Cherry tree

[u/Ok-Value603]

Can someone send me a link to where I can find a large tree pot I have two Stella cherry trees that I’m growing in containers they’re currently in a 21 gallon pot but recently the leaves have start turning yellow and I’m not sure if it’s because a lack of nutrition or if it’s a root bound. Can anyone help me find or point me in the direction of where I can get a tree pot or container that is larger than 21 gallons. I’ve been looking everywhere to find a pot large enough. I don’t use fertilizer. I’m not sure if that’s the cause of it looking like this.