My guess is that you useorganic fertilizer, heaped on the soil.
this year im trying something new. its Gro-Power tablets 12-8-8 NPK, 20% Humus, 4% Humic Acids, 3.5% Sulfur, 2% Iron, Micronutrients. I placed them in fertilizing baskets. but i seem to have always had this problem is why i switched to this fertilizer.