Last week I dug up one of the Oaks that I was growing in a very large pot and had a good look at what was happening underground. I was becoming a little concerned about the type of roots developing and feared deep thick roots and growth up against the side of the pot.
I was really surprised at the quality of the roots that came out. A nice dense root ball with very few thicker roots. Clean and healthy too with no dead roots or an smell at all. There were plenty of choice surface roots to work with later as well.
I trimmed them back and decreased the depth of the root mass to make it easier to pot later. As I reduced the depth of the root ball I came across no thick deep roots that were going to be a problem later. Its gone into a large air pot now for finishing off over the next 2 years.
So its maybe not as effective as field growing - but for now it easier to manage and gives very good roots. A lot easier to lift from the big pot and retain quality roots that digging up too. I will definitely continue to grow Oaks like this.