@Henderman thank you all for your replies. To answer your question: I got the property from previous owner and at that time trees had these signs of dead spots. Since the appearance is important for me i will probably replace these with new ones.
Currently, i do NOT use any specific fertilizers (suggestions are more than welcome), and started watering them once a week for the last month.
FYI, i am located in Ontario, Canada, and it sometimes gets -20 or -30C during winter. Do you have any suggestions for winter protection practices?
Thank you
Elvin