You can get already made ground lemongrass in the freezer section at your local grocery stores.
For me, the fresher you can get with your ingredients, the better your dish will taste. And it is so easy to make your own fresh ground lemongrass. Usually, I grind 8 stalks of lemongrass at a time and put them in several small ziplock bags.
A stalk of lemongrass has white part in at the head and green part at the end of the stalk. Slice about 1/6 – 1/8 inch start from the white stalk until almost half of the green stalk.
Then use food processor to grind it until it is quite fine. (Blender won’t work. Sorry!)
Place them in several small ziplock bags and freeze them. Done!
Tips: Put 1/2 cup lemongrass in each bag, flatten them out. It is easier for you to break it whenever you need it. Plus, it defrost faster too.