Tips for Spring Citrus Fertilization

It’s February and time to fertilize our citrus trees to give them a boost before blooming this spring. Hopefully your trees are pruned up and in good shape after my column last week. Citrus trees are known for being “heavy feeders,” meaning they have relatively high nutrient requirements to thrive and be resilient compared to some other crops. Trees of course don’t eat fertilizer, but rather take it up from the surrounding soil through root hairs, which flow into feeder roots, and up into the tree to be utilized in growth processes, photosynthesis, and fruit production.

Our area benefits from relatively fertile soils with an average pH of around 6.8 to 8.2. A soil test will help home and commercial citrus growers in making precise applications of fertilizer for their trees, as well as any pH adjustments up or down with lime or sulfur. The ideal range for pH is 6.0 to 7.0, which ensures that most of the macro-nutrients (Nitrogen, Phosphorus, Potassium) and micronutrients (Zinc, Boron, Manganese, Magnesium, Calcium, etc.) are available to the tree’s roots to take up. From there, adjustments can be made.

Soil test results from LSU also give the soils’ levels of potassium, phosphorus, the micronutrients, organic matter, and salts. It’s usually a good idea to take a soil test each year or after a piece of land floods to give the trees a shot at thriving. Soil test kits are available at the AgCenter offices and a lot of the independent garden centers. Each box comes with a set of instructions, a test order form (choose “Citrus”), and three baggies for soil. To take your sample, use a plastic bucket to collect soil from 8 to 10 locations around the trees. Mix the samples and fill one of the baggies for each grove or grouping of trees. Label the baggies with a sharpie and mail the box (it is pre-addressed) to the LSU soil lab. Results typically take a week and are emailed and physically mailed to you, and will contain fertilizer rates for your trees based on the soil composition. This is the most precise way of fertilizing trees. Each tree gets exactly what is needed, and there is no wasted product. With the cost of fertilizer almost double, it’s worth the $16 lab fee to save some material.

Without a soil test, you can fertilize using the general guidelines suggested in the LSU AgCenter’s Home Citrus Guide (free online as a PDF, just search “LSU AgCenter Home Citrus Guide and it will come up!). The guidelines recommend fertilizing newly planted trees six weeks after planting. Wait until the newly planted trees show some signs of new growth, then spread half of a pound of 13-13-13 around the tree’s base. Half of a pound of fertilizer is roughly half of a cup. The newly planted trees can be fertilized as late as early April, just look for those signs of new growth before applying the product.

For mature trees, it’s best to apply our fertilizer in mid-February through early March. Early February is best since many of our trees will be blooming in March and it’s nice to get this finished before then. There’s a general guideline of applying one pound of 13-13-13 fertilizer per year that the tree has been in the ground, until you reach a maximum rate of 15 pounds per tree for 13-13-13. Spread the fertilizer along the drip line of the tree underneath the outer edge of the canopy, this is where the feeder roots are. Putting fertilizer right up to the trunk means it is less likely to be taken up by the tree. Try to spread the fertilizer evenly.

Fruit-bearing age citrus trees also benefit from a little extra nitrogen in June when the fruit crop is developing. Ammonium sulfate or Calcium nitrate are good to apply, or Urea if you can find it. For trees newly planted through their fourth year in the ground, spread a pound of nitrogen-rich fertilizer in June. For trees in their fifth year, do 1.25 pounds. Six year trees, 1.5 pounds, seventh year trees 1.75 pounds, and trees in the ground eight or more years, spread a maximum of three pounds. It’s good to increase the rate in June by a quarter of a pound each year of growth until hitting that maximum of three pounds. There is a handy chart with all of this information in the LSU AgCenter Home Citrus Publication. For more information on growing citrus at home, visit the LSU AgCenter website at www.lsuagcenter.com or www.louisianacitrus.org. You can also always reach me reliably at my cell Monday through Friday from 8 a.m. to 4:30 p.m. 312.846.0689 or email atimmerman@agcenter.lsu.edu. These are the best two ways of reaching me as we have had staffing disruptions in these strange pandemic times.