Some houseplants are sensitive to the fluoride that is added to municipal tap water for the purpose of preventing tooth decay in humans.
The symptom of fluoride toxicity in plants is leaf necrosis (yellowing, then browning, leading to dead, scorched areas on the leaf), which appears mainly at the tips of the leaves and along the margins (edges), spreading inwards. This is typically described as ‘tip burn’.
Fluoride is a cumulative poison in plant leaves, and may accumulate gradually over time. It strongly inhibits photosynthesis and other processes, and moves in the transpiration stream from roots or through stomata (leaf pores) and accumulates in leaf margins (edges).
Once the leaf tips or edges turn brown, the damage is irreversible. Either trim off the affected leaf tips or whole leaves after the damage appears.
Indoor plants that are more susceptible to fluoride toxicity are monocots, including those from the Agave (Agavaceae) family, such as dracaenas, cordylines and yuccas; and the Lily (Liliaceae) family, such as spider plant, and lilies. A more detailed list is provided below.
List of Fluoride Sensitive House Plants
- Calatheas, such as Zebra plant (Calathea zebrina) and others (Calathea spp.), from the Marantaceae family
- Cordylines or Good Luck Plant (Cordyline terminalis) from the Agavaceae family
- Dracaena species, such as Lucky Bamboo (Dracaena sanderiana), Madagascar Dragon Tree (Dracaena marginata), Dracaena ‘Janet Craig’ (Dracaena deremensis ‘Janet Craig’), Dracaena ‘Warneckii’ (Dracaena deremensis ‘Warneckii’), Happy Plant or Corn Plant (Dracaena Massangeana) from the Agavaceae family
- Lilies (Lilium spp.), from the Liliaceae family
- Never-Never Plant (Ctenanthe oppenheimiana), from the Marantaceae family
- Parlor Palm (Chamaedorea elegans), from the Palmae family
- Peace Lily and others (Spathiphyllum spp.), from the Araceae family
- Prayer Plant (Maranta leuconeura), from the Marantaceae family
- Spider Plant (Chlorophytum comosum), from the Liliaceae family
- Tahitian Bridal Veil (Gibasis pellucida), from the Commelinaceae family
- Yuccas (Yucca spp.), from the Agavaceae family
Other Factors That Can Cause Indoor Plant Leaf Tip Burn
The presence of leaf tip burn doesn’t always indicate a fluoride toxicity problem. It is important to note that other factors can also cause tip burn in indoor plants, and these include:
- Improper watering – too little, too much or inconsistent watering
- low humidity levels
- exposure to hot dry air – from heating ducts
- inappropriate light – insufficient light or leaf scorch from excessive sunlight though a window
- inappropriate temperature – too cold or too hot
- buildup of salts or fertiliser in the growing medium
How to Prevent House Plant Fluoride Toxicity
There is no easy way to remove fluoride from tap water. Instead we can use the following options to reduce the problem of fluoride injury and toxicity in fluorine-sensitive indoor plants:
- Water plants with straight rain water, or tap water diluted with rain water. It’s also possible to use distilled water, but it’s not easy to source it cheaply enough for indoor plant use.
- Avoid potting mixes that have a high percentage of perlite, as this heat-expanded natural mineral, which is used to increase drainage and porosity, does contain some fluoride.
- Do not use fertilisers which contains superphosphate, since it often has high levels of fluoride, enough to cause foliar burn on sensitive plants.
- Keep the pH of the potting mix at approximately 6.5-6.8 and/or increase calcium levels to precipitate the fluoride out of solution, this will chemically bind it up to make it unavailable for plant uptake.
(Note – a good potting mix will have a pH close to neutral (7.0), and a decent balanced fertiliser will have sufficient quantities of the secondary macronutrient calcium, so there’s no need to mess with either of these when using quality growing media and fertilisers!)
Generally, fluoride in the soil or growing medium is not available to plants to take up. Roots take up small amounts of soil fluoride by diffusion, which results in a low concentration in the plant leaves. Inorganic fluorides usually only remain in solution (as fluoride F- ions) that are available to plants under conditions of relatively low soil pH (acidic conditions) and low hardness (low calcium levels).
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References
- Clemson University Cooperative Extension Service, Houseplant Diseases & Disorders Factsheet HGIC 2251 Updated: Sep 10, 2021, https://hgic.clemson.edu/factsheet/houseplant-diseases-disorders/
- University of Tennessee, Tennessee Master Gardener Handbook, Chapter 13, Houseplants, https://extension.tennessee.edu/MasterGardener/DocumentsAgentResources/Houseplants/Instructor_Chapter_PDF_(2011)_Houseplants.pdf
- Virginia Cooperative Extension, Piedmont Master Gardeners, PMG News, Houseplants With Brown Leaf Tips, January 19, 2022, https://piedmontmastergardeners.org/houseplants-with-brown-leaf-tips/
- Fluoride toxicity in plants irrigated with city water, Heidi Wollaeger, Michigan State University Extension – February 20, 2015, https://www.canr.msu.edu/news/fluoride_toxicity_in_plants_irrigated_with_city_wat
- Pacific Northwest Extension, Plant Disease Management Handbook, Fluorine Toxicity in Plants, Jay W. Pscheidt, Fluorine Toxicity in Plants, http://pnwhandbooks.org/plantdisease/pathogen-articles/nonpathogenic-phenomena/fluorine-toxicity-plants