Labor Day means that it’s time to fertilize your citrus trees! We fertilize three times a year here in Arizona, and the last time of the year is right now, in early September. If you’re looking for general information about fertilizing citrus, follow this link to a blog post that we made earlier this year, when it was time to feed in mid-May. For September’s citrus feeding post, we’ll be talking a little bit about what’s in a citrus fertilizer.
All fertilizers list the nutrients that they contain in the form of three numbers printed on the packaging. The first number always represents Nitrogen, the second number is for Phosphorus (phosphoric acid, or phosphate), and the third number is Potassium (potash). Specifically, the number for each nutrient tells us what percentage of the fertilizer is made up of that nutrient. For example, if you had a 100 lb bag of fertilizer that was labeled with the numbers 15-15-15, you would know that the bag contains 15 lbs of each nutrient. A 5 lb bag of the same fertilizer would only contain 3/4 of a pound of each nutrient.
Recommendations for fertilizing citrus are typically given in the amount of nitrogen to apply throughout the year, so it’s important to know exactly how many pounds of this nutrient you’re using when you feed your trees. Many people use an all-purpose fertilizer to feed their citrus, which is absolutely fine. You can also purchase fertilizers that are formulated for the specific needs of citrus or fruiting trees. Whichever you use, pay attention to the amount of nitrogen you’re applying. Applying too much can burn the roots, and applying too little can leave your tree hungry for more.
So what does nitrogen do for our trees, and why is it important? Nitrogen is the nutrient that helps plants put on new growth and produce chlorophyll (the green pigments in leaves that convert sunlight to food). Without enough nitrogen, growth will be stunted, and your citrus tree’s leaves may begin to turn yellow.
The second number, phosphorus, aids plants in root development and flower formation. This nutrient is especially important for new plants, but it isn’t typically provided in large amounts in a citrus fertilizer. Products aimed at boosting flower power or helping plants get established have more phosphorus than nitrogen or potassium, while fertilizers aimed at feeding fruit trees often have less phosphorus than the other two nutrients.
Potassium, the third number on the label’s analysis, is said to aid in overall plant health. It helps the plant utilize water efficiently, and also helps it to resist pests and disease. In citrus, potassium is the nutrient that has the most impact on size, yield, and quality of fruit.