Damage to Tropical Plants from the Buildup of Mineral Salts and Fluoride By Paula Szilard Build Up of Mineral Salts We periodically get questions about what water to use on the tropical plants in our homes. The fact is, here in the Denver Metropolitan area municipalities and water providers supply water with levels of dissolved minerals that are potentially toxic to certain plants. If you suspect a plant is suffering from a mineral toxicity, it could be from water, yet it could also be from fertilizer, from the perlite in the mix or even from air pollution. In any event, you cannot determine what is amiss until you contact your local water provider, get a water quality report and determine just what minerals are in your water and whether the symptoms exhibited by your plants match those caused by excess amounts of these minerals. Also, since one of the causes of mineral toxicity is fertilizer, you need to be absolutely sure you are not applying too much. We have all had mineral buildup in the form of crusts around the edges of our pots and even on the surface of the potting mix. This is largely buildup from the minerals in our water and possibly some of our fertilizers. This problem is easy to rectify with regular repotting and thorough cleaning and scraping of pots. All buildup of mineral salts in potting mix is harmful. This is because the plants take up water through a semi-permeable membrane on the roots, but this membrane allows water into the root only if the water has a lower level of dissolved mineral salts than the plant itself. So if the plant has a higher level of dissolved mineral salts than the water in the potting mix, then the water is taken up by the plant. The water always moves to the area of greater concentration. However, if your wet soil has more dissolved minerals than the plant, you have a potential disaster in the making. Water cannot move from an area of higher concentration (the wet mix) to one of lower concentration (the plant). The result: The plant wilts, dries and dies. To the uninitiated, the plant looks as though it hasn’t been watered enough, but in reality the excess dissolved minerals in the potting mix have prevented it from taking up the water. We are used to thinking of our water as being really hard, but I checked with Denver Water some years ago and found that most of the water it supplies is only moderately hard. In fact, water destined to certain areas like Lakewood is soft, so it should not result in a ring around the pot. Whether water is hard or soft depends on where it is originally collected and how much calcium is dissolved in it. Fluoride toxicity in a spider plant Fluoride Fluorides are compounds of fluorine gas which can be harmful to certain tropicals. They cause tip and marginal chlorosis (yellowing) on the leaves, followed by browning and a burned appearance, more commonly in monocots, plants like lilies, which have but a single seed leaf than in dicots, plants which have two seed leaves. Fluoride in concentrations of near or above 1 part per million can induce symptoms over time. It accumulates in the tips of plants and prevents the proper closing of the stomates, openings on the leaf surface which permit gas exchange. In addition to the amount of fluoride naturally dissolved in our water, some providers like Denver Water fluoridate water as a public health measure to prevent dental caries. In this process, Denver Water brings its fluoride level up to .9 part per million, enough to cause harm to some tropical plants. In terms of diagnosis, not all tip burn or mineral salt damage is the result to fluoride injury. A chemical analysis of the affected plant’s leaves showing high fluoride levels would be more definitive, however, it is unlikely that the average plant hobbyist would go to such lengths. Florida growers of tropicals first noticed these symptoms in the early 1970’s, but University of Florida extension and research personnel could make diagnoses only after doing additional research. This showed that the plants suffered from fluoride toxicity resulting from fluoride in water, extensive application of superphosphate fertilizer (1 to 2% fluoride) and perlite, a common additive in peat-based mixes. Perlite is a white puffed popcorn-like mineral containing fluoride. It is added to potting mixes to promote drainage. Some of the peat-based mixes themselves were high in fluoride. As a remedy, researchers at University of Florida’s Agricultural Research Center recommended using irrigation water with no more than .5 parts per million of fluoride. They also found that fluoride uptake levels were greater at lower pH levels (more acidic mixes, below a pH of 6), whereas at the higher pH levels of 6-6.5, in more alkaline mixes, the uptake of fluoride was reduced. Many peat based mixes have pH levels of approximately 5.5-6.5. Researchers suggested keeping pH levels higher by mixing in 5-10 lbs. of dolomitic limestone per cubic yard of soil mix. If plants are already potted, then it might be worthwhile to add very small amounts of hydrated lime periodically and watering it in. Apparently the fluoride combines with the calcium to form calcium fluoride, an insoluble compound that does not damage plants. Most of these recommendations are for the industry. On the relatively smaller scale of the tropical plant hobbyist, some of the following measures might be useful: Consider using distilled water if you have only a few sensitive plants. Use a reverse osmosis water purifier if you have many sensitive plants. Regular water filters do not remove fluoride. For fluoride sensitive plants, consider adding a gritty material, such as sand or very small crushed stones instead of perlite to make a well drained mix. Carefully measure out your fertilizer and follow instructions on the container. Use a fertilizer appropriate for the plant, e.g., a citrus fertilizer for citrus plants. Plants use nutrients in given ratios to one another according to their needs. If the NPK ratios on the fertilizer label don’t match the plants needs, then there might be elements left over which could stay in the soil and become part of a mineral buildup. Repot regularly and thoroughly clean pots to get rid of mineral salt buildup. Test the acidity/alkalinity of your planting medium and add small quantities of hydrated lime to pots if necessary to make mix slightly more alkaline. Fluoride Sensitive Plants: Some of the plants below are very sensitive to fluoride. Others are only moderately sensitive. The list below is a composite of lists from two different sources. One listed the degree of sensitivity and the other did not. Also, if you see that one species in a genus is fluoride sensitive, then other plants in that genus might also be. For instance, Chlorophytum comosum, the common spider plant is highly affected by fluorides and if you have Chlorphytum amaniense, the plant with bright orange stems, then it might well share this sensitivity. Aglaonema commutatum ‘Maria’ (Moderate) Asparagus, ornamental (A. densiflorus and others) Aspidistra (Cast Iron Plant) Calathea makoyana (Peacock Plant) (Moderate) Caryota (Fishtail Palm) Chamaedorea elegans (Parlor Palm) (Moderate) Chlorphytum comosum (Spider Plant) (High) Chrysalidocarpus lutescens (Areca Palm) (Moderate) Cordyline terminalis (Ti Plant) (High) Ctenanthe Dipsis lutescens Dracaena demerensis “Warneckii” and “Janet Craig” (High) Dracaena fragrans (Corn Plant)(Moderate) Dracaena marginata (Dragon Tree) Dracaena sanderiana (Ribbon Dracaena) Dracaena thaliaoides (Lance Dracaena) Howea (Kentia Palm) Maranta (Prayer Plant) (High) Rhapis (Slender Lady Palm) Spathophyllum (Peace Lily) Stromanthe amabilis (Dragon Tracks)(Low) Yucca elephantipes (Spineless Yucca)(Low) Zebrina (Wandering Jew) The above discussion deals with mineral build up generally and with fluoride toxicity specifically. A number of other mineral toxicities have been observed and written about—iron toxicity, boron toxicity, and copper toxicity. Perhaps information on these other toxicities will find its way into this newsletter at a later date. References: Chase, A.R. ed. Compendium of Ornamental Foliage Plant Diseases. St. Paul, MN: APS Press, 1987. Blessington, Thomas M. amd Pamela C. Collins. Foliage Plants: Prolonging Quality—Postproduction and Handling: Batavia, IL: Ball publishing, 1993. Conover, C.A. amd R. T. Poole “Fluoride Toxicity of Tropical Foliage Plants” Florists Review, June 13, 1974 p. 23, 59. Griffith, Lynn. Tropical Foliage Disorders: A Ball Guide to Diagnosis and Treatment. Batavia, IL: Ball Publishing, 2002. Griffith, Lynn. Tropical Foliage Plants: A Grower’s Guide. 2nd ed. Batavia, IL: Ball Publishing, 2006. Henley, R. W. “A Review of Fluoride Research on Tropical Foliage Plants.” Florida Foliage Grower 11 (7) July 1974. Rauch, Fred D. “Fluoride Plant Toxicity.” Foliage Digest v. 6, October 1983. p.13-14.

Damage to Tropical Plants from the Buildup of Mineral Salts and Fluoride

Paula Szilard

Build Up of Mineral Salts

We periodically get questions about what water to use on the tropical plants in our homes. The fact is, here in the Denver Metropolitan area municipalities and water providers supply water with levels of dissolved minerals that are potentially toxic to certain plants. If you suspect a plant is suffering from a mineral toxicity, it could be from water, yet it could also be from fertilizer, from the perlite in the mix or even from air pollution. In any event, you cannot determine what is amiss until you contact your local water provider, get a water quality report and determine just what minerals are in your water and whether the symptoms exhibited by your plants match those caused by excess amounts of these minerals. Also, since one of the causes of mineral toxicity is fertilizer, you need to be absolutely sure you are not applying too much.

We have all had mineral buildup in the form of crusts around the edges of our pots and even on the surface of the potting mix. This is largely buildup from the minerals in our water and possibly some of our fertilizers. This problem is easy to rectify with regular repotting and thorough cleaning and scraping of pots.

All buildup of mineral salts in potting mix is harmful. This is because the plants take up water through a semi-permeable membrane on the roots, but this membrane allows water into the root only if the water has a lower level of dissolved mineral salts than the plant itself. So if the plant has a higher level of dissolved mineral salts than the water in the potting mix, then the water is taken up by the plant. The water always moves to the area of greater concentration. However, if your wet soil has more dissolved minerals than the plant, you have a potential disaster in the making. Water cannot move from an area of higher concentration (the wet mix) to one of lower concentration (the plant). The result: The plant wilts, dries and dies. To the uninitiated, the plant looks as though it hasn’t been watered enough, but in reality the excess dissolved minerals in the potting mix have prevented it from taking up the water.

We are used to thinking of our water as being really hard, but I checked with Denver Water some years ago and found that most of the water it supplies is only moderately hard. In fact, water destined to certain areas like Lakewood is soft, so it should not result in a ring around the pot. Whether water is hard or soft depends on where it is originally collected and how much calcium is dissolved in it.

Fluoride toxicity in a spider plant

Fluoride

Fluorides are compounds of fluorine gas which can be harmful to certain tropicals. They cause tip and marginal chlorosis (yellowing) on the leaves, followed by browning and a burned appearance, more commonly in monocots, plants like lilies, which have but a single seed leaf than in dicots, plants which have two seed leaves. Fluoride in concentrations of near or above 1 part per million can induce symptoms over time. It accumulates in the tips of plants and prevents the proper closing of the stomates, openings on the leaf surface which permit gas exchange. In addition to the amount of fluoride naturally dissolved in our water, some providers like Denver Water fluoridate water as a public health measure to prevent dental caries. In this process, Denver Water brings its fluoride level up to .9 part per million, enough to cause harm to some tropical plants.

In terms of diagnosis, not all tip burn or mineral salt damage is the result to fluoride injury. A chemical analysis of the affected plant’s leaves showing high fluoride levels would be more definitive, however, it is unlikely that the average plant hobbyist would go to such lengths.

Florida growers of tropicals first noticed these symptoms in the early 1970’s, but University of Florida extension and research personnel could make diagnoses only after doing additional research. This showed that the plants suffered from fluoride toxicity resulting from fluoride in water, extensive application of superphosphate fertilizer (1 to 2% fluoride) and perlite, a common additive in peat-based mixes. Perlite is a white puffed popcorn-like mineral containing fluoride. It is added to potting mixes to promote drainage. Some of the peat-based mixes themselves were high in fluoride.

As a remedy, researchers at University of Florida’s Agricultural Research Center recommended using irrigation water with no more than .5 parts per million of fluoride. They also found that fluoride uptake levels were greater at lower pH levels (more acidic mixes, below a pH of 6), whereas at the higher pH levels of 6-6.5, in more alkaline mixes, the uptake of fluoride was reduced. Many peat based mixes have pH levels of approximately 5.5-6.5. Researchers suggested keeping pH levels higher by mixing in 5-10 lbs. of dolomitic limestone per cubic yard of soil mix. If plants are already potted, then it might be worthwhile to add very small amounts of hydrated lime periodically and watering it in. Apparently the fluoride combines with the calcium to form calcium fluoride, an insoluble compound that does not damage plants.

Most of these recommendations are for the industry. On the relatively smaller scale of the tropical plant hobbyist, some of the following measures might be useful:

Consider using distilled water if you have only a few sensitive plants.

Use a reverse osmosis water purifier if you have many sensitive plants. Regular water filters do not remove fluoride.

For fluoride sensitive plants, consider adding a gritty material, such as sand or very small crushed stones instead of perlite to make a well drained mix.

Carefully measure out your fertilizer and follow instructions on the container.

Use a fertilizer appropriate for the plant, e.g., a citrus fertilizer for citrus plants. Plants use nutrients in given ratios to one another according to their needs. If the NPK ratios on the fertilizer label don’t match the plants needs, then there might be elements left over which could stay in the soil and become part of a mineral buildup.

Repot regularly and thoroughly clean pots to get rid of mineral salt buildup.

Test the acidity/alkalinity of your planting medium and add small quantities of hydrated lime to pots if necessary to make mix slightly more alkaline.

Fluoride Sensitive Plants:

Some of the plants below are very sensitive to fluoride. Others are only moderately sensitive. The list below is a composite of lists from two different sources. One listed the degree of sensitivity and the other did not. Also, if you see that one species in a genus is fluoride sensitive, then other plants in that genus might also be. For instance, Chlorophytum comosum, the common spider plant is highly affected by fluorides and if you have Chlorphytum amaniense, the plant with bright orange stems, then it might well share this sensitivity.

Aglaonema commutatum ‘Maria’ (Moderate)

Asparagus, ornamental (A. densiflorus and others)

Aspidistra (Cast Iron Plant)

Calathea makoyana (Peacock Plant) (Moderate)

Caryota (Fishtail Palm)

Chamaedorea elegans (Parlor Palm) (Moderate)

Chlorphytum comosum (Spider Plant) (High)

Chrysalidocarpus lutescens (Areca Palm) (Moderate)

Cordyline terminalis (Ti Plant) (High)

Ctenanthe

Dipsis lutescens

Dracaena demerensis “Warneckii” and “Janet Craig” (High)

Dracaena fragrans (Corn Plant)(Moderate)

Dracaena marginata (Dragon Tree)

Dracaena sanderiana (Ribbon Dracaena)

Dracaena thaliaoides (Lance Dracaena)

Howea (Kentia Palm)

Maranta (Prayer Plant) (High)

Rhapis (Slender Lady Palm)

Spathophyllum (Peace Lily)

Stromanthe amabilis (Dragon Tracks)(Low)

Yucca elephantipes (Spineless Yucca)(Low)

Zebrina (Wandering Jew)

The above discussion deals with mineral build up generally and with fluoride toxicity specifically. A number of other mineral toxicities have been observed and written about—iron toxicity, boron toxicity, and copper toxicity. Perhaps information on these other toxicities will find its way into this newsletter at a later date.

References:

Chase, A.R. ed. Compendium of Ornamental Foliage Plant Diseases. St. Paul, MN: APS Press, 1987.

Blessington, Thomas M. amd Pamela C. Collins. Foliage Plants: Prolonging Quality—Postproduction and Handling: Batavia, IL: Ball publishing, 1993.

Conover, C.A. amd R. T. Poole “Fluoride Toxicity of Tropical Foliage Plants” Florists Review, June 13, 1974 p. 23, 59.

Griffith, Lynn. Tropical Foliage Disorders: A Ball Guide to Diagnosis and Treatment. Batavia, IL: Ball Publishing, 2002.

Griffith, Lynn. Tropical Foliage Plants: A Grower’s Guide. 2nd ed. Batavia, IL: Ball Publishing, 2006.

Henley, R. W. “A Review of Fluoride Research on Tropical Foliage Plants.” Florida Foliage Grower 11 (7) July 1974.

Rauch, Fred D. “Fluoride Plant Toxicity.” Foliage Digest v. 6, October 1983. p.13-14.