Purchasing water-soluble fertilizer for your crops is not simply based on what is on sale or a matter of selecting a “geranium fertilizer” for your geraniums; it is based mostly on the quality of your water source. Water can have a significant impact on the pH of the growing medium and may also provide sufficient levels of certain beneficial nutrients, keeping them off your fertilizer program. To develop a fertilizer program, have the water tested for alkalinity, nutrient levels and electrical conductivity (EC) for the content of total salts.

What is alkalinity?
To develop a fertilizer program, begin with testing the alkalinity of your water. Alkalinity is not a measure of pH, but a measure of the bicarbonates and carbonates present in the water and is expressed in parts per million (ppm) calcium carbonate. Essentially, alkalinity is a measure of the quantity of “limestone” dissolved in the water. Therefore, the higher the alkalinity of a water source, the more “limestone” is applied with each irrigation and the faster the pH of the growing medium rises.

This rise can be offset by using a potentially acidic fertilizer and/or injection of acid to neutralize some of the alkalinity into a desirable range. Likewise, if the alkalinity is low, then use a fertilizer with a low potential acidity or even a fertilizer with a potential basicity.

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