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Calcium for rust-prevention in roses

Posted by Strawberryhill 5a IL (My Page) on
Sat, Aug 24, 13 at 15:18

I first read about calcium's role in preventing rust in Texas rosarian Field Roebuck's "Complete book on roses". I also found a government abstract on the role of calcium in rust prevention.

Here's an excerpt from the link below "Results indicated that plants growing in more stressful low-calcium soils experienced higher rates of rust infection, suggesting that soil calcium may modulate host susceptibility in a manner opposite to that predicted by the a priori hypothesis."

Here is a link that might be useful: Effect of soil calcium on fungal infection


Follow-Up Postings:

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RE: Calcium for rust-prevention in roses

Or is it stress of whatever kind that makes a plant a "sitting duck" for problems?

I would think TX soils would have plenty of calcium.


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RE: Calcium for rust-prevention in roses

Hi Jean: I'm next to limestone (calcium carbonate) quarry, and within walking distance from a gypsum manufacturing plant, yet my soil is tested barely adequate in calcium.

EarthCo. that tested my soil recommended applying gypsum for my alkaline clay, pH 7.7. Calcium is plenty in my soil, except it's tied up with phosphorus and magnesium. Gypsum, calcium sulfate, is in a form that's readily available to plants.

My neighbor had blossom-end rot on his tomatoes and told me he's applying gypsum. My soil test came back recommending the same. I tested soluble gypsum on my roses. AMAZING RESULT, immediate green-up of my pale roses both in pots and in the ground.

In my 30 years of growing roses I had never seen such fast-green-up. I now have 55+ roses. My garden is listed in HMF. If you google "Chicago IL 5a and HMF" you'll see pictures of my no-spray garden.

When I research on Soluble gypsum, there are several studies that showed better-uptake of ammonium (for nitrogen) & trace elements, and preventing nutrients-tied up with bicarbonates (calcium hydroxide) in alkaline tap water.

My B.S. is in Computer Science, minor in chemistry, so I researched everything thoroughly, before wasting money buying gypsum. It's cheap anyway, $6.99 for a 40 lb. bag at my local feed store.

Below is Samaritan floribunda (Harkness English rose) bought from Roses Unlimited end of June. It was very pale (yellowish) when planted in my alkaline clay (pH 7.7), until I gave it soluble gypsum ... with immediate green-up. The rootball is planted 6" below soil level for my zone 5a winter, that's why it looks so short.

This post was edited by Strawberryhill on Sat, Aug 31, 13 at 14:13


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RE: Calcium for rust-prevention in roses

My Evelyn rose came down with rust, thanks to the new acidic and wet horse manure. The stable stops liming this year, and switched to wet straw and strips of wood shavings for bedding.

I applied soluble gypsum to Evelyn, sold for $10 for 5 lbs. at Kelp4Less, free shipping. The rust cleared up on Evelyn. That soluble gypsum worked immediately, versus the granular one bought from Menards ($6 for a tiny 1 lb. bag), which gunked up on top.

Later I found my local feed store sells gypsum $6.99 for 40 lbs., smaller pellets that dissolve easily in water. If calcium sulfate (gypsum) is applied, potassium should also be applied. There's an inverse relationship between calcium and potassium: too much potassium drives down calcium, and vice versa.

Potassium helps with prevention of rust and black spots. Potassium sulfate (sulfate of potash) has lower salt index at 43, than muriate of potash (potassium chloride) with a salt index of 116.2.

When I researched on pH level and nutrients deficiency, several University Extensions cited less potassium and calcium available when the pH is lowered.

Here is a link that might be useful: Soluble gypsum for $10 per 5 lbs. at Kelp4Less

This post was edited by Strawberryhill on Sat, Sep 21, 13 at 21:37


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RE: Calcium for rust-prevention in roses

There's an interesting recipe for blackspot prevention in Yahoo! Voices, where A.C. O'Brien blended banana peels (high in potassium), with calcium, baking soda and spray roses ... very effective for black spots! See link below:

Here's an excerpt of the below link: "I filled my blender with a banana for the potassium portion of the mix, I added a heaping table spoon of soda bicarb (aka; baking soda) I put in a few calcium rich antacid tablets for calcium ... I know that plants like calcium ... I added two large cloves of very crushed garlic to the mixture, knowing that garlic inhibits the growth of almost all viruses and fungal diseases inspired this addition. I than added enough water to cover the banana and antacids in the blender and gave in a good spin. .... I added about an ounce of the "smoothie" mixture to a pint of water shaking it well, I let it 'brew for about an hour, then strained it to get it through the spray bottle nozzle."

Here is a link that might be useful: Cure black spots with potassium in banana peels


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RE: Calcium for rust-prevention in roses

I explained to a friend the difference between hydrated lime in tap water, versus natural lime in soil. Here's the info I wrote to her:

My neighbor uses Ball Professional Potting soil, the #1 recommended soil for seedlings. It's 45% composted pine fines, peatmoss, perlite, vermiculite, lime, and gypsum. The last 2 ingredients: lime is a fungicide, and gypsum has both calcium and sulfur as plant nutrients.

Composted pine fines also have tannin, a fungicide. I tested the pH of that potting soil, and it's neutral (clear) in red cabbage juice, versus pinkish (pH 6.5) of MiracleGro potting soil (green bag). MG potting soil is high in peatmoss. The result? Wet on top and hosted whiteflies when I grew herbs in the basement.

I checked on whiteflies and many folks report topping with composted worm casing keep the whiteflies off. I checked the pH of compost worm castings, it's neutral to alkaline.

The problem with peat-based potting soil is it holds water, making the surface wet to nourish pests (whiteflies) and pathogenic fungi. Composted fine pines dry out faster than peatmoss, and provides better drainage. All living things require water to thrive, and if the surface of soil is dry, less microbes.

More of U. of CA extension: "Aluminum foil or reflective plastic mulches can repel whiteflies, especially away from small plants."

There's logic in waiting until the soil is completely dry, before watering. Keeping surface dry and alkaline is the key to healthy plants. Peat moss-based soil retains surface moisture longer.

I get HUGE black spots the size of a quarter, on Comte de Chambord when I had him in acidic, poor drainage, wet peat moss potting soil, plus topped with sticky, acidic alfalfa meal. But when I planted Comte in my alkaline soil, no diseases whatsoever. My soil is high in lime, pH 7.7 ... Lime is a fungicide. Lime pellets is expensive, but crushed limestone is cheap at $2.49 for a big bag, plus it doesn't raise the pH fast like lime pellets.

My soil is speckled with crushed limestone and dolomitic lime (these are natural forms, and don't hurt plants). The hydrated lime in tap water is different, it's a bicarbonate made by reacting calcium at high temp, not natural, and bad for plants. Hydrated lime, or calcium hydroxide is unstable, quickly raise pH, and binds with phosphorus, potassium, and iron ... thus less available to plants.

My roses in partial shade, watered once or twice a year, are much healthier than roses in full-sun, watered frequently during the drought.

From Wikipedia: "One significant application of calcium hydroxide is as a flocculant, in water and sewage treatment. ... It is also used in fresh water treatment for raising the pH of the water so pipes will not corrode."

Here is a link that might be useful: Wikipedia on Calcium Hydroxide

This post was edited by Strawberryhill on Thu, Oct 31, 13 at 11:32


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RE: Calcium for rust-prevention in roses

I'm still looking up info, but I wonder just how AVAILABLE calcium is in Texas soils. Yeah, lots of the state is covered with limestone & caliche but I wonder whether plants can use the calcium in calcium carbonate (caliche). I've seen noticeable improvement in color & vigor of roses that I gave a dressing of gypsum (calcium sulfate) to. I don't know whether they're adsorbing iron better because of the sulfur, or getting a more available form of calcium, or what, but the improvement is there.

As an analogy, back in an animal nutrition class I took, the professor told us that iron oxide is unavailable to cows, but that it's added to salt licks to color them red because people associate "iron" with "red". I forget what form of iron IS useable (sulfate?) but the point was that to market salt licks, the unusable oxide was added also to make them LOOK like what people instinctively associate as "iron". You can get yellow or white licks but most folks buy the red ones.

So I'm wondering whether it's a mistake to look at the white, chalky caliche that's all over the surface around here & assume that plants have all the calcium they need--maybe calcium carbonate isn't a useable form, or maybe the alkalinity reduces adsorption, or whatever.


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RE: Calcium for rust-prevention in roses

Hi Bluegirl: You are right about "the professor told us that iron oxide is unavailable to cows." I already tested iron sulfate on my rhododendrons ... didn't green up, but leaves turned brown, and the plants died.

Iron sulfate burns root fast, it's very acidic, but plants can't use that. Chelated iron is in a form that plants can use. That's why I use Wholesome Organics molasses with 20% chelated iron, 20% potassium, and 17% calcium ... that greened up Excellenz von Schubert rose immediately. That rose is known for chlorosis and prefers acidic soil.

People make the wrong assumption that lime added to tap water provides calcium to plants. They don't realize that form of lime, calcium oxide, is unstable, and binds with iron, phosphorus, and potassium ... making plants yellowish. See below from Wikipedia:

"Calcium oxide is made by the thermal decomposition of materials such as limestone. This is accomplished by heating the material to above 825 °C (1,517 °F),[5] a process called calcination or lime-burning, to liberate a molecule of carbon dioxide (CO2); leaving quicklime. The quicklime is not stable and, when cooled ... after enough time, it will be completely converted back to calcium carbonate .... Calcium oxide is a key ingredient for the process of making cement."

Calcium hydroxide is calcium oxide mixed with water. It's used in fresh water treatment for raising the pH of the water so pipes won't corrode. My tap water in my last house was neutral ... roses bloomed OK when watered with tap. But my tap water in my current house, alkaline soil, is hard-well water, pH 8. The soil where I watered with tap turned concrete, compare to the soil where it's just rain water. The practice of adding calcium hydroxide to water to prevent pipes from being rusty, is what glue up clay soil further, and raise the pH.

Thus I get less flowering when watered with my tap (pH 8), versus rain water (pH 5.6). I put rock-hard limestone clay under drain-spout where rain water pours ... they become fluffy fine particles. Rain water (pH 5.6) through time can convert limestone into gypsum ... I already double- checked with the chemist in the Soil Forum. Gypsum occurs naturally and also is made by reacting sulfuric acid with calcium carbonate.

Too much gypsum can hurt. Here's an excerpt from link below: "From intensive field observations of gypsiferous soils in Iraq, Smith and Robertson (1962) found that root growth was inhibited where the gypsum content of soil was over 10 percent."

"Van Alphen and de los Rios Romero (1971) conclude that up to 2 percent gypsum in the soil favours plant growth, between 2 and 25 percent has little or no adverse effect if in powdery form, but more than 25 percent can cause substantial reduction in yields. They suggest that reductions are due in part to imbalanced ion ratios, particularly K:Ca and Mg:Ca ratios" K stand for potassium, Ca stand for calcium, and Mg stand for magnesium.

That's why I use gypsum (17% sulfur and 22% calcium) to break up hard clay at the bottom of the planting hole .... and use sulfate of potash (23% sulfur and 20% potassium) to neutralize my pH 8 tap water. My pH 7.7 clay soil is tested exceedingly high in magnesium, Mg is what makes clay sticky.

Calcium and potassium together help with best bloom formation. Below is a bouquet of roses: Radio Times (pink), Crown Princess Magareta (orange), and Paul Neyron (dark pink). They are fertilized with gypsum and sulfate of potash.

Here is a link that might be useful: Effects of gypsum and calcium carbonate on plants

This post was edited by Strawberryhill on Thu, Oct 31, 13 at 11:55


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RE: Calcium for rust-prevention in roses

surfing around, it seems many sources on desert soils value gypsum. One site I was reading states that the calcium in calcium carbonate (caliche) IS NOT available to plants, it's too tightly bound for uptake.

If that's right, gypsum would be a good ammendment to supply calcium & fight alkalinity by releasing sulfur, which would help make elements like iron available.

It's counter intuitive to look at the bleached white desert surface around here & realize that all that calcium isn't in an adsorbable form for plants to use.


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RE: Calcium for rust-prevention in roses

Gypsum (calcium sulfate) is a better approach to provide calcium to plants. Someone wrote to me about losing 3 of her rose bushes when she put bone meal on top .. tons of maggots. Another person reported about maggots and flies in tomato plants after adding bone meal, see link below:

I didn't have that problem, but I burnt a dozen of geranium plants by putting bone meal on top. High phosphorus can really burn, best used as soluble diluted in water.

Here is a link that might be useful: Maggots in plants after adding bone meal


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