The commercial product will not be as pure as the lab product, so to prevent clogging the sprayer, you can cut out a piece of cloth from an old T-shirt or under shirt, and place in a funnel to filter out sand and other large particles.

The cloudiness can be solved using filter paper, which I can get for free when I have access to the lab. However, if the solution has been sitting for a while (overnight), the sediments will settle near the bottom, and you can pour out the clear part of the solution.

Gypsum has low solubility in water. To make it dissolve better and faster, you can use boiling water or hot tap water and stir well for the first few minutes. If youÂre really impatient, you can pour about half gallon of hot tap water into a pot with the powder and put on a low boil/simmering with stirring until everything dissolve, then add cold water to bring up to a gallon. ItÂs very stable at high temp (> 1000 C), so donÂt worry about fumes coming off. You can make a lot of the solution at one time to keep in closed container, and use when needed.

IÂd like to hear about your results. Please give update after you try it. YouÂre probably the first here to try. ThatÂs cool!

Michael, your results track my own experience, which is that commercially available ag gypsum, even after days, is not very soluble in water at room temperature. I briefly researched a gypsum injection irrigation system for water quality issues and concluded ag gypsum would clog my irrigation filters.

I suppose for cut flower purposes, the cost of purified calcium sulfate is comparable to any fungicides that would be used instead.

The cloudy suspension is fine enough to pass through coffee filters, which I tried last night, but it did settle overnight so I could pour off nearly clear liquid for the vase.

Michael, the Espoma gypsum is only 68% calcium sulfate. Gypsum is made by treating lime with sulfur dioxide and the product usually has an alkaline pH (pure calcium sulfate should be neutral) and contains things like silica and unreacted lime. I agree that the logical thing to do would be to purchase some pure calcium sulfate but.....don't you really want to develop a convenient method that the average person would actually use? I suspect any soluble calcium salt, dissolved somewhere in the neighborhood of 50mM, will do the job.

One suggestion: Dissolve Aglime (finely powdered limestone, calcium carbonate) in the minimum amount of vinegar to make a solution of calcium acetate. I would add 5 grams (call it 1 tsp) of lime to a glass of water, neutralize with vinegar until the lime just dissolved, then dilute to 1 quart. The solution should be roughly 50mM in calcium. The amount of vinegar required should be about 6 or 7 tbs.

ThatÂs a lot of impurities from Epsoma gypsum! So MichaelÂs solution is well below 50 mM, plus the impurities in the solution may affect the outcomes. Other ag gypsum products may not be that much different. I personally wouldnÂt use those.

One site below sells lab grade pure gypsum. To start out, 500g purchase can make about 16 gal at 50 mM for a price of $16 plus shipping. Is it more cost effective than fungicide or florist preservative?

Note that it costs about 3 times more to get the pure lab product at 500g purchase. It will cost less to buy in larger quantity, but probably not right away.

Here is a link that might be useful: lab grade gypsum

"Espoma Garden Gypsum is the finest grade gypsum available." lol. I see Diamond K brand ag gypsum, for example, is 97% pure.

I mentioned the undissoved grit, which according to what Mike said is probably sand. That wouldn't be a problem except for measuring. Free lime might be a problem in a vase, since acid water is said to promote hydration. That's why the floral preservatives include citric acid. I guess I could roughly measure the sediment % and neutralize the free lime.

Mike, thanks for the lime recipe.

Here's another article where they established the 50mM level of treatment for cut flowers to reduce botrytis. They used both calcium chloride and calcium sulfate. Calcium chloride is another household item, sold as ice-melting salt.

Also they report using calcium nitrate as fertilizer increased the calcium content of flowers.

Here is a link that might be useful: abstract

Roseleaf, I am not a chemist and I have serious difficulty to follow your explanations. I wish I hadn't. Could you, please adjust the language of your contributions so that we - laymen or laywomen - could also utilize it? I would appreciate it so much!

I did go back to the original article Michael provided the link for and I noticed that they mention (barely, but they do mention) calcium nitrate.

"Calcium ions in the form of sulfate (CaSO4), chlorate (CaCl2), or nitrate (CaNO3) are promising in the control of B. cinerea."

Michael's experience was that gypsum does not dissolve too well in water. My experience with calcium nitrate was the opposite when I used it for peppers and tomatoes - it dissolved fast and if I remember well there was no sediment to speak of. So if calcium is the one that is decisive in preventing botrytis and is the promoter of longer vase life maybe it is worth experimenting with it.

I also recall that a couple of years ago someone, maybe Henry Kuska referred to some experiment using calcium nitrate to prevent or cure botrytis. I do not remember an article attached to his referral so I didn't save it as I did with the articles Michael provided link for.

Maybe Mike Rivers could help me to give the Tbs measurements for calcium nitrate. I would be very grateful if he did.

Another question from someone who is illiterate in chemistry. Would soaking rose stems in some kind of calcium solution help to extend the vase life of all roses or only those that have botrytis issues? I would assume after reading the original paper that it should extend vase life in general but I maybe wrong.

Ceterum, I felt the need to include some chem references so someone who had some chemistry knowledge understood how I arrived at my explanation. I donÂt mind to give a version of it w/o the extra details:

Calcium nitrate would work, but that one would use much higher concentration of calcium nitrate in water as compared to calcium sulfate to get similar result from calcium sulfate experiment. And I donÂt know if petals or plant tissues would be damaged when sprayed or soaked at higher concentration than 50 mM. (hope this helps you better)

Organic stores also sell calcium nitrate as fertilizer source for calcium and nitrogen. Perhaps, just following the recommended use of it as garden fertilizer is safe. But you can certainly experiment with it in similar ways as with calcium sulfate.

Michael mentioned good grade gypsum from Diamond K, which IÂve never seen it at local stores. Their products probably are not available in the east coast area. I may have to make a mail order.

"Another question from someone who is illiterate in chemistry. Would soaking rose stems in some kind of calcium solution help to extend the vase life of all roses or only those that have botrytis issues?"

I infer from the article that it would help to extend the life for all cut roses, and help reduce botrytis problem in roses that are susceptible. I would try it on all kind of cut flowers beside roses.

Ceterum, you asked for the amount of calcium nitrate to make a 50mM solution. This should be a simple question but it turns out that there are all sorts of commercial products termed calcium nitrate and the answer would be different for each of them. It appears that the most common calcium nitrate fertilizer is actually a compound which incorporates calcium nitrate, ammonium nitrate and water in molecular ratios of 5:1:10. If the label on your calcium nitrate bag reports 15.5% nitrogen and 19% calcium, then you probably have this stuff and the amounts to use would be:

For a solution which is 50mM in calcium: 2 teaspoons per gallon of water.

For a solution which is 10mM in calcium: 0.4 teaspoon per gallon of water.

You might note that MiracleGro fertilizer has roughly the same nitrogen analysis as calcium nitrate fertilizer and the MiracleGro label specifies concentrations of 1 or 2 tablespoons per gallon. Also, the nitrate form of nitrogen is, I think, supposed to be safer for plants compared to the urea form of nitrogen used in MiracleGro. In other words, I don't think the above concentrations of calcium nitrate will damage your plant tissue or the blossoms - but the only way to know for sure is to try it.

I have to correct the above. Replace "gallon" with "quart" , the recipes are for making a quart of solution. I'm getting old.

I would add a qualifier to Âany calcium solutionÂ: that the overall solution should be close to neutral pH 7 and the non-calcium parts (i.e. nitrate, sulfate, etc.) should not have negative effects on the plant tissues.

The calcium nitrate that I saw was in the form of CaN, with 15% N and 12% Ca, printed on the bag.

I would think that any calcium nitrate fertilizer would work so long as the stuff completely dissolves in water at the indicated concentrations. Percent calcium does not have to be reported on fertilizer labels, but, come to think of it, I'll bet most calcium nitrate fertilizers do report it. If yours does, then just modify my numbers reported for 19% calcium by multiplying by the factor (19 divided by label percent calcium). In other words, if you have a 12% calcium fertilizer, the correct amounts to prepare a solution which is 50 mM in calcium would be:

(2 tsps) x (19/12) = roughly 3 tsps per quart of water

Thanks Mike. I can always understand your explanations and recommendations. You are a treasure and you are indispensable.

Remember, the 50 mM solution is for temporary soaking of stems and the 10-20mM is for spraying buds and upper stems of plants in the garden. I am more interested in the possibility of reducing botrytis in the garden.

The residue in my Espoma gypsum that was (practically speaking) insoluble at room temperature turned out to be a little over 15%. However, the label guarantees 92% gypsum. The Washington State analysis page reported 68% gypsum.

So we conclude garden gypsum isn't the best material to use, but I have some clear gypsum solution. I added a little vinegar and it didn't fizz. Does that mean it doesn't have dissolved free lime?

At low concentration of dissolved lime in the solution you wonÂt see the fizzing action when adding a little or a lot of vinegar. In this case, if we want to avoid adding too much vinegar to tip the solution to the acidic side, we can check the pH before adding vinegar and after with a pH tester (litmus paper or some digital tester equipment).

Is it the same Espoma gypsum you use as shown in this link? It says 68%

Here is a link that might be useful: Espoma gypsum

I am also interested in preventing botrytis in the garden. very nuch so. But I want to avoid cloging the sprayer and I also doubt that we could do 15-20 hours of preparation at any given time.

On the other hand, in this unbearable heat I love to have roses in the house - the more the better and the more they`last the better yet.

The 50mM calcium nitrate solution would be either 8 or 12 TSP/gallon of 15% nitrogen. That's a much stronger solution than you would use as fertilizer. I wonder how it would affect cut flowers. The 10 mM solution should be OK for spraying plants.

Roseleaf, it is the same Espoma brand, but my bag (a couple of years old) incorrectly says 92% gypsum. The 15% undissolved residue is not white like gypsum, but medium gray, maybe a limestone.

Thanks Michael for clarifying. I thought Espoma stopped making higher quality gypsum. I may use a few small samples from the lab to see if I like it before making larger order.

Michael, I was wracking my brain last night trying to come up with a simple way to make a solution of calcium from common houehold ingredients, and then it hit me: egg shells! A quick search online revealed that the average size large egg shell weighs 5.5 grams and contains 2.2 grams of calcium and is at least 95% pure calcium carbonate. A quick calculation revealed that if you dissolve one egg shell with vinegar, dilute the solution to one gallon, you get a 15 mM solution of calcium, exactly what you wanted and how could anything be more convenient? A further search online revealed that dissolving egg shells off of whole eggs is a common 3rd grade science project - you end up with "rubber eggs". Just to check the procedure, I did another quick calculation which revealed that 4 ounces or 1/2 cup of Heinz white vinegar (5% acetic acid) was just enough to dissolve 1 egg shell and convert it all into soluble calcium acetate. So, at about 1:00 am this morning, I added one egg to 1/2 cup of vinegar and watched - and watched - and watched. After an hour, the shell was as stiff as ever. I tried cracking the egg and powdering the shell. Lots of foaming but after an hour, most of the shell was unchanged. I tried heating the mix. After an hour of simmering, maybe half the shell was dissolved, the reaction seemed to be slowing way, way down, and my wife woke up wondering why the house reeked of vinegar. In the end, I decided this is still a simple way to make a calcium solution, provided you can find a 3rd grader who is willing to dissolve your egg shell.

lol, this thread is epic.

Too bad, Mike, the eggshell thing would have been an instant hit with the banana folks.

I wonder if the solution to convenient solution is to put the stuff in a jug in the sun and leave it a few days. I'm trying that. I found that most of the gypsum would dissolve in hot tap water if it is stirred off and on for 20 minutes, but that's still way too much trouble.

Hmm, IÂm not sure if I would delegate that responsibility to a 3rd grader, but itÂs good you tried out in the wee hours of the night Mike :)

So now, the next step is to boil gypsum in a pot to dissolve it a fraction of time compared to hot tap water, even at higher concentration. You need to go all the way Michael, lol. Actually, while reading about calcium sulfate, I found that itÂs also used in food, i.e. making soybean milk to curd by dissolving the powder into boiling milk solution.

OTOH, calcium chloride dissolves extremely fast in water at room temp. It is used as de-icer on roadways, sidewalks, and in food like pickles, bottle water, etc. It absorbs water readily from the air, so must be kept in tight container. At 50 mM, pH is no problem. It can be quite hazardous to someone who doesnÂt handle the chemical properly, so I wouldnÂt recommend it for most home gardeners.

And IÂm back to the gypsum, yeah, the good stuff from Diamond K, which is sold for $14 at 50#. Shipping cost is probably at least as much, but itÂs still dirt cheap at 98% purity compared to 68% of EspomaÂs. And itÂs also fertilizer for lawn and garden.

Here's a study that got good results with calcium chloride in the vase water. They used only 1 mM and 5 mM. The roses stayed in the solution rather than being "pulsed" for 15 hours, but still the 10x/50x difference in recommended concentration-- as opposed to the 50mM calcium sulfate study-- is puzzling. They say a stronger solution promoted wilting. So what's with that?

One thing mentioned in the link is that the calcium-treated cut roses opened faster and larger than controls, as well as lasting longer. Commercial roses are generally cut with the sepals split but not dropped. In my first vase experiment, the gypsum-treated roses did open faster. However, I doubt they are going to last longer. As I said above, I think I clogged them up by not waiting for the fine sediment to settle out.

I have some old calcium chloride. I imagine it is now dihydrate (mol wt. 147) if it wasn't to begin with. Is the danger in the sudden release of heat? Wouldn't using a substantial volume of water diffuse that?

About pH, highly acid vase water (3.5-4) is often recommended. However, one of the calcium sulfate studies mentioned that their spray solutions were as high as pH 12. I presume the vase solution must be alkaline as well.

Here is a link that might be useful: CaCl2

I can think of few factors that account for the vase application of lesser concentration of calcium chloride as compared to calcium sulfate. In molecular weight, there is higher % of calcium in calcium chloride; The dissociation rate of chloride from calcium is higher than sulfate from calcium; Plant tissues become damaged in heavily chlorinated water  this may be the major factor. That may explain the wilting effect at high concentration. And at this low concentration, free form calcium is less (than from calcium sulfate at 50 mM), it makes sense to just leave the stems in the vase and change water solution occasionally. The chloride in it will help reduce bacteria in the solution too. For spraying, the concentration would be even less than vase concentration  it appears not as good option as spraying with calcium sulfate.

"Is the danger in the sudden release of heat? Wouldn't using a substantial volume of water diffuse that?"

Yes to both questions. ItÂs safe to add small amount of calcium chloride to large amount of water, not the other way around unless you want to film a home made explosion scene. Dihydrate form is more stable than anhydrate. ItÂs good to wear rubber glove and donÂt let the stuff get on your skin.

"one of the calcium sulfate studies mentioned that their spray solutions were as high as pH 12. I presume the vase solution must be alkaline as well."

pH 12 is quite basic. I have doubt that a much diluted spray can have that pH, unless there is something else in the water. From what I remember, the pH of calcium sulfate is near 7, and gypsum does not change soil pH.

Here is the passage including the statement that 20 mM calcium sulfate spray solution with polysorbate-20 as a surfactant had pH up to 12. It says high pH on the leaf inhibits the germination of botrytis-- possibly useful information-- in addition to the effect of absorbed calcium on the rose's defenses. This is from the link a few posts from the top.

"Only about 7Â20% of the calcium sprayed on leaves reaches the tissues under the cuticle, whereas most of the calcium stays on the leaf surface (Montealegre and Valdés, 1993). Although, in the present work, no apparent calcium deposit was visible on either leaves or buds after spraying, it is probable that calcium has accumulated on their surfaces. This calcium when re-dissolved in the free water present on the leaf and petal surfaces during the conidium germination phase may have, in some extent, inhibited the production of cutinases and polygalacturonases, which are necessary for penetration and colonization of tissue by the fungus. Besides, the presence of calcium may have increased phylloplane pH values to levels that could have helped to inhibit conidium germination. In pH higher than seven or lower than three, the conidium germination of B. cinerea is drastically reduced (Jarvis, 1977). The calcium concentrations used in this work have generated spraying solutions with pH values up to about 12 as measured in the laboratory. Although no measurements of pH values on the leaf or petal surfaces were taken, it is possible that with the presence of free Ca ions on the phylloplane the pH values have increased to levels that could have affected germination of spores. "

Well, I think I messed up my first trial. I used 2 Tbsp instead of 2 teaspoon of calcium nitrate. (the calcium nitrate I have contains 19 % calcium and 15% nitrogen)

I added more water when I realized the mistake but it is not going to be exact. The stems that were immersed in the solution were darker after 15 hours of soaking.

Next time and when I have enough cut flowers on the same bush to do a control group as well, I will be more careful.

ceterum, this is all misadventures so far :) And I keep running into my own stupid thread on Google.

Savvy folks, when these salts are hydrated, does it affect the volume or just the density?

A manufacturer of calcium nitrate recommends for foliar application 5-8 grams/liter of 19% calcium product. This is the dihydrate at mw 181, so would 5 g/l be a 25 mM solution? I also found an experiment where cowpeas were foliar-fed with 10 mM calcium nitrate. 10 mM would be 1-1/2 TSP/gal according to Mike's calculation, or 1 TB/gallon should be safe to spray.

Calcium chloride is widely used to foliar-feed apples and stone fruits with calcium. However, it is phytotoxic on apple above 81 degrees F, so probably not a good option for spraying roses, as Roseleaf said. If someone wants to try it in vase water, the amount would be around 1/2 TSP/gal for a 3 mM solution to be left in the vase.

Since there is antagonism between calcium uptake and ammonium, potassium, and magnesium, and since rose gardeners tend to oversupply the latter three in the soil, it may be that many roses are slightly undersupplied with calcium.

I'm waiting for you guys to come up with the final formulas. (LOL) It has been a LONGGGGG time since college organic chemistry.
Dawn

"one of the calcium sulfate studies mentioned that their spray solutions were as high as pH 12. I presume the vase solution must be alkaline as well."

So it was the surfactant with the calcium that raised the pH and also helped to keep the liquid sticking to the leaf surface. Calcium absorption into the tissues is limited because of high pH in the spray mists.

From what I see, the experiments presented two different mechanisms to control the fungus with spraying:
1. Use calcium sulfate, and rely on the calcium absorbed to strengthen the tissues to fight the fungus.
2. Use calcium sulfate with polysorbate-20 to raise pH on leaf surface to discourage spore germination, and to allow minimal calcium absorption.

I think the vase solution wouldnÂt have the surfactant as to keep pH close to neutral for better absorption of calcium into the stems and blooms.

"when these salts are hydrated, does it affect the volume or just the density?"

IÂm assuming you referred to the density and volume of a salty solution. When the salt is hydrated, depending on how much water, the salty solution will have new volume and new density. For example, cooking/table salt (sodium chloride, dry) has its own density and occupies some volume. If we dissolve some table salt into a quart of water, the final solution volume will be slightly over a quart and its density will be heavier than water density.

Note that the density of the salt itself (2.16g/cm3, dry form) remains unchanged as it is the intrinsic property of the salt.
"Since there is antagonism between calcium uptake and ammonium, potassium, and magnesium, and since rose gardeners tend to oversupply the latter three in the soil, it may be that many roses are slightly undersupplied with calcium."

I tend to agree with you on this Michael. And to make it worse, hot weather inhibits calcium transported to rose petals, one of the reasons blooms donÂt last long in the heat of summer  I think I read this from the article you posted.

Calcium sulfate looks good to me for spraying while calcium chloride for the vase solution. The major draw back of calcium sulfate is its low solubility. Based on MichaelÂs experiment so far, I would have to boil gypsum to dissolve it faster  not everyone would want to do this.

Michael, 181 is the molecular weight of the monohydrate, not the dihydrate. Doesn't matter, 5g/L of any compound whatsoever which is 19% calcium would have a calcium concentration of 25mM (well, 23.75mM actually, but close enough).

Both the bulk density and the volume will change to some extent when a salt is hydrated. I would just assume any powdered synthetic garden fertilizer has roughly the same density as water and 5 grams of the stuff will be roughly 1 teaspoon.

."I keep running into my own stupid thread on Google." it is not a stupid thread! I am quite excited about the chance to be able to kill botrytis by using a simple, not expensive product. But I would discourage anybody to use 2 tablespoon of calcium nitrate for liter water as I did by mistake. That kills (burns) the cut flowers pretty soon.

"polysorbate-20 as a surfactant" - do you use baby shampoo or there is some other possibility? To buy pure polysorbate-20 online is quite expensive.

Ceterum, when I try spraying gypsum in the garden, I will just try using the minimum liquid detergent to make it spread, as I do with other sprays that don't have a surfactant.

I am not sure polysorbate 20 has anything to do with the experimental results. It is non-ionic, wouldn't that imply a minimal effect on pH?

I am still trying to find a low-hassle way to dissolve gypsum at or above the spray concentration. Also, I messed up my first try with cut flowers and don't currently have enough matchable flowers in the garden to try again with a control. Plus it is so bloody hot in my house, I'd probably have to dip flowers in acrylic to preserve them. Like most people up here, I don't have AC.

No AC? I express my most sincere sympathy!

OK, there is an easy way to dissolve gypsum-- you just have to plan ahead. One TB gypsum in 1 gallon of water, leave in a hot place for a week. This should be suitable for spraying as is or diluted with 1/2 part water. It is easy to pour off the solution without disturbing the coarse sediment.

I used a jug and cool tap water and left it 6 days in the sun. I did shake it lightly several times, which may not be necessary. I made sure the material was spread out on the bottom rather than piled up in a corner of the jug. In cooler weather, it might take two weeks. One could make the jug into a better solar collector by spraying two sides black and turning these toward the sun.

I estimated 1 TB/gal would make a 25 mM solution. About 2/3 of the material dissolved, so the solution should be around 16 mM. In the experiment, they sprayed budding stems with 10 mM and 20 mM calcium sulfate to reduce botrytis petal blight in the flowers. 20 mM was slightly better. One could use this material as base for the fungicide spray every two weeks during the spring flush or whenever a lot of buds are about to open. Or one could spray budding stems separately.

Roseleaf is going to tell us how much a TB of gypsum actually weighs. I would be interested to hear the pH of gypsum solution as well.

So the alternative would be to 'cook' the solution on the stove to dissolve the gypsum?

I think that is Roseleaf's plan, to cook up a concentrated stock solution that would last for a while with dilution. My plan is to fill a couple of jugs and let them sit between sprayings.

About calcium nitrate, you might try spraying at one or two TSP/gallon. I guess in hot weather I'd start with one TSP or spray a test area.

A small bit of information-- Roseleaf suggested the chlorine in calcium chloride (e. g. ice melter) would help to control bacteria and stuff in the vase water. I have a container of calcium chloride + sugar water and one of just sugar water. No flowers in them, but I swished a rose leaf in each. After a week, the plain sugar water is developing a mother, but the sugar water with CaCl2 is still clear.

CaCl2 (1/8 tsp/quart) and sugar makes a very convenient vase solution, but I can't say whether it is as good as 7-up + bleach, or acid + sugar + bleach (or other disinfectant). If plants are sprayed with some form of calcium, then there may not be any value to putting it in the vase.

"If plants are sprayed with some form of calcium, then there may not be any value to putting it in the vase."

Michael, do you mean that the spray destroys the blooms? Did you try to spray?

Or, do you just imply that if they are sprayed in advance, no conditioning is needed with calcium after cutting? I am hoping that the second interpretation is valid.

Sorry for being so dense.

I meant the latter. In one of the studies, spraying the plants with gypsum the day before harvest increased the vase life of cut flowers. I guess spraying a week before harvest would probably help as well. They weren't spraying the petals, since they harvest greenhouse roses before the sepals drop.

I am going to spray gypsum this weekend. Berndoodle wondered if it would damage the flowers. We'll see.

Botrytis stopped all of the buds on our "Ducher" from opening this year. I sprayed the buds with "Neem", because it is supposed to work against all fungus, but I used a foliar strength dilution, and the rosebuds burned. I diluted the Neem a bit more, and it worked perfectly. All of "Duchers" rosebuds are opening, and none were before. I am surprised and grateful.

Luxrosa

Hey, Berndoodle-- what experience was behind your question about spotting the petals?

I did spray gypsum solution 48 hours ago and there are no problems-- a number of blush roses were included.

Any action on this front? I thought we'd hear something from Roseleaf. Has Ceterum tried spraying calcium nitrate?

It seems that gypsum can be sprayed without much trouble or any problems. What if I start spraying the left half of plants only, would that be an effective check? I think calcium must not be very mobile within plants, since calcium deficiency symptoms show in the new growth.

Michel, I didn't spray with calcium nitrate yet.
I could not function in this awful hot and humid weather we had so I kept postponing it. (Or, call me lazy). Then, some day during this week we got a sudden, unexpected but very much welcomed huge storm and several hours of good rain afterwards.

Now most of my roses are not just touched by botrytis but I see rotten blooms all over. Tomorrow I intend to deadhead as much as I could and after that I will start spraying with Calcium nitrate or gypsum if I can find a pure enough one in a nursery.

I still try to figure it out, how and where I could get calcium chloride.... :-)

My flowers have been clean this week after spraying gypsum a week ago. That of course proves nothing whatsoever.

You don't have to use pure gypsum. You just have to figure out what amount of gypsum is being dissolved by whatever dissolving procedures you use. I put in 1 TB. After a week in the heat, there was 1 TSP of grit left after I poured off the solution. Therefore 2 tsp were dissolved in a gallon and that's suitable for spraying.

I guess calcium nitrate would work the same with added fertilizer benefit. I guess fruit growers don't use it because extra nitrogen in the fruit may encourage disease.

Flowers cut two days after spraying with gypsum are lasting better than usual, but no control, so no real evidence.

Possible glitch: after two weeks, my first batch of gypsum solution developed what looks like a bacterial mother, a cloud of whitish filaments. If it is bacteria, I don't know where they are finding the various minerals needed to build their little bodies. Possibly they are reducing the sulfate? I didn't notice a hydrogen sulfide odor-- didn't deliberately sniff though. Do precipitates ever look like this?

Michael, gypsum normally crystallizes as small, needle-like crystals of calcium sulfate dihydrate. If you had a saturated hot solution, cooling would do this.

It looked filamentous, floaty, and whitish in the solution and gooey gray/greenish when filtered out. I didn't touch it or try to redissolve it. It certainly looked biological. However, the solution may have been saturated. I made it in hot water with stirring about 17 days ago, and this morning it had probably cooled to 63 F in the kitchen.

I see the solubility of gypsum given in one place as .3 g/l and another as .21. I think that would be less than 1 TB/gallon at room temperature? So the pulsing solution of 50 mM had to be hot water, even allowing for anhydrous calcium sulfate having more Ca ions per gram?

Michael, I did a little searching online, and the solubility of gypsum at room temperature is about 24 mM and the solubility actually decreases with increasing temperature. If the authors of your paper actually did have a 50 mM solution, it must have been a cold one. Unfortunately, I couldn't find any value for the solubility below room temp.

Thanks, Mike. Do you see anything wrong with the program of getting about 2 TSP actually dissolved in a gallon and spraying it it the garden with, in my case, sulfur? Or other things?
_______
Oh, those pesky decimal places! Good thing I'm not a doctor: "Take 20 aspirin every four hours and get some rest." The solubility by weight is actually 2 or 3 grams/liter, not .2 or .3.

Vase life of flowers that were sprayed with gypsum in the garden 48 hours before cutting-- I bring flowers to work out of water for 20 minutes and put them in plain water without recutting. I am just looking for 4-5 days worth, except from extraordinary keepers like Traviata. Jadis, a 4-5 day rose, lasted 6 days, and the Savoy Hotels are going strong in their 10th day, crisp as can be.

Here is another abstract that got positive results, this time with calcium through the roots in fertigation. But it has to be done apart from other nutrients, so it doesn't seem applicable to the garden.

"The main results and conclusions are: increasing the Ca concentration in the solution from 0.5 up to 5.0 mmol·lÂ1 increased Ca concentration in the flower organs. Susceptibility to B. cinerea decreased with increasing Ca concentration in the solution and was negatively correlated with Ca concentration in the diagnostic leaf and petal. Potassium and magnesium reduced Ca uptake by the rose flower, and increased its susceptibility to Botrytis flower blight."

Here is a link that might be useful: calcium and Botrytis