The notes on the recipe said:
If fresh rhubarb isn't available, make it with frozen rhubarb, thawed and well drained. The cake is good either way, although it's moister and more pudding-like with fresh.
The original recipe called for mixing 2/3 cup sugar with the rhubarb, but I cut that in half because I believe you should be able to taste the tartness of the rhubarb. I love the burst of tart flavor from the rhubarb balanced against the sweetness of the cake. I hate that most recipes want to hide that tartness with so much sugar! If you're looking for sweet, then I think you should try something else, because rhubarb is tart, and that's what makes it special!