I was asked the same question in a PM. This is my lengthy reply.
You are describing the garlic
flower know as the scape. Well, it's not actually a
flower. You will never see a
flower. It will contain tiny garlic bulb-lets if you let it continue to grow. You can
plant the bulb-lets, but they will take 2 years to produce a garlic bulb.
You've stumbled upon the great "scape" debate; to cut or not to cut. Here are arguments for either side:
Cut it:Cutting the scape as soon as it appears is supposed to produce larger bulbs. The theory behind this option is that the garlic reproduces through the cloves and the scape. By cutting the scape the garlic will be forced to expend all it's reproductive energy on making the bulbs bigger so they will survive the winter.
This is the most popular option, and the scapes can be used in cooking as they contain garlic flavor.
Don't cut it:I'm not a garlic
growing expert. There are many people with more garlic
growing experience than me, and one of those people wrote a book on it.
growing Great Garlic by Ron L Engeland is my garlic
growing reference. They have a web site for his gourmet garlic:
Filaree Farms In his book, he goes over the entire
growing season from planting to harvesting. Since he sells his garlic, storage is very important. He describes his theory on balancing size with storability. Basically, his theory is that when the scape un-curls or straightens, hormones in the
plant change, and these hormones improve storage of the garlic. Plus, once the scape straightens, the bulb-lets are big enough that you can use them like you would use garlic cloves. You have to use several bulb-lets to equal one clove, but I've found that the bulb-lets store much longer than the garlic bulbs themselves. Or
plant them to really increase your garlic crop. You can eat the one year old garlic, you just won't get individual cloves. The bulb-lets are not prone to the disease and rot that the cloves are themselves.
So I hope that's enough information for you to decide which side of the fence you are going to sit on the great "scape" debate. Personally, I let the scapes straighten before cutting them.