Wow, long time since I've posted here, busy with school. Now that spring has come around, and I'm watching my Opuntia humifusa's put on new growth, it got me wondering. What are some fast growing cacti that can tolerate freezing temperatures (since they stay in my sunroom it usually never goes below 20F in the winter)(i.e. I don't bring them inside over the winter)? I'm up for any kind of cacti - no succulents though. Thanks!