I forgot you asked how long can u keep them in the 18oz cup. That depends on how many transplants you will be making. Mine come out of the cup at 3 weeks, then into 3/4 gal pots for two weeks then into 2gal pots to flower. Sometimes the determining factor in how often one transplants their ladies is the size of the garden. I'm lazy at heart and only transplant twice. If your garden is small I'd transplant 3 times.