Ginkgo biloba are a fascinating species of tree and everyone should have at least one in their bonsai or tree collection. Recently I have been experimenting with defoliation techniques on them to aid with encouraging back budding and improve the density of buds on the branches which in turn will lead then to smaller leaves as there are more of them to aid with supporting the root system. Here are the results so far.
Prior to defoliating any species of tree, ensure that it is healthy and growing vigorously as this will aid with the production of a second flush of leaves.
Defoliation is a good technique to use to aid with ramification and it can also aid with foliage coloration in the autumn too which for Ginkgo is a benefit due to the fabulous yellow autumn colour they have.
You can vary the amount of foliage defoliation, so you do not have to remove all the leaves, if you want to improve one area of the canopy, one method is to defoliate the more vigorous areas whilst leaving the weaker areas to develop further. This allows more light into the canopy of the tree too and promotes buds that were dormant to flush.
The watering requirement of the tree post defoliation is reduced but I have continued to maintain a light liquid feed in the watering to make up for the loss of the leaves to ensure the roots have a source of nutrient to reduce the stress on the tree and it using its stored reserves.
This is a stressful process for trees, therefore they should not be exposed to additional stressful conditions and semi shade position seems to be working well at present in addition to moderate watering and light feeding.
The majority were defoliated in mid May to early June and the new buds are developing well. The first one to be defoliated was a small twisted shaped bonsai and I left one set of leaves on for comparison of leaf size when the new leaves form and the new leaves are significantly smaller than the original leaves.
During the defoliation process I left some longer leaf stalks or petioles as the Ginkgo produces new buds from within the centre of the leaf stalks. Also I have tried to reduce the water loss on the cut leaf stalk ends by misting or spraying initially post defoliation as some of the leave stalk ends have died back slightly as they have dried out but they are starting to re-shoot with new buds now.
In terms of time scales, the full canopy of leaves should form within 4-5 weeks of defoliation and so far this is proving to be correct with the ones I have defoliated. It has also been a good opportunity to remove any unwanted shoots, reduce down the size of shoots and re-structure the shapes lightly to improve the overall form or style.
So currently happy with the progress, but I won’t probably carry out defoliation again within this year as our summer season is not sufficient to allow for a 3rd flush of leaves and this would potentially be too stressful on the trees in this climate. I may try defoliation every two years as opposed to annually but will await the results of this trial first.