Felt bag for woody plants

I came across the process of "air-pruning" when studying nursery operations some years ago. Plants roots has several enemies, which includes air and copper, and when they are encountered, the roots would die. This process is utlilised mostly by the nursery industry to prevent girdling and encourage the formation of root tips (at the periphery of pots) in woody saplings and container trees. The additional benefits include improved drainage and aeration, leading to less heat build up than in plastic and clay pots. I encountered the air-pruning containers again, in the form of felt bags in a tree nursery. But the felt bags were not used in a correct manner, as pictured below.

Tree nursery with a batch of Aleurites moluccana.

The felt bag was buried resulting in a reduced contact with air, but fortunately, the bag managed to hold most of the roots in.

In order for the air-pruning containers to work well (whether they are felt bags or containers with holes at the sides), they should be in full contact with air, as root tips would desiccate and die when they meet air. I chanced upon some inexpensive felt bags from an overseas shopping website and order two to try out. The website made shoppers to buy in twos, presumably to make the most out of the postage. The following photos shows the repotting steps for woody plants that are to be kept indefinitely as houseplants.

Not the photo of the exact product, but its just a seemingly plain bag.

The inside of the bag facing noon-sunlight.

 The plastic bag that the plant came in had its bottom cut out and it was inserted into the felt bag.

 The remaining plastic bag was pulled out, and additional soil could be added for a snug fit between the root ball and felt bag. After the roots are established in the felt bag, it is not recommended to move it by the handles, as the roots at the periphery of the bag would break. Thus, a pot tray should be placed below the felt bag.

 Syzygium polyanthum are grown for their leaves that could be used in cooking and fruits that attract birds.

Coccoloba uvifera are usually found along the coasts in the tropics. Their fruit are edible but are cultivated mostly as ornamental and windbreaks.