If seedlings are allowed to continue growing in their pots for too long root binding will occur. This happens when growing, elongating roots meet the walls of their container and cannot grow out or down any further. The roots then grow along the sides of the pot creating a mass of intertwined roots. This impairs the plant’s ability to absorb nutrients and water and can eventually lead to ‘root strangling’ where the root collar will not be able to thicken and support the above-ground parts (see Figures 1 and 2). One result of this constriction can be delayed or stunted growth and is particularly problematic for trees, creating a weak point at the stem base. The tree will break at this point, sometimes many years after planting (see Figures 1 and 2).
Example: One of our growing Pinus halepensis pines reached a height of 20 m with stem diameter (dbh) of 60-80 cm. The tree fell on a clear day with no wind. Examination of the trunk base revealed that it was "choked" by restricting roots to a diameter of only 20 cm! This was not enough to support the tree hence its collapse (See Figures 1 and2).
Solutions:
One. With plants grown from cuttings the problem can be overcome by planting in a relatively deep hole (compared to the orginal growth pot) so that the plant will be able to develop a new root system with less constriction.
Two. Each pot plant must be examined prior to planting to see if there is a problem of root curling. If there is, cut away the curly roots before planting. Care should be taken here so that the plant top is not too large relative to the remaining roots.
Three. Use JNF recommended ‘Quick – Pots’. These are partially open-bottomed and have the advantages of allowing the roots to grow directly downwards where they are air-pruned. The remaining root mass will create a good root-soil contact when planted out.
Figure 4 JNF ‘Quick-Pot’. Note the roots have grown straight out of the pot bottom and have been air-pruned.Figure 3. Severe root curling due to overgrowth in pot.Figure 2. Example of a root that has strangled the trunk base.Figure 1. Eucalyptus spathulata: tree fall attributed to root strangling.
