Once sprouting is initiated, the cloves will soften slightly and the green shoots can be seen coming through the tip of the clove. The garlic is still perfectly edible when it has sprouted, the only difference being a slight loss in the intensity of the flavour. The green shoots are edible and can even be separated from the flesh and used as a garnish or in a similar way to shalots.
Sprouting is a completely natural process for garlic because the clove acts as the seed for the next generation. We plant our crop in April as this is when the plants naturally want to start growing again. This natural lifecyle takes place so long as the garlic is stored at ambient temperature. However, when stored in a cold, controlled environment, the time until sprouting can be extended, the only problem being that once the garlic is removed from the cold environment, it will sprout within a few weeks. Much of the garlic imported into Australia has come out of cold storage and you may have experienced it spouting not long after you buy it.
Remember that storage in a dark dry place away from excessive heat will maximise the life of your garlic. DO NOT REFRIGERATE. Over exposure to light will accelerate the sprouting process while humid conditions will lead to mould growth.