The switch from traditional pots to ‘airpots’ (pots full of holes) is a recent development in arboriculture. Not without reason: tests have shown that the root development in airpots is better, with a balanced root system as a result. Especially when growing Eucalyptus species, it is important that root formation goes equally well in all directions. In the old-fashioned way (in closed pots with only drainage holes at the bottom) roots rotate in the pot, forming a spiral root ball. If such a tree is planted, it will not recover. As a result: after a few years the tree will have grown large, but with an asymmetrical root system. Such a tree often blows over in a violent storm. For a long time, it was therefore advised to plant only young seedlings, so that a balanced root system could form.
It took me quite a few Eucalyptus trees until the penny dropped. And lately the penny has dropped with more and more tree growers!
From now on it will be possible to offer increasingly larger trees, without the risk of them being blown over. There is a great need for this!
As soon as roots grow out of a hole, their growth stops. This requires the plant to make new roots in the root ball. Roots no longer rotate in the pot! An additional advantage is that the tree is more compact grows and forms a firmer trunk. But unfortunately, airpots are more expensive than regular pots and cultivation in airpots requires more water.
According to a study at a nursery in Oirschot, the improvement is in the thickness increase of the trunk as much as 26 to 61% – depending on the tree species – compared to the traditional method in open ground.
See: https://www.boom-in-business.nl/article/32232/met-de-juiste-aanpak-werpt-air-pot-zijn-vruchten-af (in Dutch)
(we use a slightly different type of airpot as the one described in this article,but the operation is the same)