University of Maryland Extension

Chlorine Toxicity

chlorine damage on dogwood

Excess Chlorine

  • Scorched leaves may be the result of chlorine toxicity.
  • Chlorine is a micronutrient, essential to plant growth. However, too much chlorine can accumulate in leaf tissue, resulting in leaves with a scorched or burned appearance.
  • Trees with scorched leaves have brown or dead tissue on the tips, margins, or between the veins of the leaf. Leaf tissue may appear bleached, instead of scorched.
  • Leaves may be smaller than usual. They may yellow and drop early.
  • Chlorine toxicity can result from air pollution, in the form of chlorine gas, or from excess chloride in the soil.

How do plants become exposed to chloride?

  • Chlorine (Cl) converts to chloride (Cl-) in the soil and is absorbed by plants in this form.
  • Excess chloride can build up in the soil from swimming pool runoff, irrigation water, or excess soil salts (sodium chloride).
  • Chloride toxicity is most common in irrigated, dry regions, seacoast areas, and near roads frequently treated with salt in the wintertime. 
  • Damage to plants from chlorine gas is less common than damage from other air pollutants, such as sulfur dioxide, fluoride, and ozone.
  • Chlorine gas is a by-product in the manufacture or incineration of glass, plastics, paints, and stains. It is released from refineries or as a result of chemical spills.
  • Reducing air pollution at its source is the best solution to reduce damage to plants and people. Careful watering practices can reduce air pollution damage to plants.
  • Soil should be dry during periods of exposure to air pollutants, followed by thorough watering after exposure.
  • Wetting the leaves of sensitive plants may help to reduce damage during periods of poor air quality.
  • Trees sensitive to chlorine are ash, boxelder, Siberian crabapple, dogwood, horse-chestnut, silver maple, sugar maple, pin oak, sweet gum, and yellow-wood.


  • Chloride levels can be reduced with the use of gypsum. Incorporate gypsum into the soil at a rate of about 50 lbs. per 1000 square feet, in loam soils. Less gypsum is needed in sandy soils, more in heavy clay soils.
  • Water thoroughly to leach toxic levels of chlorine from the soil. 

Rev. 2020

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