Hydroponic Systems and Nutrient Cycling

Hydroponic systems can be very elaborate, large scale and even automated from start to finish. They can also be simple, small and for home use but one thing they all have in common is nutrient cycling. The nutrient solution must be changed, or cycled, every two to four weeks depending on various factors.

It starts with the water source. After all, hydroponics is the production of plants in a water medium rather than soil. The water source should be tested before any additional nutrients or conditioners are added. Just like in soil, the pH must be addressed first. If the pH is too high, or too low, there may be nutrient availability issues. The solution should have a target pH of 5.5 to 6.0 for maximum required nutrient availability for most commercially grown crops. If the solution is too low, or acidic, there may be less available calcium and magnesium. If it is too high, or basic, many of the micronutrients and phosphorus are not available. Ammonia based nitrogen products tend to decrease pH and nitrate forms tend to increase pH in the nutrient solution.

The EC, or electrical conductivity, measures the water’s ability to conduct an electrical current. Salt concentration, minerals, metals and solids in the solution will increase the EC value. If the solution starts at a concentration higher than the desired threshold, it will only continue to increase as soluble nutrients are added to the solution. A starting EC of 1 mmhos/cm or less is desirable.

Not all nutrients are taken into the plant at the same rate, or speed. Phosphorus can accumulate over time in the solution due to slower uptake and is added back in most nutrient mixes at full strength. Other micronutrients and metals will accumulate over time at toxic levels if the solution is not cycled. Hydroponics is a balancing act, and once the EC gets too high from salt accumulation the roots will “burn” and decrease growth. Without a good root system, the plant will not have proper nutrient uptake.

The simple way to start with a consistent nutrient solution is to filter the water source using reverse osmosis. This ensures a clean starting point to add nutrients. Once the nutrient package is added, a water analysis can be used to know when it needs to be cycled out. Depending on the scale of the operation, this can be a very cost-effective way to manage nutrient levels and knowing when to cycle out the current solution.

Always sample the water source before adding nutrient packages. This will prevent costly mistakes like high EC levels, aid in the correction of hard water, management of pH and provide sufficient nutrients for the crops. Sampling the water source, in conjunction with sampling nutrient solutions, is the most effective way to manage a hydroponic system.

Fernandez, D. (2020, October 11). Factors limiting the life of a recirculating hydroponic nutrient solution. Science in Hydroponics. https://scienceinhydroponics.com/2020/10/factors-limiting-the-life-of-a-recirculating-hydroponic-nutrient-solution.html

Ronzoni, R., & Mattson, N. (2020). A guide to home hydroponics for leafy greens. Cornell University Controlled Environment Agriculture Program. https://bpb-us-e1.wpmucdn.com/blogs.cornell.edu/dist/8/8824/files/2020/05/Guide-To-Home-Hydroponics-For-Leafy-Greens.pdf