My question is about citrus trees. What is best to fertilize them with? Organically if possible. I sometimes notice a lot of flowers, but the fruit falls off. Does a tree need more nitrogen? What is the best fertilizer?
My question is about citrus trees. What is best to fertilize them with? Organically if possible. I sometimes notice a lot of flowers, but the fruit falls off. Does a tree need more nitrogen? What is the best fertilizer?
There are two answers to this question:
1. I have not seen any research data showing one garden fertilizer is significantly better than another. However, testimonials from gardeners will declare that some are superior; these products usually come with a higher cost.
2. For all practical purposes there is no best fertilizer. In the broadest sense, nitrogen is nitrogen (N), phosphorus is phosphorus (P), and potassium is potassium (K). Plants only absorb nutrients that have been broken down into inorganic, water-soluble forms. For example, whether nitrogen comes from brand A or B, whether it was derived from anhydrous ammonia (gas) or urea, or from manure or the compost pile, it makes no difference to the plant. Until you find something that is outstanding, my recommendation is stick with a basic N-P-K, buy on sale, and don’t fall for gimmicks.
The question now is what type of formulation to purchase?
Nitrogen only, potassium only, phosphorus only, or combinations? Nitrogen is always needed in areas of heavy rainfall, because it is easily leeched out of the soil. Fertilizers like ammonium sulfate, ammonium nitrate, urea and calcium nitrate are all good fertilizers for supplying nitrogen. Calcium nitrate will also give calcium, but it is more expensive. Like nitrogen, potassium can also move in the soil with water, while phosphorus does not. The question of whether to apply potassium and phosphorus can be answered accurately by a soil analysis. Without an analysis, statements about soil fertility are only guess work. If an analysis is not taken, then buying a fertilizer with all three ingredients (N-P-K) is a good idea. The only problem with that is if the soil has adequate phosphorus, and over the years more is added, a soil imbalance may occur, and the excess phosphorus will cause a deficiency in iron and zinc — seen as interveinal chlorosis, a yellowing between the veins. Also, it is cheaper to supply nitrogen than all three nutrients. Or, you can apply nitrogen alone and supply the potassium and/or phosphorus only when deficiency symptoms occur. (You will have to read up on those symptoms!)
Sometimes micronutrients are added to an N-P-K formulation. But they are added at such low amounts, they do little to help the tree.
My advice is not to pay more for the added micronutrients. Special formulations of ‘citrus food’ or ‘avocado food’ or ‘palm food’ are good fertilizers. But note that they are higher priced, and a basic all-purpose fertilizer should work as well. Organic vs. Inorganic.
Inorganic fertilizers often contain rather high percentages of the major nutrients and are applied on a ‘per pound per acre’ basis.
Organic fertilizers, on the other hand, have relatively low amounts of nutrients and are applied on a ‘per ton per acre’ basis. Although organic fertilizers have many benefits, including improving soil structure, conserving moisture and feeding beneficial microorganisms, they are rather expensive in Hawaii; gardeners should take advantage of any free or cheap supply of manure.
For more information, see www.gardenguyhawaii.com “What’s So Hot about Manure?” under the fertilizer label. Placing compost and/or organic mulch around citrus trees is a benefit and will over the years release nutrients.
Note: Don’t pile the materials against the trunk since moisture held there can lead to crown root.
Hilo resident Nick Sakovich is a professor emeritus of the University of California. He has worked in the field of agriculture for 30 years, and is a member of University of Hawaii Master Gardeners. E-mail your questions to Sakovich at askthegardenguy@earthlink.net.