I believe that producing issue is either the sterile pollen problem mentioned in the article, or just lack of properly feeding the plant. I discussed in email with you about a McDill growing north of here that is quite tall but produces few, mediocre fruit. Meanwhile, another one 15 miles away in the same soils and weather environs produces heavenly fruit - and in such volume that 1/2 of it is thrown out. Now the latter tree is getting feed about 2/3 cup of Gro-Power 8-6-8 every month. But the mediocre fruit is coming from a large tree that gets watered well but only a pitch fork or two of composted horse manure per year. Composted horse manure can be a fabulous fertilizer but not in that volume. It has an N-P-K of around 0.7-0.3-0.5. You need a 3.5 cubic feet of it per year for a tree 8 feet high and 8 feet wide and the tree in question probably needs double that.
Robert Chambers is correct about White Sapote producing the most carbohydrates per square foot of any plant. A tree in the front yard of an estate in Poway CA rains fruit every month on the owner. What I've read in the USDA reports is that on average the white sapote is tied for 1st place with a legume field crop and something else I've forgotten. It's an incredible output. The Suebelle cultivar produces less than average and a smaller fruit, while some like the McDill are famous for raining ankle-deep fruit year round in zones 10 and up.
The article I'm working on will be published in a horticulture magazine, but it will also be online. You can view the first two pages here and I'll strike up the band when I've finished -- hopefully by March: http://www.plantsthatproduce.com/col..._06_Sapote.pdf
Now you can call me Bob, or you can call me ... But actually I'm Richard !
Robert Frost is my father, the rocket scientist. Jack Frost is my uncle's cousin who lives in Mentone CA. Howard Frost is our relative that bred all the citrus varieties at the Riverside Ag station. That other Robert Frost guy is a black sheep of the family that moved to the Midwest and wrote poetry.
And here's the White Sapote in my front yard that I'd be delighted to have rain fruit!