Alternate Bearing of Mature Citrus Trees

Citrus fruit trees may become alternate bearing fruit trees for unknown reasons.  They may become alternate bearing fruit trees due to stress from drought, from a lack of trace minerals, or because of insects. Alternate bearing fruit trees may also be a way a tree controls insects.  By providing less food (fruit) in the lean years, insects cannot multiply as heavily; therefore, there will be fewer insects on the tree the following year when there is an abundance of fruit. 

During the lean years, alternate bearing trees have a leaf to fruit ratio that sometimes produces undesirable and non-typical fruit - misshapen, puffy, or dry inside. (This also can happen when a young tree first starts producing and usually corrects itself in sequent years.)  I have noticed that when citrus and other trees experience stress, they tend to produce more seeds which come in the form of fruit or nuts.  Trees that are root bound or trees that for some reason are in the process of dying will produce a lot of seeds.  This is kind of like, “I am not going to grow anymore, so maybe the only way for my kind to survive is in my seed.”  In fact, this is one way to get citrus to bear early - just let them become root bound in a pot.  But also the opposite can happen.  Taking a tree out of a root bound pot and putting it into the ground can cause a tree to stop producing fruit and to start growing instead.
 
In any case, when you have a healthy mature alternate bearing tree which is not stressed by insects, drought, or lack of trace elements, reward the tree when it is “loaded with fruit”.  Give it plenty of fertilizer while the fruit is developing, and conversely don’t reward it with fertilizer if it is experiencing a lean year.  In summary, cut out the fertilizer on the lean years and give the tree plenty of fertilizer on the “loaded” years.  Otherwise treat the tree the same during both a lean and a bountiful year.

Fairchild