I hang my garlic in bunches outside after harvesting in the fall for 1 week to dry out. Then I bring them into the garage where the temperature is between 45-55F and has daylight. At this time of year green sprouts start to appear on the end opposite the roots. If I cut open a clove there appears to be a green pod in the centre. Now what does this tell me?
Storing garlic depends on a variety of conditions both during the growing season and once harvested. High temperatures before harvest may inhibit natural dormancy and bulbs in storage may start to sprout. Do not overwater or over fertilize garlic during growing season to achieve optimum storage time. Once harvested avoid damp conditions as this can encourage mold and spoilage. Medium sized bulbs store best. The longer garlic is stored, the more critical optimal temperature and humidity proves to be. In general, garlic stores best at 56-58F (13-14C) with a relative humidity of 45-50%. Garlic stored between 40-50F (4.5-10C) is likely to sprout eventually. Anything above 68F (20C) decreases the storage life of garlic significantly. If too dry, garlic will wither more quickly. Green growth in the centre of a clove indicates that the garlic is going to sprout, therefore its storage time is coming to an end. In the latter stages of sprouting a green sprout leaf will emerge from the tip. Experts suggest that garlic tastes better before it begins to sprout but some people do not eat garlic in this condition, especially if it is rubbery.
Source: Meredith, Ted Jordan. The complete book of garlic: a guide for gardeners, growers, and serious cooks. Portland : Timber Press, 2008.