There are many factors, so it's hard to say. Weather is also a factor in that if you get a warm spring and a cold snap, it could freeze buds causing them to fail. That happened to many of us in North America this year. Several factors affect fruiting: Weather Light Pollination Water Nutrients pH Pests/Disease Alternate year bearing (from fruiting too much in the previous year) Maturity (some fruit plants take many years to fully bear) Pruning Some of these factors you can control, some you can't. Best to optimize the factors you can control, and pay attention to those you can't (such as weather). Research each variety and determine what they need and give it to them. Learn to prune correctly. Learn IPM (integrated pest management. Fruit trees are more difficult then many other plants to grow and maintain correctly. You'll have to arm yourself with knowledge of each tree and conditions. Fruit tree maintenance changes from year to year as well as they have different requirements as they mature, and each year seems different as far as weather, pests, disease and pollinators. They are about as high maintenance as you can get, so it's always ongoing learning. Good luck.

"See if you can find any information about P that is actually based on research in the field where a lack of it has caused production problems. Check into Australian fruit production because, as I recall, their soil is ancient and very low in P." I Googled for a little bit and really didn't come up w/ much scientific info. (At least they didn't explain any science behind it.) I quickly came across a few examples like this: http://archive.agric.wa.gov.au/objtwr/imported_assets/content/pw/gard/nutritional_gn_formatted.pdf where they have a quick blurb about P, where they say, "Phosphorus is essential for the development of flowers, fruit and roots....In fruit trees, flowering and fruiting may be affected. Deficiency symptoms are more prevalent during cold, wet conditions. To correct the deficiency apply solid or liquid phosphate fertilisers." Ive read lots of stuff like this in the past, but I know you are looking for something more substantial. In Prof. D. Layne's book "The Peach, Botany Production and Uses", he mentions that P is rare in peaches and that generally there is no response to adding it. Interestingly he does say that P deficiency can occur, causing reduced growth, without any visual symptoms in the foliage. I'd post the link to the book, but since it's a copyrighted book, the link may not pull up the same pages I was reading. Google books does that sometimes. I know you are somewhat annoyed that commercial guidelines could recommend adding P w/o a soil test, but again it's only for the first two years, it's a small amount, and in a commercial orchard, where that amount of P would probably be used up by the time it got down to the root zone. The U.C. Davis link you posted above get their info. from their nutrition manual (linked at the bottom of their page). The authors of it even state, " In fact, annual requirements of fruit trees in general range from 5 to 10 lb/acre (6 to 11 kg/ha), which is much lower than for many field crops." Although they don't specifically state a maintenance program for P is required, they do imply it. Of course they don't recommend application of nutrients w/o testing, but U of GA only mentioned it for the first two years, which isn't a big issue to me. I've always read that P is very stable and immobile in soil, so I think the risk of pollution from a couple very light applications of P is very minimal. It seems most pollution from P comes from sewage treatment and feed lots. The link from the U.C. Davis nutrition manual says,"However, there is minimal leaching loss of phosphorus from the soil because it exists predominately in these insoluble forms." To me the danger of too much P is the reduced uptake of Zn, which is pretty important to peach trees. But there is little risk of too much P in this area, unless someone was careless w/ applying it. You may be right, that P doesn't matter for fruit trees, but there seems to enough university publications recommending a minimum level for it, that I think it warrants addressing in soils low in P, such as in this locale. Although I agree, there does seem to be a degree of conflicting advice about it. I think Rayrose has a very good point that Ph is just as important as the actual level of P in the soil, in terms of root uptake. I also agree that too much emphasis should not be placed on any one nutrient. I hope I haven't left the impression that P is the only nutrient that matters, or even the main nutrient. I just originally addressed Clark's situation based on my own soils, which showed P the most deficient of all nutrients. But I tried to qualify that by recognizing soils my be different in his part of the state.

There are certain chemicals that can be expensively applied - Dipel or Florel IIRC, IMHO not worth the cost. We used to do it in California for olive trees and it was a nasty affair on 20' trees. Can't imagine what a 50-footer would do. And what resin said about the food source... Dan

You may be more likely to get an answer in the "Florida Gardening" forum, Jacaranda won't grow in most areas of the country.