Are Grow Bags a new technology?

No. Grow bags have been in use for over 40 years, developed by Dr. Carl Whitcomb, University of Oklahoma
-  He has written several books on nursery production and growing trees in grow bags
-  His company, Rootmaker, makes grow bags.  Another manufacturer is High Caliper.  We use both brands of bags at Amherst Nurseries.

How do Grow Bags work?
-  The bag is designed to allow small roots to penetrate the bag, rather than hitting the wall and turning to circle as in a plastic container.
-  Root penetration through the bag also allows the root access to nutrients and moisture outside the confines of the bag wall.
-  As the root grows and enlarges, the bag constricts the root, effectively pruning it at the wall of the bag.  As the root enlarges in the bag, a node is formed against the wall of the bag, providing a reserve of carbohydrates for the plant that can be utilized once the bag is removed at transplanting.  In this way, the root system retains as much energy as possible, rather than having it severed as it would be at B&B harvest.

How does the plant establish itself?
-  Each root node that establishes at the wall of the grow bag produces 5-20 lateral roots once the bag is removed and the tree is planted.  
-  These roots will be in the top 12 inches of soil which is exactly where the roots need to be, mimicking how trees grow in nature.
-  Overall establishment is rapid and strong root systems are the net result.