Gerenium upper leaves getting yellow

[Muhammad Bilal]

Assalam o alekum

My Geranium plant kept in semi shade and getting sun till 11am, getting his upper leaves yellow, while lower leaves are normal, can seen in pic below. My little knowledge says it is due to heat effect as day temp: here is 35 and night at 20 centigrade.
It is not the Iron nor another mineral deficiency as I feed them regularly in active growing period. they are in well drain porous soil and I m too careful in watering as well.
Want to know the actual causes of it , Need ur valuable opinion on it plz and thanks in anticipation

[Izhar]

soil borne fungus and high pH could be the cause..

[Syed Adnan]

I have grown this lovely plant a lot and I have noticed an overwatering could result into yellow leaves and finally stem rot, where the whole plant can fell off in hours and dead. Be careful with over watering , it is drought tolerant plant so let it be ... .