It's amazing what a root system will tolerate if you bare root, prune roots hard, and don't allow the roots to dry out while their being worked on. Examples:
Ficus benjamina
From this:
To this:
Boxwood
From this:
To this:
Acer palmatum (Japanese maple)
From this:
To this:
Every spring, I habitually repot some 150 trees that are suffering from the limitations imposed by root congestion/ being rootbound. It's only by repotting and root pruning that the grower can entirely restore the plant to a state in which it is not losing potential due to root congestion. Potting up, even if you trim the roots around the entire perimeter of the root mass (except the top, of course), still leaves the congestion in the center of the root mass as a limiting factor, and only allows the tree to throw off a fraction of the limitations imposed by root congestion.
When you pot a plant up and you see what you determine to be a "growth spurt" ..... it's not a growth spurt at all - just the plant returning a little closer to how it could have been growing all along if not for being rootbound. The limitations begin about the point in time where the root/soil mass has fused into a unit that can be lifted from the pot intact. All 3 examples above were being seriously limited by root congestion. The repot with root pruning eliminated that congestion entirely, not partially, as potting up does.
While it's not necessary to go as far as I did for plants being planted out, something close to that but not quite as severe is appropriate for most woody material that will be grown long term in a pot.
Al
