I planted garlic last weekend, expecting it to come up in the spring, as indicated here. Then I went away for a few days. When I came back today, it was already sprouting. Should I be alarmed? Is this normal? Is this what planting garlic means in the era of global warming?
I've had garlic sprout in the fall myself when the weather turns quite warm after a cold spell (in November in my area). This is normal but not-helpful behavior for garlic in the North (I'm assuming that you garden in a colder climate because you haven't indicated a location in your profile). So, what to do about the sprouted garlic?
It's okay if the foliage freezes, which will of course happen over the winter, but that does set the plant back a bit in the spring. What's worked best for me in preventing this is heaping soil over the newly sprouted foliage. This appears to protect the foliage from the colder air until it's covered by snow. You could also apply a thick layer of mulch instead of soil, if you wish.
Next year, I recommend waiting until very late October to mid-November to plant your garlic (depends on how far north you are/your agricultural zone, of course).