This week we will enlighten you on some of the important plant nutrients necessary for healthy woody ornamentals in the Florida landscape. We’ve had information about why the nutrient elements are needed and some of the problems caused when plants don’t get enough of them. But plants can almost always get enough of the element we’re discussing today, calcium. In fact, when calcium is a problem for landscape ornamentals it’s usually because there’s too much of it in the soil, not too little. Today you will find out why. My information was provided by Extension Emeritus Professor of Horticulture, Dr. Robert Black of the University of Florida, Institute of Food and Agriculture Sciences (IFAS).
Scientists have not found calcium deficiency to be a problem on woody ornamental plants growing in Florida landscapes. Several factors account for his, including the presence of calcium and calcium compounds in much of our water and in commercial fertilizers.
Calcium is important to plants for several reasons. It functions as a plant nutrient and it also indirectly affects soil fertility. For one thing, calcium helps maintain the right pH or acid level in the soil around your home.
This is important because it reduces leaching of ammonia, phosphorus and several other nutrient elements. In addition, keeping the right pH range in the soil encourages the growth of beneficial soil organisms, makes it easier for plants to utilize an element called molybdenum and reduces plant injury from toxic elements such as aluminum and excess copper.
In spite of all its beneficial effects, calcium can cause serious trouble for you or landscape plants if you have too much of it in your soil. High calcium levels increase soil pH beyond the desirable range, make it too sweet, or alkaline. This makes it harder for ornamental plants to take up several other important nutrient elements including iron, manganese, zinc, copper, boron, magnesium, potassium and phosphorous.
Fortunately, the amount of available calcium in most Florida soil is fairly low although there is usually enough for normal growth of landscape ornamentals. In very acid soils, it is occasionally necessary to add calcium by liming. As a rule you’d only lime an area you were planning to landscape if you had soil test results showing that the pH was too low.
You might remember from some of our previous articles about soil pH that the lower the pH numbers the higher the soil acid level. Anytime you have a soil pH below 5.5 or so, the soil acid level is higher than most landscape plants like. To raise the pH into the desirable range between 5.5 and 6.5 you need to add calcium to the soil.
Materials commonly used for this purpose are agricultural limestone, hydrated lime and dolomite. Dolomite contains calcium and another important element, magnesium. If you just need to change the pH level for your soil, agricultural limestone is probably the best material to use. However, many acid sandy soils in Florida re low in magnesium, so dolomite can be sued to raise the pH and supply magnesium at the same time.
As we said, the decision to use these materials should be based on soil test results. The amount you need depends on the soil pH you have, the soil type and the amount of organic matter in the soil.