Thanks Princy , I handled it by using shared calender and set min date by client side ,
i have other issue , i have the same (2 date picker start and end date) in rad grid in edit mode each date picker in deferent column .
my problem is how to find date picker in client side in rad grid in edit mode by using this way ($find ('<%=rdpenddate.ClientID%>')) to set min date
or is there a way to pass extra paramater to client side datepicker function from code behind for example
//set min date code