...if you can bury them in the soil or build a wire frame for each I think they're great.
Not really, when the roots hit the fabric edges they divide. It's a similar system to what Chris uses at telperion farms. Eventually a tap root may escape the bag but the majority of the root system remains contained.
... they lift the trees and prune any escaped roots at least annually...
So what is the point of the collander? Why not just plant your tree on a mound and just use a sharp shovel to root prune however often you wish?
I can imagine that there might be one benefit, that being that the root/soil mass inside the colander won't "fall apart" when lifted...which can happen with the technique you describe.
Thanks for your response. I'm just asking. My sniping isn't directed at you. It sounds to me that there is a 'sacred collander' religious sect forming. Don't be so open minded that your brain falls out.
The point of collanders is air pruning roots and possibly drainage - exactly the same principle as Vance's patent - which is defeated by burying the collander or Anderson flat or pond basket or the like. Burying them is just plain silly and unlike Brent Walston's 'great escape' accident/method.
To this point of simple root pruning, 'lifting' is not implied - just leave it in the ground - stick the shovel in the ground to cut the roots around the trunk and move on (optionally, remove the roots outside the cuts). Planting on a mound just makes it easier to slice the roots underneath.
No they don't. If you get one root to escape you have a full scale break out. In two years if it is not corrected that one root replaces the entire root system you have been trying to develop in the colander. You may still have roots in the colander but the shock of removing the new dominant root and it's ancillary root system will take two years to recover from.
I don't know, I never got a good answer...just reporting what "they" said. I repeatedly asked what the root systems inside the colander looked like when treated this way, again...no real good answer.
Edit to add...I can imagine that there might be one benefit, that being that the root/soil mass inside the colander won't "fall apart" when lifted...which can happen with the technique you describe.
Sorry I have to disagree with you on this one thing. I was at Telperion farms last fall and dug up a number of trees with him. In about half the cases of the 6 or 7 we dug a tap root had escaped the bags on the bottom, he just chopped it off in all cases. The root system and nebari within the bags was fabulous and I was able to bare root all of the trees we dug the following spring. Perhaps his bags are a different material but they look the same? He posts on here from time to time maybe he'll see this thread and respond. I haven't bought healthier field grown trees from anyone. He does not grow straight in the ground all his trees are in root control bags in the ground.
About halfway down this page you can see a picture of a satsuki in a root control bag. http://www.telfarms.com/trees/about
I researched grow bags at one time and noted some grow bags are lined with a copper substance that is poison to roots. I think Root bags get buried in nurseries for practical reasons; moisture and stability.