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The chart below and citrus fertilization calculator provides the homeowner with practical instruction and on how much commercial fertilizer to apply and when to make those applications their citrus trees.
Using the chart
- On the left edge of the chart, find a description of the tree you wish to fertilize. Since commercial citrus fertilizer application recommendations are based either on tree height, trunk diameter or the area of the ground covered by the canopy, ranges of all three measurements are included in the tree descriptions. The total pounds of actual nitrogen recommended by the University of Arizona for a tree for one year are found in the gray column directly to the right. Since no fertilizer is 100% nitrogen, use the chart to determine the amount of a specific type of fertilizer needed by your citrus tree.
- Look at the top edge of the chart for the percent nitrogen which your fertilizer contains. Remember that every container of fertilizer has 3 numbers written on it. The first number indicates the % nitrogen, the second the % phosphorus as available phosphate (P2O5), and the third the % potassium as available potash (K2O). For example: 9-6-4 has 9% nitrogen, 6% phosphorus and 4% potassium – see illustration.
- The intersection of the row describing your tree, and the column indicating % nitrogen of your fertilizer, is the recommended range of pounds of that particular type of fertilizer to use during the entire year for oranges, tangerines and other exotic citrus. For grapefruit and pummelo, apply ½ of this amount annually, and for lemons and limes, apply about 10% more than the amount in the chart annually.
- For oranges, tangerines, and grapefruit, apply ⅓ of the recommended range of fertilizer in January-February, ⅓ in March-April and ⅓ in May-June.
- For lemons and limes, apply ⅓ of the recommended range of fertilizer in January-February, ⅓ in March-April and ⅓ in August-September.
Example 1
You have a small, 2-foot tall lemon tree, and a bag of citrus food (13-10-4) which has 13% nitrogen. Find the row for a small tree. Then, find the column for 13% nitrogen. They meet at the number 1.9 to 3.8. Because the tree is a lemon, add about 10% to the total (2.10 to 4.2 lbs.). Since the tree height is at the low end of the range, apply 2.10 lbs. of the citrus food during the year. Apply ⅓ (about 0.7 lbs.) during January-February, ⅓ in March-April, and ⅓ in August-September.
Example 2
You have a large, 10 foot tall adult grapefruit tree, whose canopy covers about 100 square feet of the ground surface and you have citrus fertilizer with 6 % nitrogen (6 is the first of the three numbers on the bag). The row for this tree and the column for 6% nitrogen join at the numbers 20.80 to 25.00. Mature grapefruit trees require only half of the amounts listed in the table. Therefore, this tree will require about 10.4 to 12.50 lbs. of fertilizer annually. Apply about 3.5 to 4.0 lbs. (⅓ of the total) during January- February, ⅓ in March-April and ⅓ in May-June.
Annual fertilizer requirements
Use this chart to compare pounds of nitrogen needed per year to the percentage of nitrogen found in fertilizers so you know you're applying the correct amount. Often, nitrogen within fertilizer is written as the first number written on the fertilizer packaging. The chart is applicable for oranges, tangerines, tangelos and other exotic fruits. For grapefruit, pumelo, lemons and limes:
- For oranges, tangerines, and grapefruit, apply ⅓ of the total in January-February, ⅓ in March-April and ⅓ in May-June.
- For lemons and limes, apply ⅓ of the total in January-February, ⅓ in March-April and ⅓ in August-September.
To convert from decimal to ounces, multiply the decimal portion of the number by 16. For example, using 6.25 lbs. of fertilizer, multiply 0.25 x 16 = 4 ounces, giving 6 lbs. 4 oz. Measure accurately before applying and always incorporate fertilizers in the soil and follow with irrigation.
| Tree size | Pounds of actual nitrogen required for the year | 4% Nitrogen | 5% Nitrogen | 6% Nitrogen | 8% Nitrogen | 10% Nitrogen | 14% Nitrogen | 16% Nitrogen | 21% Nitrogen (ammonium sulfate) | 46% Nitrogen (urea) |
|---|---|---|---|---|---|---|---|---|---|---|
| Newly Planted Tree You may apply small amounts of nitrogen after tree is established and new growth has emerged | None to 0.13 lb. | None to 3.0 lbs. | None to 2.5 lbs. | None to 2.0 lbs. | None to 1.5 lbs. | None to 1.2 lbs. | None to 0.9 lbs. | None to 0.75 lbs. | None to 0.6 lbs. | None to 0.25 lbs. |
| Small Tree 2 to 3 feet tall, up to 1.25” trunk diameter and up to 9 sq. ft. of ground area covered by the canopy | 0.25 to 0.50 lb. | 6.25 to 12.50 lbs. | 5.00 to 10.00 lbs. | 4.20 to 8.40 lbs
| 3.10 to 6.25 lbs
| 2.50 to 5.00 lbs
| 1.90 to 3.80 lbs
| 1.60 to 3.20 lbs
| 1.20 to 2.40 lbs
| 0.50 to 1.10 lbs.
|
| Medium Tree** 4 to 8 feet tall, 1.25” to 4.0” trunk diameter and from 16 to 64 sq. ft. of ground area covered by the canopy | 0.75 to 1.00 lb. | 18.75 to 25.00 lbs. | 15.00 to 20.00 lbs. | 12.50 to 16.75 lbs. | 9.40 to 12.50 lbs | 7.50 to 10.00 lbs. | 5.80 to 7.70 lbs. | 4.70 to 6.50 lbs. | 3.60 to 4.80 lbs | 1.60 to 2.20 lbs |
| Large Tree 10 feet tall or more, 6 to 10” trunk diameter and more than 64 sq. ft. of ground area covered by the canopy | 1.25 to 1.50 lbs. | 31.25 to 37.50 lbs. | 25.00 to 30.00 lbs. | 20.80 to 25.00 lbs. | 15.60 to 18.75 lbs. | 12.50 to 15.00 lbs. | 9.60 to 11.50 lbs. | 7.80 to 9.40 lbs. | 6.00 to 7.10 lbs. | 2.70 to 3.30 lbs. |