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Re: leaf burn causes?

  • Subject: Re: leaf burn causes?
  • From: Steve Marak <samarak@gizmoworks.com>
  • Date: Sun, 30 Nov 2014 11:33:28 -0600

I'll add a couple of comments to Ted's excellent note on water quality.

Even with relatively good water - low in dissolved salts - there is a lot of difference in how salts will build up in medium on a greenhouse bench, where leaching water can run straight through the pot and carry salts with it, compared with the same pot in a tray or saucer or other place where water is held at the bottom of the pot (and the medium inside) until it evaporates.

I keep a very few plants on a windowsill at my office, so they're in a tray. Even though I use only deionized water, which has essentially no dissolved salts, salts that dissolve from the medium itself, plus salts in the fertilizer I use periodically, have nowhere to go and so build up in the tray. With the next watering those deposits will redissolve to whatever extent their solubility allows and can produce surprisingly high TDS values relatively quickly, and if the pot sits flush in the tray that solution permeates the bottom of the medium. Since I'm lazy about repotting, I wash out the tray every few weeks and periodically flush the pots in a sink.

Also, some media are widely considered to "hold" salts from water and fertilizer better than others, and so need replacing more often. I haven't seen any rigorous measurement, so take this with a grain of (undissolved) salt, but I know orchid growers who believe that sphagnum moss must be replaced as often as every six months if you are feeding regularly.

Some water supplies are switching from chlorine to chloramine as a disinfectant, because it's more stable and thus is effective longer. But that also means you can't get rid of it just by letting the water stand for a day or two - it requires special treatment. As usual  - think fluoride - there is a lot of debate over the safety and desirability of chloramine. I haven't seen any reports of plant toxicity, but I know there are aquarium enthusiasts who have had big losses when their water supply switched to chloramine. (Chlorine is toxic to fish too, just easier to remove.)

Note also that very pure water, which has a theoretical pH of 7.0 dead on, if left exposed to the air will quickly become somewhat acidic as gaseous acid anhydrides from the air, mostly carbon dioxide, dissolve into it. What the value will be when equilibrium is reached depends on what's in your air, but for typical levels of carbon dioxide the theoretical pH is 5.6-5.7 - and indeed when I measure rain water here (northwest Arkansas), it's pretty close to that. That's 100 to 1000 times as acidic as our tap water, which like Ted's is adjusted up into the 8-9 range. Surprisingly, to me anyway, most plants don't seem to mind the higher pH of tap water, but we switched to reverse osmosis water in the greenhouse, and our unscientific observation is that the plants grow better.

Steve


On 11/29/2014 2:50 PM, Theodore Held wrote:
Just for information purposes, I exist on city water here and it is fluoridated. Most municipal waters in the United States have small amounts of soluble fluoride. Large amounts can, indeed, be toxic. But the rules for fluoridation keep the level quite low and it should be safe (see my comment on salt buildup, later). As I mentioned previously, my experience here is that the leaf tip burn goes away with sufficient moisture and my practice to keep them moist uses only plain tap water. Most municipal waters in the U. S. also contain a small amount of chlorine as a disinfectant. The chlorine dissipates quickly upon sitting (overnight). I also have chlorine in my trap water.
 
Recall also that all (almost all?) municipal water sources are also lightly alkaline, meaning a pH in the range of 8 or 9. The reason for that is to minimize water pipe corrosion. This also applies to my water supply, which originates from the Great Lakes.
 
One problem that people sometimes have is keeping their plantings for extended periods without refreshing the soil (whatever the composition). If tap water (or well water) is added from time to time (except for deionized or distilled water, from which no salts will originate) salts gradually build and can lead to "burn" phenomena. The kind and extent of dissolved salts in your water can be seen by evaporating some of it in a clean glass vessel. Look for the milky white residuals. These are salts. Water used to keep plants wet will transpire through the leaves and evaporate from the soil, but any salts will be left behind. To some extent excess salts can be purged with leaching and subsequent disposal of the leachate. People often ask me about the "calculus" of whitish salt that appears on pot rims over time. This is mostly calcium sulfate (gypsum). It is diagnostic of an accumulation of salts in the potting medium, although the calc is not soluble in new added water. Fluoride used to treat tap water is a typical salt and is not volatile. It also gets converted in horticulture to a very insoluble form (as calcium fluoride), meaning that it will not be flushed with a leaching. That means fluoride will accumulate as a planting ages without periodic refreshing of the planting mix. (My guess is that since calcium fluoride is so insoluble it must be essentially inert once created.)
 
Finally, it should go without saying that once tip burn occurs it will not go away. Brown tips are dead tissue. Success with any remedy will need to be noted on new leaves as they appear. If you are successful the new leaves will stay green while the affected leaves will stay with their brown tips. If you have a big display of Spaths, it might take a couple of years or more of better growing conditions to finally have a planting without brown tips, as old leaves die off and are replaced by nice green ones.
 
Ted Held
Detroit.

On Thu, Nov 27, 2014 at 4:27 AM, Ferenc Lengyel <feri.lengyel@gmail.com> wrote:
Dear Derek,

I have read about the fluoride issue, but our tap water has a pH somewhere between 8.0 and 9.0 and I have not tried to raise the pH any further. What is more, using distilled water and sometimes acidifying it seems to eliminate the problem. So I am really confused.

Ferenc

On Wed, Nov 26, 2014 at 1:52 AM, derek burch <dburch23@bellsouth.net> wrote:

Definitely keep thinking of Fluoride in your city water. It has ruined many crops of the leafy aroids for nurserymen all over the place. And the person who mentioned the raising pH to help the situation is definitely right. I used to find in nurseries that the plants that remained in one size pot would show symptoms as the media gradually acidified.

 

Derek

 


From: aroid-l-bounces@www.gizmoworks.com [mailto:aroid-l-bounces@www.gizmoworks.com] On Behalf Of Theodore Held
Sent: Tuesday, November 11, 2014 12:42 PM
To: Discussion of aroids
Subject: Re: [Aroid-l] leaf burn causes?

 

Ferenc,

 

I am probably not the best person to answer your inquiry. But seeing no responses as yet, maybe my words will induce the more knowledgeable members to chime in.

 

I stopped my Spathes from experiencing leaf tip burn by taking the advice of the late Steve Lucas who indicated to me that he grew his in an almost swamp-like aquatic planting, with the roots continuously wet (that is, soaking in a puddle of standing water). Once I tried his technique all my new leaves stopped having tip burn and they continue to be fully green to this day (five years now). My water is pretty good, being relatively low in conductivity and moderately alkaline pH (in accord with desired municipal practice). I do not fuss with mixtures with DI water or trying to modify the pH.

 

One factor you might consider would be the relative humidity of the surrounding air. Assuming that wet feet would not be desired for many species, having a low relative humidity might put stress on leaf tips on those varieties with more normal water likes. This might also account for your seeming success at work with problems at home. Just a suggestion.

 

I also grow Anubias, but mainly in a submerged state. I never have any sign of abnormal necrosis with these. When I have grown them with leaves emergent I have also never had and tip burn or abnormal necrosis. This one is a mystery to me. I also would not exclude the possibility of disease.

 

Other factors that might be in play are those involved with horticulture taken as a whole: light level, air movement, temperature, environmental variables such as day-night fluctuations. My advice would be to take notes on anything you might think about and compare the environment where you are successful to where you are not.

 

Ted Held

Detroit.

 

On Sun, Nov 9, 2014 at 2:40 PM, Ferenc Lengyel <feri.lengyel@gmail.com> wrote:

Dear Aroiders,

 

I know that this question is not aroid specific but I know no other forums where I could ask it (and it incudes aroids).

Does anybody know what physiological difference might cause leaf tip in some aroids, but not in others? I have some Philodendrons, a Dieffenbachia cultivar, two different Syngoniums, a Spathiphyllum cultivar, Epipremnum aureum, an Aglaonema and Monstera deliciosa (I had another Monstera with small leaves, but it has died). Of these genera, Monstera, Spathiphyllum and Epipremnum aureum shows leaf tip burn (the tip of the leaves becomes necrotic) followed by necrosis of the whole leaf. Monstera deliciosa is a hard plant to kill, but here in my appartment it can not develop normally, the leaves become necrotic. It applies to Epipremnum aureum, another easy houseplant too. The same might be the situation with Spathiphyllum, but I bought it recently and I mainly watered it with deionized water. Lately I gave it tap water and it started to exhibit leaf tip burn too. I had another Monstera which has perished after necrosis of all of its leaves. On the other hand my Philodendrons, Dieffenbachia, Aglaonema and Syngoniums are not affected at all.

In my aquarium I had Anubias plants which suffered from nercosis of their leaves too. They perished (I used 1:1 mixture of tap water and deionized water).

My non-aroid plants suffering from leaf tip burn include Dracaenea fragrans (necrosis is limited to leaf tips) and Chlorophytums. I have Chlorophytum comosum (again a plant nearly impossible to kill) and a Chlorophytum orchidastrum cultivar (’fireflash’). Both suffer of severe necrosis and loose all of their leaves and die when watered with tap water. When I water Chlorophytum with deionized water (once a month or so with citric acid dissolved in it to lower pH) my Chlorophytums do much better. It is interesting as I read that Chlorophytum comosum is sensitive to fluoride and raising the pH of the water (that is the opposite what I do) helps by decreasing solubility of fluoride ions.

My non-aroids not affected include a Vriesea cultivar (I know that bromeliads should not be watered with tap water but recently I started to do so with no problems) and a Schefflera.

Th pH of our tap water is around 8.0 and that of deionized water is around 5.5. Light levels are low but Monstera deliciosa must not die where Philodenrdons live and grow.

The plants do not suffer from a „bad gardener” as at my workplace my Mosteras florished. There lives the motherplant of my M. deliciosa and it is huge, without any leafburns and the small leafed species (which I lost here at home) grew well without any blackening of the leaves too. Sunburn, under- or overwatering, too heavy soil mix should be excluded (maybe it is not the right word... I mean, do not consider them).

Maybe it is not the water, but I can not think of anything else. Monstera deliciosa and Chlorophytum comosum are so easy plants to grow and make thrive that it is really strange that I can not even keep them alive here at home. 

Do you have any idea?

 

Ferenc


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