Hi Julia and Shaun
This leaf drop is not normal or desirable. It is most likely to be related to some sort of stress brought about by the planting process and/or practices after planting. There are many possible causes. Despite the best care and attention, roots sometimes get broken, the finer roots are quite brittle and often just the weight of the potting mix will pull off a section. If this happens then the root:shoot ratio is compromised and the remaining root system may be insufficient to support the whole canopy (especially if conditions are dry and hot) and a commensurate amount of the canopy should be pruned off to restore this ratio. Have another look at the video called ‘How to plant an avocado tree’, find it in the BPR under Library/Videos (or type ‘how to plant’ in the Search box). There have been cases where growers have put fertiliser in the hole at planting, this burns the roots which also results in less roots to support the top. There are other cases where growers overwater or underwater following planting. Salt in the soil or irrigation water can have the same effect but you would probably see some burn along leaf edges as well. Also depends on the condition of the trees at planting, were they progressively hardened off before planting or have they come straight out of a cool moist shade house into the harsh hot dry windy environment of the field? Did you inspect the root systems of a few trees to see if they were healthy and well developed? Most of these are covered in the video. Hope this helps. Regards, Simon Newett