Leaf Drop on Citrus

A few weeks ago, I gave our citrus bushes their first application of fertilizer for the season. I have read repeatedly how important it is to fertilize citrus with nitrogen especially in late winter to stimule them to grow and bloom in the spring. I have been using a 16-16-16 all-purpose chemical fertilizer on our citrus. We have two mature orange bushes (below picture), a very small page mandarin bush, and a small navel orange bush (picture above). A week after I applied the fertilizer, the mandarin and the small navel orange bush dropped many of their still green leaves. The picture above show the small navel orange after the leaf drop occurred.

I gave the small orange and mandarin about a cup of fertilizer each, which was probably too much. We had only a few light rain showers in the weeks after I fertilized, and I did not give them supplemental watering. Also, the weather has been cool with many cloudy days in the past few weeks, but we have not had any freezing weather. So I can rule out overwatering and weather conditions as possible causes. Last spring, our small orange lost even more of its leaves within a few weeks after I applied the same fertilizer.

Although leaf drop on citrus can occur for a variety of reasons, I am convinced at this point that the leaf drop has been occurring, because I have been applying too much fertilizer, which burned the roots. I have decided to start using an organic fertilizer on our citrus bushes and to use much less fertilizer, perhaps a third of a cup per application on our small bushes. I have read that organic fertilizer is less likely to burn the roots than chemical fertilizers, because the nutrients in them are much less concentrated. Our mandarin seemed to suffer the most after I gave it fertilizer. That’s strange because it had many yellowing leaves that were a clear sign of nitrogen deficiency. However, it is a very small bush (only about 18″ high), so it was probably more susceptible to root burn.

Our large mature orange bushes did not mind the chemical fertilizer. I gave them about 3-4 cups of fertilizer each. They lost very few leaves after I applied the fertilizer, which seems to confirm what I have been reading that mature trees can handle large doses of fertilizer much better than young trees. In the past few years after giving our 2 large orange bushes a few cups of all-purpose fertilizer in February, they responded by producing an abundance of blossoms and new dark green leaves the following spring.

March 07 2010 06:39 pm | Oranges