DateTime Conversion Persist

I have the following code which is giving a persisted MM/dd/yyyy although I specify that I want it in dd/MM/yyyy. What's wrong?
 
                string dtDtDates = Convert.ToDateTime(dtDates.Rows[i]["fldDocDate"].ToString()).ToString("dd/MM/yyyy");
                DateTime validDate = Convert.ToDateTime(dtDtDates);  // result =  05/10/2011 (10th May 2011)
                // These values fetched from DateTimePicker
                string dtDateFrom = dateFrom.ToString("dd/MM/yyyy");
                DateTime dtF = Convert.ToDateTime(dtDateFrom); // result =  ...