Chlorine has a number of benefits to plant growth. Many people make the common mistake of mixing up the plant nutrient chloride (Cl-) with the toxic form chlorine (Cl). Chloride is vital for many different plant functions, despite only being classified as a micronutrient. It is highly essential, combined with the element potassium (K+), for the proper function of the plants stomatal openings. Through the utilization of these two elements, the plant is able to control its internal water balance.

That is not the only role which chloride plays in plants. It also plays a very important part in photosynthesis, particularly in helping to control the hydrolysis process. It also aids in the process of cation balance as well as the transport of ions and nutrients throughout the plant system. There is even some research that shows Cl can lessen the effects of fungal infections in a way that hasn’t yet been defined. Research continues to be done on the role of chloride in plant growth. ­­Some people speculate that Cl actually competes with nitrate uptake tending to promote the use of ammonium nitrate. This could explain the possible role that Cl takes in the suppression of some plant diseases because high plant nitrates have a strong association with the seriousness of plant diseases. The higher the amount of nitrates, the more likely that plant disease could be expected to be.

The most common compound of chlorine, sodium chloride (common salt), has been known since ancient times. Around 1630, chlorine gas was first synthesized in a chemical reaction, but not recognized as a fundamentally important substance. Carl Wilhelm Scheele wrote a description of chlorine gas in 1774, supposing it to be an oxide of a new element. In 1809, chemists suggested that the gas might be a pure element, and this was confirmed by Sir Humphry Davy in 1810, who named it from Ancient Greek: χλωρός khlôros “pale green”.