If you made this DIY Grass Head before, and you have leftover grass seed you want to use to do it again, you have to make sure that grass seed is still good. If not, you won't be able to grow it. To check if grass seed is still good, put it in a cup of water for about 15 minutes. If the grass seed floats, it's probably not good and not going to sprout. If the grass seed sinks, it's still good and will probably sprout grass.