30 gallon of 55 gallon barrel will have 4 handles for four people to carry.

Mixes 5-1-1 Mix -- 5 parts Pine fines, 1 part peril light, 1 part peat moss or equivalent Equals one light mix plus one very happy tree.

If you're growing long term in a pot you should root prune regardless of how often you increase the pot size. Basically if you don't prune, the roots get progressively thicker and woody reducing the overall percentage of feeder roots. I didn't want to buy/lug a larger pot for my lemon tree this year and decided to root prune for the first time. It was easy and the tree is doing great.

Here's an old post I found on the container plant forum that explains root pruning better than I ever could. It's not specifically geared toward citrus, but I found it helpful.

Here is a link that might be useful: Root Pruning Trees

Thank you to those who responded. This was very helpful to me.