One very important aspect of hydroponic gardening is maintaining consistent parameters in the nutrient solution. After all, the nutrient solution is where the plant derives all its nutrition for growth. In a hydroponic system, there are many variables which all play vital roles in the plant’s ability to uptake and use nutrients. In addition to having control over lighting and ventilation, every hydroponic gardener must have the ability to control the parameters of their nutrient solution.
All hydroponic gardens are different so there is no “one-size-fits-all” technique or product that will maintain a consistent hydroponic nutrient solution. However, a better understanding of each individual parameter and how it affects growth in the garden will give hydroponic gardeners the knowledge to maintain parameters as close as possible to optimal levels. The four most important parameters that affect the way plants respond to a hydroponic nutrient solution are pH, concentration of nutrients, temperature, and dissolved oxygen content.
Potential Hydrogen (pH)
The potential hydrogen, or pH, scale is a system of measurement that determines the concentration of hydrogen ions. In a garden, the pH scale is used to measure the acidity or alkalinity of a growing medium, water source, or nutrient solution. The pH scale consists of number values between 0 and 14 (with 7 being pH neutral). A neutral pH means the substance being measured has neither an acidic nor an alkaline pH, but instead sits directly between the two. Numbers on the pH scale below 7 represent acidity while numbers above 7 represent alkalinity.
It is important to remember that the pH scale is an exponential logarithmic scale. In other words, the intensity of the acidity or alkalinity increases exponentially as the value gets farther away from the neutral point of 7. In fact, each number on the pH scale represents an increase or decrease in potential hydrogen by ten-fold. This means that a pH value of 4 is ten times more acidic than a pH value of 5 and is 100 times more acidic than a pH value of 6. As pH values increase above 7, the same holds true for alkalinity. For example, a pH value of 10 is ten times more alkaline than a pH value of 9 and is 100 times more alkaline than a pH value of 8.
In a hydroponic solution, the pH value will influence the plant’s availability to absorb nutrients. Put another way, there is a pH range that is most suitable for nutrient absorption. If the pH level moves too far from that suitable range, certain elements will become “locked out” or unavailable to the plants. The ideal pH range for nutrient absorption for most plants in a hydroponic system falls in the 5-6 pH range. The maximum absorption range for many plant species falls in the 5.5-5.8 pH range. Hydroponic systems do not have a medium to buffer the pH like plants in soil and, because of this, the pH value can fluctuate more rapidly. This is one of the reasons why it is so important for hydroponic gardeners to monitor the pH levels of their nutrient solutions on a regular basis.
When pH fluctuations occur, it is important for hydroponic gardeners to catch it quickly and to correct the pH of the nutrient solution. As with other aspects of hydroponic horticulture, consistency is the key. The more consistently a grower can keep their nutrient solution within the desired pH range, the more efficiently the plants can uptake nutrients allowing the plants to grow at a fast rate.
The concentration of nutrients in the water is another critical factor for a hydroponic nutrient solution. Just about every nutrient manufacturer has its own suggested nutrient concentration for hydroponic applications. This is usually expressed in either parts per million (PPM), total dissolved solids (TDS), or electric conductivity (EC). PPM is a form of measurement used to determine the concentration of diluted substances. One PPM is equal to 1 milligram of substance per liter of water. In hydroponic gardening, PPM and TDS are used to express the amount of nutrients in the water. PPM and TDS are just different terms that express the same thing. These measurements are taken by using an electronic conductivity device that automatically converts the EC reading into a PPM/TDS format. Some of the older meters do not convert the EC values into a PPM or TDS value. In this case, the gardener can either make the calculation to determine the PPM/TDS or use the EC value itself as a reference point.
Just like pH monitoring, it is important for a hydroponic gardener to regularly check the nutrient concentration of the nutrient solution. If the concentration becomes too low, the plants may not be receiving all that they need to sustain accelerated growth rates. This may lead to slowed growth and/or nutrient deficiencies. If the nutrient solution becomes over concentrated, this can cause serious burning or lock out issues, which can also lead to nutrient deficiencies. Put another way, when the concentration of nutrients is not consistently kept in the desired range, the plants will not be able to perform up to their full potential. Unfortunately, the nutrient manufacturer’s suggested dosage is just a starting point. It is ultimately up to the grower to determine the appropriate nutrient concentration depending on the stage of growth, type of crop, and environmental factors, such as enriched CO2 levels.
The temperature of a hydroponic nutrient solution is another pivotal factor in achieving success. For most hydroponic systems, the ideal temperature should fall in the 65-72 degrees F range. It is important to remember that in most hydroponic systems the nutrient solution is taken from the reservoir and then makes direct contact with the plant’s roots. Because of this, the root mass of the plant will be greatly affected by the temperature of the nutrient solution. If the nutrient solution is too cold, the plant’s ability to uptake nutrients will slow down. In extreme cases, cold temperatures in the nutrient solution can cause the plant to stop taking up nutrients all together. When a nutrient solution is too cold, the plants will show signs of stress that often mimic nutrient deficiency symptoms. This can make it hard to correctly identify temperature as the culprit. Regular monitoring of the nutrient solution’s temperature is imperative for hydroponic gardeners.
While monitoring the reservoir for cold temperatures is important, most hydroponic gardeners are battling the other end of the spectrum: heat. When the temperature of a nutrient solution rises above the desired range, it can adversely affect the way the plants grow. In fact, a nutrient solution with a temperature that is too warm will open up the possibility of pathogens that can quickly destroy an otherwise healthy hydroponic garden. The main reason why too warm temperatures are detrimental in a hydroponic system is because of the way temperature affects the dissolved oxygen content.
Dissolved Oxygen Content (DO)
In layman’s terms, dissolved oxygen is oxygen (O2) in gas form held in-between the water molecules. Dissolved oxygen levels in tap water are typically between 5-7 PPM at room temperature. Fully oxygenated water at 68 degrees F will hold about 9 PPM of DO. As the temperature of a nutrient solution increases, its ability to hold gas (O2) decreases. In other words, the warmer the water, the less dissolved oxygen it contains. When the temperature of a nutrient solution becomes too warm and the dissolved oxygen content decreases, the possibility of anaerobic pathogens increases. Anaerobic pathogens can only take hold in an oxygen-depleted environment. Root rot is the most common anaerobic pathogen to plague hydroponic gardens with warm water temperatures.
To maintain high levels of dissolved oxygen, horticulturists need to have control over the nutrient solution’s temperature. Perhaps the most effective way to control temperatures in a hydroponic system is to invest in a water chiller. A water chiller is a device much like an air conditioner, but for water. The nutrient solution can be cycled through the water chiller and, ideally, chilled to the desired temperature range. Many hydroponic gardeners also use electrolysis devices which separate the oxygen and hydrogen from water molecules. In the process, the electrolysis increases the amount of dissolved oxygen in the nutrient solution.
Maintaining consistent parameters in a nutrient solution is crucial to having a successful hydroponic system. Potential hydrogen (pH), nutrient concentration (PPM,TDS, EC), temperature, and dissolved oxygen (DO) each play their own important roles in the crop’s ability to uptake and use nutrients. Hydroponic gardeners who understand each of these parameters and how each affects the garden will be able to more quickly identify problems and more seamlessly implement the parameters needed to sustain accelerated growth. In a hydroponic system, the nutrient solution is, in many ways, the equivalent of soil. In other words, all of the plant’s nutrition and the root’s access to oxygen comes from the nutrient solution. When all the parameters of a nutrient solution are dialed in to the desired range, the plants will have access to the nutrients and oxygen they need to produce vibrant and abundant yields.
Eric Hopper resides in Michigan’s beautiful Upper Peninsula where he enjoys gardening and pursuing sustainability.