Although it's a hassle to prepare unless you live in barbeque country, some FINE nutes are made with fruit and vegetable rind ashes. Cantaloupe rind, banana peel, and corn cob ashes have absolutely great quantities of potassium and phosphorus, which are the two more difficult to find nutrients in free ferts. I used to have the chart of which has what, but i lost it and seeing this just posted without trying to look it up; if you're serious, you'll be able to figure out how to get the chart off the net... but i grew a fantastic crop of weed using almost nothing but fruit & vegetable ashes. One good thing about the ashes of various rinds, is they also have a good spread of lesser micronutrients. The plants i grew with ashes never had deficiencies, and if i had to do it again i'd absolutely have no fear whatever there was going to be a problem. I did use a TDS meter and i had to acidify the water but it's absolutely a much overlooked source of fantastic nutrition.
One thing i found very telling was that for most of the crop i was able to feed the plants on nothing but burnt apple and banana peels: something the charts say are short of some nutrition: but the plants grew like amazons and were absolutely covered in trichs, and potent as anything i've grown in those strains.
I'm not a bbq kind of guy so preparing mine was done on a heavy metal mesh screen on the inside gas stove, with the evacuation fan on. I did it at night and still at times the house filled with smoke and that made it a hassle but if you have a bbq pit and can ash them like that, it'd be totally fine, and i'd do it again in a flash. One cool thing about doing it that way is that a lot of us pot heads don't exactly eat all our fruits and veggies; eating the apples and bananas, ( i threw the fruits into the blender and made smoothies) as well as the cantaloupe and corn-on-the-cob did enhance my diet during those months i did it.