Agree patience is key. Once java moss gets really going, you'll be pulling out gobs of it to keep it the size you want. I made a moss ball by using the flexible plastic netting that us often used to package foods. I put the moss inside (loose, you want good water flow), and let it grow out the holes. I move it around to new tanks after resets to help seed good bacteria and act as an extra biofilter while things establish, and another lives in my fry tank to provide a surface for infusoria grazing.