My pistachio had been in a red solo cup and doing just fine. I'm not sure how fast pistachio's grow but this one was unchanged for months. So I decided to pot it up. The roots on it were starting to curl at the bottom of the cup but not too badly. It did have an amazing root structure. I have moved every single plant I own outside because of a massive bug problem I've been experiencing. Buyer beware when bringing plants into your house. I had some bugs come with plants I'd ordered on Ebay and they were expanding quicker than I could control them. I even went against my principles and use a major insectiside on all of my plants. Anyway, so they're all outside, the bug problem is being dealt with naturally and the pistachio appears to be improving and flourishing in it's new environment, sans bugs.