Chlorine and Plants

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January 6, 2020

This article originally appeared in Garden Culture Magazine UK32 & US30


Chlorine has been used as a disinfectant in city drinking water since the turn of the century, initially in the American city of New Jersey. As cities expanded and needed a longer-lasting disinfectant that would reach even the farthest tap, chloramines were introduced for their superior longevity. 

While chlorine continues to be used in many places, chloramines (made by combining chlorine with ammonia) are gaining in popularity as they are a better investment to keep waterlines free of biological contaminants. Water companies evaluate each water supply system individually and then decide which compound, and how much, will be used. 

One of the things we know about both compounds is that they are relatively safe for human consumption, regulated at 4 PPM, or parts per million. However, this is NOT the case for other organisms. Chlorinating your aquarium is pretty much a death sentence for anything living in it. When it comes to thriving crops, any grower wanting consistent, healthy yields needs to know the basics, starting with water chemistry.

Chlorine & plants, reverse osmosis.

A small amount of chlorine (in the form of chloride) is good for plants. Naturally occurring chloride is essential for photosynthesis, the uptake of carbon dioxide, and limiting water loss. 

However, once excess chlorine is introduced though city tap water, the vascular tissue of plants will accumulate the compound, which can result in “chlorine toxicity”. This condition manifests in what looks like the burning/yellowing of leaves, drop off, and ultimately, the death of the plant.

For those who grow hydroponically, chlorine and chloramines can be detrimental to root health. Helpful microorganisms such as beneficial bacteria, fungi, nematodes, mycorrhizae, and Trichoderma, all must have chlorine and chloramine-free water to support a root health ecosystem. These organisms protect roots, increase nutrient uptake, and can affect crop quality.

As water issues continue to become a global problem and the quality of tap water declines, it is not likely that chlorine and chloramines will be removed from the largest sources of public water. Cities even switch between using chlorine and chloramines throughout the year, making water quality unpredictable. As bacterial/organic contamination becomes more of a threat, so will the use of multiple antibacterial measures to help ensure municipal water is safe for consumption.

For growers with clean and stable city water quality, carbon filtration is still needed to remove chlorine and chloramines. Twice as much carbon media is necessary to remove chloramines as compared to chlorine. KDF or activated carbon are recommended for the most effective chloramine removal. 

However, the only way to make sure any water source is consistent and safe to use as a base for nutrient formulas is to use a reverse osmosis filter; especially in areas where water chemistry changes in response to fluctuating or seasonal contamination hazards.

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