Heat inside the bonsai pot
There was a post at IBC where Andy Walsh is a frequent contributor, then was asked to direct sunlight shining in black plastic pots for training could warm up enough to damage the roots. In typical fashion, he responded with a more complete and well researched.
Trees on the ground
High temperatures can seriously damage the roots of plants growing in pots.
As everyone knows, the roots of trees in nature usually experience a certain amount of temperature variation. On the ground the roots of power tend to inhabit the trees safer few inches in depth the effects of the heat of direct sunlight and warm air from the surface and the deeper, the danger is canceled.
It is obvious that some of the roots of trees can feel very high temperatures in nature, however, a forest or a clump of trees with little incidence of the sun on the ground, the roots have milder temperatures and more constant. This is probably true for the more wooded areas, as well as my backyard. (I’m sure we’re all aware of how the soil is cooler when sitting in the shade of a tree).
Trees in pots
In the world of culture vessels, the situation is somewhat different, large temperature variations as described above, may be much exaggerated. In most cases, the roots are just on the inner surface of blood vessels and can be quickly and easily affected by direct sunlight and air temperatures.
As is often the bonsai are arranged on shelves and are not closely arranged providing continuous coverage of vegetation for shade containers, such as nurseries that usually arrange plants in plots to maximize space, bonsai however, are usually too spaced to ensure that all areas get sun and ventilation, so the roots of trees grown as bonsai usually have higher temperatures.