When to Plant Vegetables by Seed or Seedling
The last frost is the date when you're free to plant vegetable seedlings or direct-sow vegetable seeds into the garden. The last frost date is in late spring, but the date varies from year to year and from location to location. You can find the correct date at the local garden center or from the nearest office of the Cooperative Extension Service.
Transplanting seedlings into the garden
If you have seedlings ready to go into the garden after the soil is ready and sufficiently warmed up, your garden can get off to an earlier start. This timing puts fresh food on the table sooner. Vegetables that you can start early indoors include cabbage, tomatoes, peppers, and eggplant.
Remember, if you start too early, your seedlings may be too big too early, making them a little hard to accommodate and care for — you may even have to start over. Here's a general list to get you started; you can tinker as you get more experience raising various sorts of seeds. Yep, get out your calendar — some counting backwards is in order:
Onions: 12 to 14 weeks before the safe planting-out day (which in the case of onions is 4 to 6 weeks before the last frost)
Broccoli, collards, and cabbage: 5 to 6 weeks before the safe planting-out date (which is after the danger of snow and ice is past but while nights are still chilly)
Lettuce: 5 to 6 weeks before the safe planting-out day (which is 4 to 5 weeks before the last frost)
Peppers: 8 to 12 weeks before the last frost
Tomatoes and eggplant: 6 to 8 weeks before the last frost
Cucumbers and melons: 2 to 4 weeks before the last frost
Sowing seeds directly into the garden
Gardeners generally sow seeds directly in the garden after the last frost, after the soil has warmed up and the weather seems to have settled into an early-summer groove. Direct-sowing in cold and/or soggy soil is a bad idea — it's muddy work for you, and the seeds usually sprout poorly or rot; then you have to start over. Best to wait for the right time.
Though you can buy tools and gadgets to help you with this work, there remains something so primal and satisfying about going out with a seed packet and digging in the dirt with your hands.
Vegetables that you can direct-sow include lettuce, onions, peas, radishes, turnips, beets, cabbage, carrots, beans, corn, parsnips, cucumber, lettuce, and tomatoes (in warm climates).