cabbage, celery, lettuce, onion, spinach, broccoli, cauliflower and artichoke.
Frost dates have been provided as an estimate of when the first and last frost for a geographic area will occur. These dates are essential for determining when to plant outside because some species are more sensitive to frost than others. Warm-season vegetables must be planted outdoors after the danger of frost has passed. Cool-season vegetables are somewhat more tolerant of frost, depending on the species, and the desired planting date fluctuates. Normally, cool-season vegetables may be planted in early spring for harvest later in the spring or in late summer for fall harvest. Vegetables with a brief growing season can be re-planted following harvest.
Direct Seed or Transplant
Some vegetables perform best when planted in the ground straight from seed while others require transplanting. Vegetables that need transplanting may be started inside by seed four to six weeks ahead of the outdoor planting date. The exterior direct-seeding date for vegetables is usually earlier than the exterior transplanting date. However, some vegetable seed species possess particular soil temperature conditions for germination. To adapt to this, seeds may be started inside until the ground temperature is adequate or transplants can be purchased.