The Citrus Tree Switch : Sweet to Sour

Have you ever purchased an orange tree, harvested sweet oranges for many years, only to have a crop of sour fruit the next?  All commercially sold citrus trees are budded. A budded tree is like a grafted tree, except a single bud is used instead of a graft which is a few inches of stem containing several buds.  When you look at the trunk of a citrus tree, you should be able to observe a slight to obvious bulge. This is where the original budding took place; it is called the bud-union. Everything above that bulge or bud-union grew from that bud and is the variety of tree you purchased; everything below is of the original rootstock seedling. Sometimes shoots originating from below the bud-union will grow up into the tree. These are typically covered with large thorns. If the shoots not pruned out, they will continue to grow, branch and eventually form a good part of the tree. Rootstock branches are usually more vigorous and will eventually blossom and produce fruit. This fruit is different from the variety you originally purchased, and most often is quite sour. These branches must be cut out so the original budded variety can repopulate the tree and produce sweet fruit.