Why do fruit trees have dark green leaves but bear little or no fruit,
especially if they are well fertilized?
Here is a brief lesson in plant nutrition: in general, nitrogen is for
vegetative growth. Consequently, when fertilizing a lawn or any plant grown primarily
for its leafy growth, the main nutrient to apply is nitrogen. When growing
plants for fruit or flower production, as opposed to foliage, a balanced
complement of phosphate and potassium needs to be applied along with the
nitrogen. Applying large quantities of a
high nitrogen fertilizer to fruiting trees like citrus and avocado will put
them in a ‘foliar growth mode’, producing an abundance of dark green leaves but
little or no fruit. Be careful how much high nitrogen fertilizer you
apply to the plant.
Urea fertilizer contains 46% nitrogen, ammonium sulfate 21%, while manures
in general contain less than 5% nitrogen, usually around 2%. For more precise
instructions on fertilizing fruit trees, CTAHR has a short publication titled Fertilizers
for Fruit Trees in the Home Garden #37. It can be accessed online or at UH
CTAHR Office at 875 Komohana St, Hilo, Hawaii. Other state extension offices in the U.S will have
similar publications.
