Ask Mr. Smarty Plants

We don't think we have enough information to adequately answer your question. For instance, how "fast-growing"? If the experiment is due next Wednesday, it's probably already too late. We don't know what level science you are working in: high school, graduate school, third grade? Finally, we don't know what principle you hope to prove from your experiment. There are, however, a number of Internet websites on science experiments with plants. We are going to look at several and list below the ones that might have the kind of information you need. Two plants we can think of that have seeds fairly readily available are radishes and dried pinto beans. You can buy small packets of radish seeds at garden stores. Buy a pound of dried pinto beans, soak several of them in a shallow bowl of water, in the light. They will sprout in a few days, and can be transplanted into small pots. Cook the rest of the beans with tomatoes, onions and a little ham. 

mgonline.com Plant experiments for kids 

sciencemadesimple.com Science projects about plants and botany

lessonplans.com What Happens When Seeds Sprout?