The emerged shoots will survive freezing temperatures. Remove the mulch in spring. Poor production can be the result of seed quality, growing conditions, the variety, seasonal conditions and disease. The better the leaf growth before bulbs grow, the bigger the bulb and the cloves will be. Raise the beds to provide a free-draining soil.
Liquid manures are beneficial.
Garlic competes poorly with weeds. Harvest the bulbs when the foliage has died back. Wash the bulbs and roots and leave them to dry outside or undercover for a week or so, depending on the weather. When the bulbs are dry, trim off the roots and store in a dry, cool place. Select the biggest and best bulbs to keep for seed.