The selection of a nutrient solution formulation is an important decision for the hydroponic grower—not only in terms of plant performance considerations, but in terms of cost and compatibility with the growing method being employed.

It is not possible to combine all of the required elements necessary to formulate a nutrient solution in a single liquid concentrate. This means that the hydroponic grower has three options, which include using:

  • liquid concentrates that contain an element or suite of elements
  • single or multiple-element reagents in their solid form (table one)
  • homogenized mixtures of reagents in solid form

Each of these methods has their advantages and disadvantages, based on ease and suitability of use. Weighing each individual reagent offers the greatest flexibility in preparing a formulation, while the use of the other two options is limited to what is commercially available and is therefore of limited flexibility.

In today’s marketplace, liquid concentrates are readily available in a wide range of formulations, some designed for specific applications in terms of plant status or growing method.

These liquid concentrates contain an element or suites of elements—the number and volume of such concentrates required to constitute a nutrient solution determined by whatever formulation is being made.

Such concentrates appeal to the small-scale grower due to their ease of handling, although the obtained formulation might not be the most desirable for the plant species being grown or the hydroponic growing method employed.

In some instances, a concentrate might contain a substance or substances that the gardener does not require for his particular grow—in this case, the grower must make a compromise based on the best-option result. Some concentrates are suspensions—not true solutions—which must be well mixed (shaken) when drawing an aliquot. The aliquot should then be allowed to go into solution before the next concentrate is added.

Formulating a nutrient solution by weighing reagents into a specific volume of water provides the grower with the greatest flexibility in terms of elemental concentration in the solution, but requires the ability to accurately weigh each reagent (see table one). In my book (Jones, 2005, pages 90 to 100), I list numerous nutrient solution formulations using elemental source reagents—many formulations having designated use applications.

The grower might find the preparation of the micronutrient portion of the nutrient solution tedious and challenging and the handling and storage requirements for these reagents can also be a nuisance. For the large volume user, however, this is the best option available. Depending on grade, the quality of the reagents can be a factor that can affect solubility and freedom from unwanted contaminates. When preparing concentrates, making the solution acidic and warming it can significantly affect dissolution.

The purchase of a solid matrix of reagents makes for ease of handling but limits the user to what has been selected for inclusion in the element mix. There are nutrient solution formulation mixes that can be prepared by volume measurement and do not require an analytical balance—a solid matrix formulation recipe is given in my book (Jones, 2011, pages 64 to 65). For the large-volume user this choice can be appealing based on the ease of preparing the nutrient solution, although the formulation might not be the most ideal for the plant species being grown or the hydroponic method being employed.

After a nutrient solution is formulated and ready to be used, it is a good idea to check the pH and electrical conductivity (EC) and to have the solution assayed for its elemental content to verify that all the required elements are present at their optimal concentrations.

Most hydroponic growers have limited knowledge regarding the effect that use factors have on how a selected nutrient solution formulation will affect plant growth and the nutritional status of the plants, those factors being the volume of nutrient solution supplied with each application and the frequency of application.

There is a correlation between the elemental concentration in a nutrient solution formulation and the volume of nutrient solution applied with each irrigation. In general, the greater the volume of nutrient solution applied with each irrigation, the weaker the elemental concentration can be, so that the actual elemental exposure is equal. In fact, as the elemental concentration declines, there are less synergistic and antagonistic interactions among the element ions that can affect nutrient element root absorption. With increased frequency of nutrient solution applications or a higher elemental concentration there is an increase in the potential for elemental ion accumulation—frequently referred to as ‘salts’—and elemental combinations resulting in the formation of precipitates in the rooting medium, both undesirable conditions that can adversely affect the nutritional status of your plants.

For some growers making a selection from what is available commercially as concentrates—either liquid or solid—might be sufficient. However, for the commercial grower the use of source reagents is the best option since the elemental content of the prepared nutrient solution formulation can be specifically set and combined with the use factors to minimize the potential for plant nutrient element insufficiencies.

References:

Jones, Jr., J. Benton, 2005, Hydroponics: A Practical Guide for the Soilless Grower, CRC Press, Boca Raton, FL.

Jones, Jr., J. Benton, 2011, Hydroponic Handbook: How Hydroponic Growing Systems Work, GroSystems Inc., Anderson, SC.