Burned Leaf Tips and Leaf Margins (edges)

Tip Burn/ Necrotic Margins

Plants with brown tips and/or leaf margins have been known to generate considerable debate, perhaps because of multiple causal possibilities - you think? ;o) Dry air, over-fertilizing, air pollution, fluoride, chlorine - all have been judged guilty, alongside of bad plants, bad culture, bad water, bad air, bad temperatures, ad infinitum.

Lets think about this - First, we need to consider it a symptom, and not a disease or pest. Like a rash, it could be caused by a wide array of maladies; and like a rash, if we want to get to the offending cause, we need to do tests or become detectives. I can tell you this - there technically is no cure (dead tissue cannot be brought back to life), but you can halt progression in most cases, by looking to cultural causes.

I see fluoride often blamed for scorch in plants like spider plant, Easter lily, maranta, dracaena …. and a few plants are actually somewhat susceptible to leaf scorch injury from fluoride, but not to the degree for which it’s blamed, and we really cant avoid it anyway - it’s all around us - in the water we irrigate with, in superphosphate (a nutrient added to soils), peat moss and perlite as well. Coffee and tea, tea being the greater offender, are reliable sources of fluoride too, so consider that the next time you read that it’s a good thing to add them to your plants.

I wish that tip burn could be so often attributed to Fluoride toxicity, because it would be easy to fix. Adding one teaspoon of gypsum or two teaspoons of dolomite (garden lime) to a six-inch pot of soil raises Ph and makes the fluoride less available for uptake.

If I had to pick a plant most often named as the victim of fluoride it would be the spider plant (Chiorophytum comosum). Most growers think brown tips come with the plant. ;o) At the Soil and Plant Lab in Santa Ana, CA, new spider plantlets were subjected to a barrage of treatments in multiple grow mediums. Included were heavy fertilization with superphosphate, and fluorine applications in irrigation water at 3 times the concentration of what is normally in drinking water. None produced any measurable amount of tip burn, and the short of the conclusions is that many of the injuries previously blamed on fluoride would more accurately have been blamed on other, unfavorable cultural conditions.

Some growers have decided/concluded that fluoride damage is a perlite-related problem and have suggested rinsing it in clear water prior to using it in soil mixes. But testing information still strongly suggests you can't blame leaf scorch on only perlite or fluoride.

The most likely cause of tip burn is an accumulation of metal (fertilizer) salts in soils. Briefly, high levels of salts in soil solutions inhibit the osmotic process, making it difficult, or in some cases impossible for the plants to take up water and dissolved nutrients. When this occurs, distal plant parts suffer tissue necrosis due to salt induced drought stress.

Over-fertilization and softened water are big offenders. When water is too hard, the standard treatment to “soften” it, is to replace the calcium ions with sodium, which is essentially what table salt is. You can replace the calcium and neutralize the sodium in softened water by adding ½ tsp gypsum in a gallon of warm water & allowing it to sit overnight.

In recent plantings or repots in fortified soils (those w/fertilizer added), microorganisms can make toxic levels of fertilizer immediately available, causing plasmolysis (fertilizer burn) and leaf/tip burn.

Humidity can be to blame. Most houseplants are tropicals, and they prefer humidity in the 60-90% range (most greenhouses operate at around 60% in winter). We usually keep our home humidity levels, when controlled, somewhere around the 30-35% range. Unhumidified homes may often have as low as 10-15% humidity levels, which is lower than the average relative humidity in the earth’s driest deserts. This can be a problem.

Though continued ultra-low humidity can be problematic, an even bigger problem is that rapid drop in humidity when plants are brought indoors as the weather turns cold and the furnace is suddenly employed. This can cause not only tissue necrosis, but loss of blooms and buds, and the shedding of other plant organs, sometimes so severe as to cause the death of the plant.

I know some feel humidity trays are effective at raising humidity in their immediate area, but I tested this theory. I placed a digital hygrometer in the foliage of a bonsai tree about 10 inches above wet pebbles in a large humidity tray. It read only about 4% higher in humidity than the room air. I attribute the lion’s share of this rise to normal moisture loss from the foliage through transpiration.

Misting is also ineffective/inefficient. It only increases humidity for as long as water remains in liquid form. Humidity levels return to normal in a few minutes, as soon as evaporation is complete. Misting can also be counter-productive for two reasons. As dissolved salts from mist water accumulate on plant surfaces, the salt can actually “pull” water from tissues, like salt pulls moisture from a ham, where it is lost to the air via evaporation. Misting also closes plant stoma, often for many hours, which slows transpiration and water movement in the plant. When transpiration is slowed, it is also accompanied by a reduced photosynthesizing ability.

You can also suspect cold injury as a possible cause of tip burn. Many tropical plants can leak bio-compounds from cells at temperatures below 50* or so. Low temperatures can also inhibit photosynthetic ability. The time needed to fully recover normal ability once more favorable temperatures are restored varies by plant, but is often measured in days.

Many other cultural conditions can cause tip burn, too. Leaf shine, dust accumulation, a source of ethylene gas or carbon monoxide, inappropriate pesticides, aerosol propellants (cold), and on and on.

In an overwhelmingly high % of cases, you’ll find tip burn originates with something cultural. Most often it can be attributed to a poor soil that drains slowly and causes drought stress from too much water in the soil and it’s accompanying impediment of root function, or from a poor soil that necessitates the grower water in sips to prevent root rot, the upshot of which is to guarantee the accumulation of soil salts and the plant’s inability to take up water.

Al

Great info as usual Al! I was particularly interested in the part about the role of fluoride--I had always heard that there were some plants that were really sensitive to it so it's interesting to hear that it's more likely to be other things instead.

Al, terrific article, loaded with educational info. on plants health. It's said that to help soften "hard water" from household water. To allow the water sitting in room temp. for a day or so will allow chlorine to evaporate off. Is that true?
Thanks.

Chlorine will dissipate if you let the water sit out. However, many cities are moving toward using chloramine to treat water instead, and it will not go anywhere. Also, chlorine has nothing to do with hard water--hard water is caused by salts and minerals that are in the water, and those won't go anywhere either if you let the water sit out.

Ecrane is correct about the chloramine, but it's not generally much of a problem in soils that allow you to water copiously each time you irrigate. You can neutralize soil alkalinity by adding a little white vinegar to your water (1-2 tbsp per gallon), but can do nothing about the hardness (primarily the Ca and Mg content) short of a RO water treatment system or distilling.

Al

Thanks to both, ecrane3 and tapla.
Kim