There’s a lot to concentrate on if you’re to keep your plants healthy and reap the best harvests: The right light, proper humidity, correct temperatures for their growth stage, preventing powdery mildew… and providing dissolved oxygen to your plants’ roots.
What is dissolved oxygen?
Water is made up of hydrogen and oxygen atoms bound together. However, there’s a different form of oxygen hanging out between those water molecules: Molecular oxygen (O2). Molecular oxygen, also known as dissolved oxygen or DO, is used by plant roots for growth.
Editor’s Note: Water is an excellent solvent because it is a polar molecule.
Most water sources naturally contain some DO; the amount contained in outdoor bodies of water varies depending on pollution, water temperature, water aeration (moving streams contain more DO than still lakes) and other factors. Even ordinary tap water contains some DO (usually 5 to 7 parts per million, or PPM) at room temperature. In most grow rooms, you’ll be controlling the amount of DO in the water you use, usually ranging from about 7 to 10 PPM.
Why do plants need DO?
The plants in your grow room’s hydroponic system need dissolved oxygen (DO) in their water if they are to thrive and provide the best yields. Plant root systems use oxygen for aerobic respiration, and with a hydroponic system, most oxygen used in root uptake is in the nutrient solution. If plant roots don’t get enough oxygen, they become less permeable, take in less water, and can no longer absorb nutrients properly. Toxins also begin to build up. If oxygen deprivation continues, plants begin to “starve” from lack of nutrition. Roots begin to die, and plant growth is stunted. Ultimately, pathogens can take over and finish off the weakened plant.
Water purity affects DO levels in water
Standard tap water usually contains other elements, like chlorine, which reduce the amount of oxygen tap water can hold. Water’s salinity is also a factor: The higher the salinity, the less soluble the oxygen, resulting in lower DO levels. Normal nutrients you add to the water do the same thing. Contaminants like bacteria will also reduce the amount of DO available to plant roots.
Editor’s Note: Think of the potential dissolution capacity of water as a limited resource. Salts, bacteria, and nutrients will all consume some of the dissolution capacity, leaving less room for water to dissolve.
For all of those reasons, many growers opt for reverse osmosis filtered water, with just enough nutrient solids added to meet plants’ nutritional needs. Dehumidifier water can also provide a “free” and endlessly renewable supply of water that may be preferable to reverse osmosis filtered water.
Temperature affects DO levels in water
Temperature also affects how much DO water can hold. The lower the water temperature, the more oxygen it can hold; the higher the temperature, the less it will hold. Water that is fully oxygenated or 100% “saturated” with DO at the grow room temperatures optimal for plant growth will be in the ~7 to 10 PPM range.
Editor’s Note: Water is better at dissolving solids when it is warm, and better at dissolving gases (such as oxygen and carbon dioxide) when it’s cold. There is a tradeoff to be made with water temperature.
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About the Author
Quest builds quality, energy-efficient dehumidification equipment designed to perform in commercial environments. Quest has the solution for any indoor or greenhouse gardening application. Quest dehumidifiers are extremely energy efficient on the market, removing the most pints of water per kWh over the widest temperature range.