When we buy garlic, they usually make us to buy 2 for $1. The problem is we can never finish them in time before they turn black! We end up throwing them away. Here is a tip of what I usually do to make sure we don't have to dump them. You can do this with ginger or green onions.
Put them in the food processor
Put them in a sandwich bag. Make sure to make them flat. Put them in the frezzer. When you need to use garlic, just break a small piece. (this is why you have to make sure to put them in a thin layer in a sandwtch bag)