Can toothpaste lock hair

Depending on the toothpaste and what you want to grow I would say yes. If you would like to grow some bacteria and mold I think you could experiment with those organic toothpastes free of preservatives. Take this natural toothpaste and rub it in your hair and don't wash it for several weeks. I'll bet you a tube of Tom's of Maine toothpaste you'll get something to grow.