Hello, I have a site with 3 large Ficus maclellandii 'Amstel King'. They're currently dropping a decent amount of green, yellow, and brown leaves, one tree more than the others. I know this is common for them in the winter but the staff on site are under the impression that its quite a lot more than the previous years. They have not undergone any changes in temperature, light, or watering that I know of. They receive a daily 30 minute cycle soak of 10 minutes on, 10 minutes off, then 10 more minutes of water. We have checked and the irrigation is fully functional. I am thinking this may just be the normal winter occurrence, but I thought I would see if anybody else has any input. Since I have had this site they have been very happy and growing like crazy. As far as I know the soil has never been changed and they have not been fertilized. They are starting to outgrow the collar around the trunks so this may be adding some stress. See photos. Thanks!
Five things come to mind: 1. What's the humidity level in that place? Due to heating indoor air could easily turn too dry in the wintertime. 2. Does the sun shine directly at these trees through those ceiling windows in summertime? How the worst affected tree and least affected tree are positioned relatively to the sun exposure? If the exposure changes very much, because lower sun angle in the winter, then your plants could suffer. Plants construct their leaves according to the sun exposute. Shade leaves have different build than well lit leaves. Many plants react on extensive change of sun exposure with leaf dropping. 3. Even indoor trees may reduce their activity in the wintertime, therefore they could need less watering. If to continue your summertime watering habits, overwatering might happen, and figs have rather sensitive roots towards soggy soil. Constantly too moist soil can cause severe leaf drop. If too much fertilizerhas given, then that could cause salts to contcentrate in the soil and this reduces the rate how plants take water from the soil even more. 4. Many evergreen trees have natural tendency to renew their leaves in the winter, that can appear as moderate leaf dropping. 5. Pests problem, although unlikely in your case, could cause leaf drop.
The soil in container is also changing. If a container is watered 20 minutes each day, then fine soil particles are washed downwards pretty soon, so perched water table can be different this winter, than it was last year.
