I was wonder what was wrong with my feijoa and these papers and the document from Montana State University Extension helped a lot. I have sandy soil, so it is pretty much devioid of nutrients. The solution is organic matter, but it takes time and money to compost. I’ve been supplementing with whatever I can figure out is lacking. Before it had yellow leaves and green veins, so that was lack of iron. Now it is the tips curly, turning brown and brittle. It seems to be a calcium deficiency. Blossom end root I had on my zuccini also is because lack of calcium. I bought lime to add to the soil, but I got to be careful not to increase pH too much or it could had it harder for plants to uptake nutrients. Slightly acidic is best. Wood ash also looks to be pretty good. Wood ash lacks nitrogen, but mixing it with a chemical nitrogen source is dangerous and release ammonia gas. Wood ash should be mixed with compost first.

I turned the two pages in the Montana State document into a single dot diagram.

Nutrient deficiency flow diagram