Herbs serve many purposes in the garden. Aside from their uses in cooking, crafts and herbal remedies, their foliage and flowers add color and interest to the garden, sometimes attracting butterflies and birds as well.
Starting Seeds Indoors
Some herbs don't tolerate cold temperatures well, and if you're starting from seed, you'll want to start these plants indoors, says Jo Ann Gardner in her book "Living with Herbs." The best time to start seeds indoors depends on the herb, since germination times vary. For example, start lemon balm indoors 10 to 12 weeks before the last frost, basil and sage six to eight weeks and chamomile four to six weeks.
Starting Seeds Outdoors
Planting outdoor seeds revolves around the last frost date in your area, with some herbs---arugula, chamomile, chervil and cress---going into the ground a week before the final frost. Sow borage, coriander and dill the week after the last frost date.
Transplants
Other herbs, such as parsley, don't grow as easily from seed, or you may wish to purchase transplants. As with sowing seeds, keep in mind the best date to move your herbs into the garden based on their cold tolerance. As the North Carolina Cooperative Extension points out, many herbs originated in the Mediterranean region and don't like cold. Transplant these after the risk of frost.
Source: http://www.ehow.com/facts_7242751_time-plant-herb-garden.html