Let’s talk nutrition
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As with all plants, citrus trees make their own food through the process of photosynthesis. That "food" is strictly glucose which only contains the elements carbon, hydrogen and oxygen. All plants require additional nutrients to make necessary plant parts, plant proteins and other important ingredients. These additional nutrients are contained in fertilizers. In a natural environment, there is a cycle where dead plant and animals remains are broken down into these nutrients needed by the plants.
Backyard citrus is not a natural environment therefore chemical or organic fertilizers must be added to the plants in order for them to thrive and produce good quality fruit. However, this addition of fertilizer to the soil must be done while also minimizing environmental impacts. Right fertilizer source, right rate, right time and right place is therefore very important.
The three big nutritional requirements are nitrogen, phosphorus and potassium usually abbreviated as NPK. A bag of fertilizer usually has numbers recorded. The numbering of 10-10-10 indication 10% nitrogen, 10% phosphorus and 10% potassium. Nitrogen is of special importance because plants need this nutrient in large amounts. Nitrogen is also easily lost from soil and fairly expensive to supply. Nitrogen has numerous functions in plants and essentially all life processes depend on this nutrient. Nitrogen deficiency first appears on older leaves and then proceeds toward younger leaves. Deficiency symptoms are characterized by light yellowish green leaves. The veins are only slightly lighter in color than the tissue between them.
Phosphorus is present in all living tissue. Phosphorus is needed for photosynthesis, synthesis and breakdown of carbohydrates and the transfer of energy within the plants. This nutrient helps plants to form seeds, develop roots, speed maturity and resist stress. Florida soils have a sufficient amount of phosphorus therefore phosphorus deficiency is not common in Florida citrus. Fertilizers are produced for a wide range of soil conditions throughout the country therefore if possible one should opt for a low second number when purchasing fertilizers.
Potassium, also called potash, is one of the most important nutrients applied as fertilizer in Florida. Potassium plays a key nutritional role in determining yield, fruit size and quality. Florida sandy soils are naturally low in potassium thus potassium fertilizer application is required every year. A characteristic yellowing of the leaves, small fruits and necrotic spotting of leaves indicated potassium deficiency.
In addition to the big three, there are a number of micronutrients that play important roles in citrus production. To name a few of these nutrients: iron, copper, calcium, magnesium and several others. Therefore, it is very important to purchase a citrus fertilizer.
Several brands are on the market and can be purchased at any nursery or big box store. It is recommended to spread the fertilizer application out over the year. Please keep in mind that there is a fertilizer ban in Lee County between June 1 and Sept. 30.
Another necessary requirement for good citrus production is water. In the spring and especially this year there is not enough rainfall to fill this requirement. Irrigation water is not enough. To keep citrus healthy and produce good quality fruit, it is necessary to supplement the rainfall and irrigation with a good soaking two or three times a week. Just let the hose trickle water on the ground until the area under the canopy is thoroughly moistened.
Happy citrus!
Kathy Woodlock is Past President Garden Club of Cape Coral, a Master Gardener/citrus advisor and NGC Flower Show Judge.