I am a first time gardener and am learning as I go. I have tried to figure out when watermelons are supposed to flower. I planted 6 hills of black diamond watermelon seeds in March and so far, we have about half of them doing relatively well. Each plant is about 5-6" tall (and growing) and the leaves look healthy and green... but no flowers. When are they supposed to show up? I've tried looking it up, but I haven't been successful. Any ideas? Thanks!