To understand the mechanics of nutrient lockout and how to prevent it from occurring, you must first have a basic understanding of how plants take in nutrients. (WARNING! Science content!) Most of a plants sustenance is taken in through the roots through a process called osmosis. Osmosis is the physical process by which a solution of low concentration translocates through a semi-permeable membrane to a solution of higher concentration on the other side of the membrane. This process is what allows roots to absorb water from the surrounding soil. As osmosis occurs, energy is released and used to fuel plant growth. Now enter nutrient lockout.
The passage of water and nutrients through the root membrane is controlled by the relative concentrations of individual nutrient elements on either side of the membrane. If the concentration is higher in your grow medium than in the roots, then the plant can dehydrate by releasing water and nutrients from inside of the roots to the grow medium.
So, in laymans terms, if you have a very high concentration of nutrients going to your grow medium then you can seriously mess up the plants biological processes. For hydroponic hobbyist, this usually occurs because of an adjustment to the nutrient solution in the reservoir to compensate for a nutrient deficiency. Since nutrient lockout has the same symptoms as nutrient deficiency, it is often hard to diagnose and recover from.
The passage of water through the semi-permeable membrane is controlled by either the TDS (total dissolved solids) or EC (electrical conductivity) of the nutrient solution. So, if the EC of the solution you’re feeding is excessively higher than the EC currently in the roots, the plant can dehydrate by drawing water out of the roots and into the medium via osmosis.
The best defense against nutrient lockout is to routinely monitor your nutrient solution at the reservoir topping off as needed and flushing every two weeks.
Macronutrients
Macronutrients are the core elements that are most needed by plants. The three major macronutrients are: Nitrogen “N”, Phosphorus “P”, and Potassium “K”. If you have ever purchased any type of fertilizer, then you will recognize these letters. All fertilizers consist of these elements in varying quantities. This is also referred to as the N-P-K ratio of the fertilizer and can be found on the side of the bag (20-20-20). Based on these three numbers you can choose a fertilizer that meets the needs of your plants during the different stages of growth. Most vegetables thrive primarily on “N” and “P” during the vegetative stage and in their flowering-stage, “P” and “K”.
Micronutrients
In addition to macronutrients, plants also require trace-elements for optimum growth. These trace-elements or micronutrients include:
- Calcium - Ca
- Magnesium - Mg
- Sulfur -S
- Manganese - Mn
- Boron - B
- Zinc - Zn
- Copper - Cu
They are present in many fertilizers, but in much less quantities than macronutrients.