Q: I have an orange tree that used to produce sweet fruit. We pruned it back a few years ago after a freeze and now it only produces small sour oranges that are full of seeds. Is there some kind of fertilizer we can apply to the tree to make it produce the sweet oranges again?
A: I get this question often especially during the spring after a cold winter. I am afraid I have some bad news for you; there is no fertilizer you can add to the ground to make the sour oranges sweet. I suspect your original orange died as a result of the freeze and the root stock, which is probably a sour orange, is the only living portion of your citrus tree. Sour orange is a common root stock because it is so cold hardy, but as you noticed the fruit is inedible. Once the scion, the grafted portion, dies the hardy root stock will totally take over the tree. On citrus trees, be sure to protect the area where the scion and the root stock join in order for the upper scion portion to survive freezing temperatures. Even if the top portion freezes, the tree may be able to recover once temperatures become warm again. You have several options: graft another sweet orange back onto the sour orange root stock, dig up the tree and replace it, or leave the tree and enjoy it for its beauty.