Type of mango tree you have might help answer your question. I am new to planting mango tress, well not entirely new I planted a Home Depot Manilla in the ground couple years ago and neglected it. But it grew strong and big with just sprinkler water without any fertilizer and fruited every year. I now have 12 varieties of mango trees, planted 9 in the ground and planning to grow rest condo mangoes (Ice Cream, Pickering and Cogshall) in 65 gallon pots.