Q. My peach tree sometimes produces peaches that split up the sides. What am I doing wrong?
A. I had to go looking. Here is what i found from Washington State University. It is a bit technical so I inserted some explanations about what they are talking about.
Peach splitting can show up as split-pits and as split fruit with the pits still intact. Split-pits are the more common problem but our understanding of this phenomenon is still limited.
We know that split-pits can occur about 20 days after bloom or during pit hardening. Early season peach varieties, such as Early Haven, usually show the problem more often but later season varieties can also have split-pits. Rainfall is not responsible but may aggravate split-pits. There’s been no consistent association between micro nutrient status deficiency or excess, in trees and split-pits.
It appears that anything that upsets the carbohydrate balance between leaves and roots can increase the split-pit problem. This includes winter injury, girdling, high heat, heavy watering, excess vigor, or trunk damage. The relationship between growth rate and split-pits is very close.
Much of the split-pit tendency is a cultivar of variety characteristic that is genetic. Gardener control, other than choosing varieties that have less tendency towards split-pits is, limited. Controlling tree vigor may reduce the problem. Don’t excessively thin or over-fertilize. Unfortunately, these practices will probably give you smaller fruit size.
The other splitting problem in peach is in the fruit itself, called soft suture. It can sometimes be traced back to a fluoride toxicity reaction or a response to one of the growth regulator chemicals like 2,4-d. We suspect soil moisture may be a factor. Some varieties tend to be more prone to soft suture symptoms. Symptoms are similar but the fluoride toxicity symptom shows red pigmentation under the skin, the growth regulator response does not. In addition, the fluoride related response usually is on the lower 1/3 of the suture, near the calyx end.
In the case of fluoride toxicity, spray applications of calcium chloride every ten days beginning about two weeks after pit hardening have been effective.