The East Valley used to be citrus country, and plenty of backyards still have an orange, grapefruit or lemon tree that came with the house. Unlike the mesquites and palo verdes around them, citrus trees are heavy feeders. They need regular fertilizer to stay green and keep producing.
The tricky part is timing and amount. University of Arizona Cooperative Extension publishes a Citrus Fertilization Chart for Arizona (AZ1671) that takes most of the guesswork out of both. Here’s how to use it.
When to fertilize
UA Extension recommends splitting the year’s fertilizer into three equal feedings. The timing depends on what kind of citrus you have:
- Oranges, tangerines and grapefruit: one third in January or February, one third in March or April, and one third in May or June.
- Lemons and limes: one third in January or February, one third in March or April, and one third in August or September.
Notice what isn’t on the list: late fall. If you’re reading this in October or November, you can relax. Your next feeding is in January or February.
How much to use
The chart bases the amount on tree size, measured in pounds of actual nitrogen per year:
- Newly planted: none, or up to about 0.13 pounds once the tree is established and putting out new growth
- Small (2 to 3 feet tall): 0.25 to 0.5 pounds
- Medium (4 to 8 feet tall): 0.75 to 1 pound
- Large (10 feet and up): 1.25 to 1.5 pounds
Grapefruit and pummelo need only half those amounts. Lemons and limes need about 10 percent more.
Turning nitrogen into pounds of fertilizer
Every fertilizer bag lists three numbers, like 21-0-0 or 16-8-8. The first number is the percentage of nitrogen. To figure out how much product you need, divide the pounds of nitrogen by that percentage.
Say you have a medium orange tree that needs 1 pound of nitrogen a year, and you’re using a 21-0-0 fertilizer. That’s 1 divided by 0.21, or about 4.8 pounds of product for the whole year. Split three ways, it comes to roughly 1.6 pounds per feeding. UA’s chart has this math already worked out by fertilizer type if you’d rather look it up.
How to apply it
- Measure it. Eyeballing is how trees end up burned or underfed.
- Spread it under the canopy, out toward the drip line where the feeder roots are, and keep it off the trunk.
- Work it lightly into the soil.
- Water it in right away, and water deeply.
Still seeing yellow leaves?
If you’re feeding on schedule and the tree still looks off, fertilizer may not be the issue. New leaves that come in yellow with green veins usually point to iron chlorosis, which is tied to our alkaline soil. Yellowing can also come from overwatering, poor drainage or root problems. Our post on whether desert trees need fertilizer goes into how to tell the difference.
Planting a new citrus tree? Do it in spring after the danger of frost has passed. Our guide on when to plant trees in Gilbert covers the rest.
Let us take care of it
Heartwood offers tree fertilizing in Mesa, Gilbert, Chandler Heights, Sun Lakes and throughout our service area. If a tree is struggling and you’re not sure why, a tree consultation can pin it down. We also do tree trimming and the rest of our tree care services. Request a free estimate or call (480) 269-5636.
Sources
- University of Arizona Cooperative Extension, Citrus Fertilization Chart for Arizona (AZ1671)
- University of Arizona Cooperative Extension, Fertilizing Woody Ornamentals (Backyard Gardener #212)
