Magnesium sprays can improve the retention of fruits onto the tree, reducing fruit drop. Common practice is to use foliar applications at petal-fall, fruit set and then at 10-14 day intervals to help overcome any set back in growth (e.g. due to low temperatures) or fruit loss from the tree. Soil Mg applications ensure regular long-term supplies are available within the tree.
Whereas the effect of nitrogen on the number of fruits per tree is not clear, particularly phosphorus and magnesium have been found to increase fruit number.
Boron, iron and zinc also support higher yields by helping the tree to produce more fruits.
Crop Nutrition and Stone Fruit Number
While phosphorus is not needed in large amounts by the trees, on phosphorus deficient soils it can have a direct effect on the number of flower buds and fruit set.
The key benefit from boron is at bud burst and flowering when it is used to maximize fruit set. Trials confirm that best results come from applying boron in the autumn two to three weeks before leaf-fall targeting the foliage and buds. This boron is then more available to encourage better flowering and fruit set in the following spring.
Similar to boron, a poor zinc supply results in flower abortion and fruit loss. Early spring sprays while leaves are still expanding are the most effective in achieving the desired higher zinc levels in leaves.