...and I wanted to ask - How often would one use 0-0-50 in a season?
Just once after fruits are through and that's it?
After harvest is what people say but Fairchild says 3 times a year which is probably better. Potassium will not burn so you cannot overdo it like nitrogen. Not that you want to waste it.http://www.fairchildgarden.org/livingcollections/tropicalfruitprogram/jackfruit/growing-a-mango-tree/
Ten Easy Steps to the Perfect Home Garden Mango
1. Choose a healthy tree: A 2-gal container is a good size. A small tree will establish quicker and grow better roots to resist hurricanes.
2. Planting the tree: Select an area where the tree gets sufficient sunlight for good production.
3. Water the tree until established – 1 to 3 months. Do not irrigate after establishment – as irrigation will increase disease and lower fruit quality. (Mangofang and other desert denizens need to irrigate)
4. Fertilize lightly with low analysis fertilizers. We recommend that no nitrogen fertilizers be applied. (I disagree. Use good NPK fertilizer with minors on young trees. Once they really get fruiting then just potassium unless you want a larger tree. Fairchild promotes the philosophy of smaller bushy trees)
Fertilize when your tree is active. Do not fertilize during the winter time. We use a 0-0-50 formulation, sprinkled lightly below the drip-line of the canopy three times per year. Fertilize 3 times per year with foliar micronutrients that include magnesium, zinc, and manganese.
5. Tipping: Begin tipping in the first year and continue for the life of the tree. Trees should be tipped every 20 inches. (20 inches folks!!!)
(more at link)