As a rule, pruning will start in the second or third winter, depending on the tree’s development. The holm oak usually forms two or three dominant trunks, which it is better to cut from the beginning when they are young and still small in diameter. Pruning has traditionally been carried out at the end of winter, but in climates where trees grow too fast we recommend green pruning in summer, because pruning at this time limits the tree’s vegetative growth.
Last week I was in north Spain analyzing truffieres. One of them you can see in the pictures. It is an orchard of 9 years old that is heavily pruned each winter to turn again to the same size, so not allowing these ilex to grow higher. You can see at the second picture a control tree not pruned. Level of truffle infection is great, and some trees already producing. It will be nice to see how yields develop this way.
Note that holm oak leaves can stay in the tree for over 3 years, but the old leaves just breathe and waste sugars produced by the new leaves, so competing with truffles for nutrients. It is advisable to prune trees inside the canopy, so that this is aerated and permits rain to pass through it and wet the soil. Otherwise, the holm oak tends to form an umbrella and gather rain water at the base of its trunk as a funnel.
It is now known that the truffle extracts all its carbon and sugars from the tree, which is why it is necessary to maintain a tree healthy and vigorous. No heavy pruning should be carried out that curbs the tree’s development or significantly impairs its photosynthetic capacity. Therefore, heavy or green pruning should be carried out, above all, during the early years, before entry into production. Once production begins, pruning should only be done at the end of the truffle gathering season (end of winter), to generate new shoots and new leaves with a higher photosynthetic rate.
Watch out for cankers like the ones on this pic, mostly caused by phytoplasms. Disinfect pruning tools in order to not propagate them.
Note I will be in California (USA) in mid june analyzing some truffle plantations. As I still have not closed the schedule of visits, if any grower in the area is interested in a technical visit, just write me at firstname.lastname@example.org
Marcos S. Morcillo