The experts at the University of Arizona College Cooperative Extension have a useful guide to fertilizing citrus and it updates the timing of when to feed some citrus plants.
Lemons and limes stay close to the schedule we’re all familiar with: February, April, and September.
Oranges, grapefruit and tangerines shift to a February, April, June schedule. That’s a big change.
Here’s a link to the Citrus Fertilization Chart. It’s easy to read and figure out how much fertilizer your trees will need.
It is best to use a fertilizer formulated especially for citrus or generally for fruit and nut trees. All citrus trees will benefit from a heavy nitrogen fertilizer that has some phosphorous in it. Citrus trees also like to have somewhat acidic soil, so look for that in a fertilizer, too.
We like the organic Jobe’s Organics Fruit & Citrus granular, a 3-5-5 fertilizer that will gradually provide a safe, long-lasting food supply to your citrus. It also contains a proprietary blend of beneficial microbes that help growth.
Read the instructions on the bag to determine how much fertilizer to use, depending on the size of your tree. We find that the best way to apply to established trees is to scratch up the soil to a depth of 4 to 6 inches around the dripline of the tree. Put the fertilizer in the trench and water it in slowly. Very slowly, even over 10 to 12 hours. What you’re going for is slow, deep watering.
You can take the same total amount of fertilizer recommended for three applications and split it up into nine applications for every month from February to October. Nine light regular applications promotes better tree growth, especially for young trees.
But please don’t fertilize after October. You don’t want to promote new growth when there is danger of frost.