From an article by
George (Doc) and Kay Abraham
to The Perlite Institute
Gardeners are usually calm, peaceful people, not given to heated argument. After all, a good gardener grows healthy plants and, therefore, doesn’t have to defend his methods. But even the most genteel plant lover can be moved to rage by an ailment without a clear-cut cause. And so plants with brown tips to their leaves have been known to generate considerable debate. Leaf scorch, it seems, has so many causes that it invites expert disagreement.
Dry air is often accused. Over fertilizing is blamed now and then. Air pollution is sometimes suspected and fluoride is occasionally judged guilty of damaging plant foliage. Bad plants, bad culture, bad water, bad air, bad temperatures and humidity all seem capable of browning the edge of a leaf. And since a browned leaf, can’t explain why it is suffering, lots of people offer lots of guesses.
Most of the confusion arises because leaf scorch is a symptom, not a disease or pest. And, like a limp, it can be caused by anything from a broken bone to a tight shoe. The only way to know its true cause is to take the shoe off and x-ray the leg in question.
Everyone knows what leaf scorch looks like. The tips or margins of a plant’s foliage turn brown. The malady may stop at the edges of the leaves or it may spread slowly and, in the end, cause them to drop off the plant. The cure? There really is none. Brown plant tissue is dead plant tissue (if you cut back the brown part, you’ll still get a brown band of leaf at the point where you make the cut). The only real cure is to figure out the cause of the scorch and adjust your cultural practices accordingly.
Within the last three or four years, the house plant world has entertained scores of rumors about the effect of fluoride on plants. This common substance has been accused of damage and death far beyond the powers of most herbicides. And a. few plants, such as Easter lilies, dracaenas, spider plants and marantas actually have been proven susceptible to leaf scorch injury from too much fluoride in their soil.
But fluoride is too often an easy scapegoat for the frustrated grower. It doesn’t cause nearly as much trouble as it is thought to and it can’t really be avoided anyway. Fluoride is every where. There’s so much of it surrounding us that it’s a wonder tooth decay hasn’t disappeared from the earth. It’s not only in the water we use on our plants, it’s in supers phosphate, peat moss and Perlite as well. There’s also fluoride in the air you breathe and the coffee and tea you drink.
In fact, it’s a shame that fluoride isn’t responsible for tip burn more of ten. Fluoride damage is relatively easy to avoid. To counteract the availability of fluoride to plant roots, all you have to do is “sweeten” the soil (raise its pH). Add one teaspoon of gypsum or two teaspoons of limestone to a six-inch pot of soil. Or you can add dolomite limestone to a batch of potting soil at a rate of 2-10 kg pr. m3. These liming materials raise the soil pH into a neutral range where the effects of fluoride aren’t damaging. It’s that simple.
The classic plant to show tip injury and the one most often reputed to suffer from fluoride is the spider plant (Chiorophytum comosum). Many growers feel that brown tips are part of its normal growth. They’ve long been a problem for both commercial and home growers, whether or not large quantities of Perlite and peat moss are used in their soils or super-phosphate is used as a fertilizer.
In 1977, at an independent commercial testing operation (the Soil and Plant Lab, Santa Ana, California), spider plants were subjected to eight carefully controlled growing programs. Fresh plantlets were grown in various growing media: Canadian sphagnum peat moss, calcined clay (Turf ace), Perlite, etc. Some of the plants were heavily fertilized with super phosphate. None of the eight special treatments produced any measurable amount of tip burn, even when water was fortified with three parts per million fluoride (compared to the one ppm normally used in public water systems to help prevent tooth decay). The studies concluded that many of the injuries previously attributed to fluoride probably were due to unfavorable cultural conditions.
Other studies have concluded that fluoride damage is a Perlite-related problem and have recommended that you rinse the soil additive in clear water prior to using it in soil mixes. But in light of the available information from testing, you can’t blame leaf scorch on Perlite, or fluoride, alone.
Incidentally, if you want to try to induce fluoride damage just to prove to yourself that it can happen, pour your morning coffee or tea (after it has cooled) on your plants’ soil. Coffee contains about five times more fluoride than drinking water and tea has even far more than that.
Is Salt Bad?
Plant foods are sold as salts or as salts dissolved in water. Salts are stable compounds that, when dissolved in water, can be absorbed by plants. Fertilizer solutions that aren’t taken up by a plant often dry out and so revert to their salty forms. Because salts “burn” plants, they often are accused of causing tip burn.
Excess fertilizing can cause brown leaf tips. Unused salts build up in over fertilized soil and damage a plant’s roots. This malady can occur even if you fertilize only now and then. If you use too much fertilizer at one time, it won’t all be absorbed. Worse, a sick or dormant plant isn’t able to absorb even, a normal dose of plant food. So feeding a sick plant can harm it. Root hairs that are surrounded by excess salts are injured and, therefore, aren’t able to send water up to the plant. The result: the leaf tips dry up and turn brown.
It’s possible to unintentionally over-fertilize a healthy plant. Some potting soils are fortified with plant foods. Since they contain organic constituents as well, they heat up inside the bag during storage. The work of microorganisms causes the release of extra nutrients and, when plants are potted up, they may get a double dose of fertilizers.
Plants potted with unfortified soil and fed only at proper intervals still can get tip burn from fertilizer. When dry soil is fertilized, roots suddenly are exposed to a very high concentration of nutrients. Clay pots all too often show another kind of salt build-up. The white crust that accumulates on the out-sides of pots is mostly fertilizer (that passes through the porous sides) and partly hard water solids. As far as has been determined, the salts that collect from hard water do not burn roots or cause plant injury except to acid. loving plants such as azaleas.
How About Dry Air ?
Most tropical plants like high relative humidity, from 60 to 90%. Most, however, grow well at humidity’s around 50%, close to the healthiest humidity for people, about 35%. But the air within a centrally heated home can dip below 15% during the winter. This actually is about 10% lower than the average summertime humidity in the Sahara Desert and can be. very rough on both plants and people.
Greenhouse humidifies average close to the 60% that so many plants seem to like. When these same plants are introduced into your home, the shock of low humidity causes their leaves to turn brown around the edges. In addition, they may drop flowers and buds. Some plants never recover from the shock.
That’s why people make and use pebble trays. A pebble tray may be nothing more than an old ice-cube tray or plastic dish filled with pebbles and water. Misting foliage several times daily increases humidity temporarily, but in very dry homes it may not make much difference. If your home is quite dry, group your plants together as a last resort in the battle against low humidity.
Could It Be the Cold ?
A number of tropical plants are injured when subjected to cool ( 4-7ºC) temperatures or watered with cold water. Plants particularly susceptible to harm caused by low temperatures include aglaonemas, dieffenbachias and fittonias. Symptoms such as brown spots on leaves and leaf edges can be seen on chilled African violets, philodendrons, syngoniums and sansevierias.
To a plant, a cold windowpane can seem like a huge chunk of ice. Any cold window creates, in effect, a draft. Air cooled by the window becomes heavy and settles, passing by your plants as it goes. Drawing the drapes between glass and plants is one remedy.
Other Tip Burners
Plant shine compounds may enhance foliar appearance a great deal. But too much shine can reduce a leaf’s ability to photosynthesize and may injure its growth. The injury starts, of course, at the leaf tips. If you apply these compounds to keep dust away, be sure to follow the instructions on the product label.
In urban areas, dust is a major problem. Unseen pollutants are even worse. Ethylene, carbon monoxide, sulfur dioxide and several other air-borne pollutants can be damaging to green growth. Plants growing on city windowsills or near carports are especially susceptible to these woes. Unfortunately, the symptoms of pollution damage are the same as those of other problems and the cures (moving to the country and twice daily showers) are impractical.
One plant’s medicine may be another plant’s pollutant. Don’t use a farm or garden pesticide on a houseplant. And don’t hold an aerosol spray can too close to a plant. The gas propellant rushing out is so cold it can freeze plant tissue and produce a scorched tip or two in no time, the same kind of injury you’d receive if you touched dry ice.
Properly used houseplant pesticides are dangerous when used on the wrong plant. Malathion is injurious to crassulas (jade plants), poinsettias, asparagus ferns, maidenhair ferns and gloxinias. A fungicide containing benomyl can cause leaf tip injury to Swedish ivies, scheffleras and annual seedlings.
Something just as subtle as tip burn caused by chemicals is sudden tip burn that seems to. show up on a healthy plant almost overnight. It may have. A pet cat may be on the prowl, attacking such feline favorites as ferns, spider plants and dracaenas. Plants growing in crowded passageways may be getting their bumps from passing guests. Brown tips are their signal that it’s time to give them more elbowroom.
Also Around The House
A common practice for eradicating soil pests is to pour on household bleach. This is a fine, inexpensive way to kill underground villains but it also can be a way to cause chlorine burn. If your drinking water comes from a well, there should be no problem. But if you use highly chlorinated city water, the addition of bleach can produce not only leaf scorch but also death.
City dwellers who want to try the bleach remedy first should let the water sit overnight so that the chlorine can dissipate. Then, to make the soil drench, add the usually, recommended dosage of one tablespoon of house hold bleach to one quart of water.
And what about water that has been run through a softener? When water is too hard, the standard treatment is to replace the calcium ions with sodium, the main ingredient of table salt. You can replace the calcium and neutralize the sodium in softened water by drawing off a pail of the stuff and adding one-teaspoon of gypsum. Our opinion, however, is that if it’s safe for people, it’s safe for plants. Al- though the same ‘kind of salt kills roadside trees when it’s spread across wintry streets, we’ve heard reports on both the good and bad effects of soft water on house plants.
Tip burn can be caused by. a number of things. But, more often than not, it is the result of bad cultural habits, not outside influences such as pollutants, fluoride in the water or poor soil content. If your plants suffer from this symptom, change the way they live. Generally speaking, you can remedy the problem without ever understanding what caused it. Just make a few common sense improvements in the way you grow your afflicted plants and they almost certainly will stop turning brown at their edges.