Garlic (Allium sativum) is usually grown by separating a bulb into individual cloves and planting each one to grow a new bulb. This has two downsides: It can spread soil-borne diseases and pests, and there is no genetic variation because the garlic is reproduced by asexual means. You can get around one, or both, of these problems by planting garlic seed heads.
About Seed Heads
Though some varieties of garlic are sterile, others, like hardneck garlic (Allium sativum Ophioscorodon group), can produce seed heads borne on long stems called scapes. These garlic varieties are hardy in U.S. Department of Agriculture plant hardiness zones 3 through 8. The seed heads hold tiny garlic bulbs called bulbils, and some also produce flowers that develop true seeds. Both bulbils and seeds may be planted to grow new garlic plants.
Growing garlic from bulbils removes the risk of transmitting soil-borne diseases and pests, and lets you propagate large quantities of garlic. Growing garlic from seeds also eliminates soil-borne problems, and has the added advantage of introducing healthy genetic variation.
After planting bulbils or seeds, it will take at least two to three years before the garlic plants are ready to harvest.
Bulbils: Harvesting and Planting
When garlic develops a scape, it is initially topped by a cluster of bulbils, or bulbils and flowers, covered by a thin sheath. As the plant matures, the bulbils and flowers grow large enough to split the covering sheath. When the sheath splits, the bulbils are ready to harvest. Cut the entire scape and hang it upside-down to dry. Once it's dry, cut the seed head off and store the entire cluster of bulbils in a brown paper bag until you're ready to plant.
Plant bulbils outdoors in the fall four to six weeks before the ground freezes, at the same time you would plant garlic cloves. Set the bulbils about 1 inch deep and space them 2 to 4 inches apart in the garden. Plant with the end of the bulbil that was attached to the scape pointing down, and water thoroughly.
True Seed: Harvesting
Timing is crucial when you're growing garlic from seed. Watch the scapes, which start out curled, as they grow. As soon as the scapes straighten, take a sterilized pair of tweezers and gently peel back the sheath covering the flower head. Use the tweezers to remove as many of the bulbils as possible from the flower head. You can either leave the scapes on the plant for this, or cut the scapes and place them in a jar full of water.
Temperatures above 85 degrees or below 65 degrees Fahrenheit may damage seed production. Setting up a shade cloth can reduce heat damage to scapes still attached to the garlic plants. If you have cut scapes kept in water, move them to a shady spot on hot days or to a warmer location if the weather cools. The flowers are pollinated by insects, so be sure to keep cut scapes outside most of the time, where bees, flies and other insects can reach them.
Harvest the seeds when the seed heads have completely dried, usually in the late fall. Remove the seeds from the seed pods, and soak seeds in a solution of 1 teaspoon bleach in 2 cups water for 20 minutes. Rinse the seeds, and then lay them out on moist paper towels. Place the paper towels and seeds in a plastic bag, and store in the refrigerator for four weeks.
True Seed: Planting
After chilling, start the seed in pots or seed flats filled with a sterile-seed starting mix. Plant them about 1/4 inch deep, and cover the pots or flats with a plastic bag or dome to hold moisture. Set the planted seeds under artificial lights or in a well-lit window, and keep them moist through the winter. Most of the seeds will germinate within two weeks. Seeds harvested from garlic are not very reliable, so don't be surprised if you get low germination rates.
Plant the seedling garlic outdoors in the spring after the danger of freezing has passed. Before planting them in the ground, gradually acclimate the plants to outdoor conditions by setting them outdoors during the day and bringing them in at night every day for about a week. You can also acclimate the plants by setting them out in a cold frame for a week before planting.