Serious gardeners may want to try their hand at saving plant seeds, and carrot seeds present a challenge. While it's not difficult to save carrot seeds, it does take two years since carrots are biennial and only flower after two years of growth. The Carrot Museum suggests saving seeds from at least 40 carrots to maintain a good gene pool, though home growers may wish to work on a smaller scale if saving seeds as a novelty.
Grow carrots in your garden during the spring and summer months. In order to save carrot seed, you need to have your own carrot patch.
Keep carrots in the ground in the autumn, instead of harvesting them. The green tops will die down, but the plant will begin to grow again in the spring. To protect the plants during the winter, apply a 3- to 4-inch layer of mulch over the garden bed where your carrots are planted. Do this only if you live in a temperate area.
Dig up the carrots in the fall instead of leaving them in the ground if you live in an area that receives winter frost. Pull the carrots up by their foliage and discard the foliage. Select the healthiest looking roots (or best-shaped carrots) and store these in a root cellar during fall and winter. Place the carrots you're saving in a plastic bag filled with sand, and make sure none of the carrots touch.
Re-plant your carrots in the spring when frost danger has passed and you can work the ground. Follow the same spacing guidelines for planting roots as you do for planting your carrots. If you left your carrots in the ground all winter, clear away the mulch from the garden bed.
Allow the plants to grow all season long. The carrots will flower in the second year, developing broad white flower clusters that resemble Queen Anne's Lace. Wait for the plant to flower.
Cut off the flower clusters when they begin to turn tan. Place the flower clusters in a windowsill until they dry out. Then rub the flower cluster between your hands to open up the flowers and disperse the seeds.
Store carrot seed in a sealed glass jar in a cool room. The Carrot Museum notes that carrot seeds should remain viable for 3 years if stored in this manner.