Rhubarb can be eaten raw but because of its tartness, it is generally cooked and sweetened first. It can be sweetened with sugar, honey, syrup, or berry preserves. Because rhubarb varies in sweetness, it is hard to determine how much sugar is needed. The rhubarb will also sweeten as it cooks. Start out with a small amount of sugar. Once the rhubarb has cooked, more sugar can be added if necessary.