Azalea chlorotic

I have an azalea in a large pot on the E. side of the house (So. Calif coastal), that has turned chlorotic. I gave it iron twice, but has had no effect; leaves still have that tell-tale appearance.
Light, water and fertilizer are normal.
Any suggestions?
TIA
Persephone
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Good question. I used tro think sulfur would adjust the pH.
Sincerely, John A. Keslick, Jr. Arborist http://home.ccil.org/~treeman and www.treedictionary.com Beware of so-called tree experts who do not understand tree biology. Storms, fires, floods, earthquakes, and volcanic eruptions keep reminding us that we are not the boss.
<Persephone> wrote in message

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Persephone wrote:

Chlorisis (yellowing of the leaves between green veins) is a symptom of poor nutrition, but does not reveal the source. It is usually caused by an iron deficiency. Many conditions can be responsible for an iron deficiency. Poor drainage, planting too deeply, heavy soil with poor aeration, insect or fungus damage in the root zone and lack of moisture all induce chlorosis.
After these conditions are eliminated as possible causes, soil testing is in order. Chlorosis can be caused by malnutrition caused by alkalinity of the soil, potassium deficiency, calcium deficiency, iron deficiency or magnesium deficiency. Iron is most readily available in acidic soils between pH 4.5-6.0. When the soil pH is above 6.5, iron may be present in adequate amounts, but is in an unusable form, due to an excessive amount of calcium carbonate. This can occur when plants are placed too close to cement foundations or walkways.
Soil amendments that acidify the soil, such as iron sulfate or sulfur, are the best long term solution. DO NOT USE ALUMINUM SULFATE; IT KILLS RHODODENDRONS AND AZALEAS. Foliar sprays of iron sulfate or chelated iron can reduce symptoms. A combination of acidification with sulfur and iron supplements such as chelated iron or iron sulfate will usually treat this problem. Chlorosis caused by magnesium deficiency is initially the same as iron, but progresses to form reddish purple blotches and marginal leaf necrosis (browning of leaf edges). Epsom salts are a good source of supplemental magnesium. Chlorosis can also be caused by nitrogen toxicity (usually caused by nitrate fertilizers) or other conditions that damage the roots such as root rot, severe cutting of the roots, root weevils or root death caused by extreme amounts of fertilizer. There is a tonic that remedies some cases of chlorosis.
Diane Pertson, Otter Point, Vancouver Island, found the following "foolproof formula" for chlorotic leaves or a rhododendron that isn't looking healthy:
Purchase a bag of Epsom Salts crystals (magnesium sulfate) (available here in bulk at farm-and-feed outlets), about $4.00 for a 5 lb. bag - and a bottle of FULLY Chelated Iron & Zinc (this is a very concentrated liquid - the chelation means it is in a form that can be readily absorbed by the plant), about $7.00 for 1 quart; In a one gallon watering can, put in 2 Tbsp. of Epsom Salts crystals and 2 Tbsp. of Iron and Zinc liquid - fill with warm water and stir to dissolve; Sprinkle this over the rhododendron - by that I mean drench the leaves with the solution and pour the remainder around the drip line of the root ball.
In 1-2 weeks, the leaves should be nice and green. You could repeat the process at this time if the leaves aren't fully green.
This works even better if, a month before, you have sweetened the soil by sprinkling a little Dolomite Lime on the roots. Very acidic soil can prevent the roots from taking up nutrients. As many of my rhododendrons are planted in very acidic soil under a canopy of giant cedar trees, I find an application of Dolomite and a light topdressing of mushroom manure in late spring is all they need.
If soil is too acid, the symptoms can be the same. Very acidic soil can prevent the roots from taking up nutrients. In the western USA where many rhododendrons are planted in very acidic forest soil, an application of Dolomite and a light topdressing of mushroom manure in late spring is all they need. Sprinkle the lime on in late winter, very early spring. Don't overdo it - just a light sprinkle. If it is mid-spring, get the lime on right away so the rhododendron roots will be able to take up the soil nutrients in time for new growth. If you don't have rain, water it in well.
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On Sat, 14 Jul 2007 18:12:21 -0700, Persephone wrote:

Check for tiny mites/insect damage. If there is no sign here, give it a half dose of acid fertilizer (such as Miracle Grow or a fertilizer for azaleas). You should see results in 2-3 weeks.
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Miracle Grow is more of a problem than a cure. It is very high in nitrogen which is not what azaleas need. It is water soluble so it is only a temporary measure designed to sell miracle grow. Hollytone is a good organic slow release, long-lasting, fertilizer but I only recommend using it once in the spring and at half the rate on the package.
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On Sat, 14 Jul 2007 18:12:21 -0700, Persephone wrote:

FWIW, here's the reply I received from my local nursery:
Ironite is the right way to go, but if the roots do not get enough oxygen to enable the plant to take in the trace elements (Iron,Zinc, Manganese etc) it will not help. What I mean with enough Oxygen, is that Azaleas could easily be planted too deep - they like to have the root ball be exposed, so I would recommend scraping the top layer away from the trunk and not keeping the soil soaked. A liquid fertilizer sprayed on the leaves such as soil acidifier should rectify the problem faster than if the nutrients were to be absorbed by the roots and transferred to the leaves. Persephone
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Persephone wrote:

There is some truth to what they are saying, but:
1) if the soil is not acidic, iron won't help. The soil must be acidic. The soil must be made acidic. Powdered sulfur will do this.
2) if the soil is deficient in potassium, calcium, or magnesium it will show the same symptoms but the iron won't help. Potash of Sulfur (K2SO4), Gypsum (CaSO4), and Epsom salts (MgSO4) will address these respectively if used in moderation.
3) if you have poor drainage the scraping the top layer of soil will cause puddling and make the problem worse. Using a raised bed with good acidic soil will address this problem.
4) if it isn't getting enough oxygen, it can be poor drainage and/or being planted too deeply. Using a raised bed and not planting any deeper than it was originally when purchased will solve both problems.
Unfortunately, most stores feed the customers desire to buy a product to pour on the problem and solve it. That doesn't always work.
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wrote:

The soil in this area is adobe (basic), but the people before me mulched regularly, as have I, so I suspectthat over many decades of modification the PH has become either acidic, or at least neutral. I should have it tested some time just out of curiousity, though I don't usually have problems like this.

Good drainage in that large pot. Water doesn't puddle.

I've scraped away some soil from the trunk; have refrained from over-watering, and will pick up some powdered sulfur.

That's probably true, but the email from the nursery was not pushy. I already have some Miracle-Gro; it probably won't kill the plant to get a moderate application.
Stay tuned!
Persephone
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Persephone wrote:

Neutral won't work. It must be acidic. A pH of 5 to 6.5 is necessary.

Miracle-Gro does more harm than good. It is a soluble nitrogen fertilizer. Your plant is stressed and feeding it nitrogen is not a wise move. The iron and sulfur are the right approach. Usually in alkaline soil such as yours the only easy way to grow azaleas is in a raised bed. Then the alkalinity of the surrounding soil doesn't affect the azaleas. The raised bed only needs to be 8" to 12" high. Then use a good acidic garden soil. If you want to raise acid loving plants like azaleas, you will have to meet them half way by providing acidic soil.
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wrote:

What about a large pot where soil can be modified?
Then the alkalinity of the surrounding soil doesn't affect

OK, suggestions assimilated.
I have had azaleas in that large pot on the E. side of the house before; they bloomed magnificently, but it's true they only produced for about 3-4 seasons.
I'll get some sulfur and see if it will work with the previously applied iron.
Persephone
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On Fri, 20 Jul 2007 15:20:35 -0700, Persephone wrote:

Where do you live, Persephone, I forget. If it is in a place with very hot summers it will be extremely difficult keeping azalea's healthy unless you have naturally occurring acidic soil.
In Dallas there is a strip of very acidic soil running through the center of town in the city. They have huge azalea's there which are healthy, vibrant and huge. They thrive through the heat because the soil is naturally acidic.
Just some added info to what Stephen already told you.
V
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wrote:

I live in Santa Monica CA, near the beach. It's always 10-20 degrees cooler than inland. We don't have hot summers. Ours is a near-ideal Mediterranean climate -- never too hot, never too cold. ('cept we're in our 2nd year of drought; had only 1 decent rain all last winter, plus a few chicken-shit showers). So -- lots of irrigating, or switch to xeriscapic which I'm considering.

was the right kind, but Stephen, I hope you're seeing this? Product is called "Sulfur Dust", by Lilly Miller. 90% sulfur, 10% inert ingredients.
What's confusing to me is that it's sold as a fungicide/insecticide. "For use on roses, grapes, citrus fruits, berries,nuts, vegetables, flowers, shrubs, trees. Controls powdery mildew, rust, scab, mites."
Doesn't say anything about acidifying the soil. Only mention of flowers is dusting or spraying foliage.
They said I could return it if it wasn't the right thing.
So -- can I in fact mix this with the soil of the azalea?
Or spray its foliage?
If this is the wrong product, could you describe the right one?
I know many on this NG are hostile to Miracle-Gro-type products, but they do make an acid fertilizer which I've never used. Is this something to consider?
TIA to all
Persephne.
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Persephone wrote:

Yes, this sulfur is just fine. It may be a WP (Wetable Powder), but in any case it is powdered sulfur.

You have to sprinkle it on top of the soil. If you mix it in to the soil you destroy the shallow roots of the azalea.
It is best to push back the mulch and then sprinkle it on the soil, then put the mulch back. Obviously you need to have the soil tested and determine the pH of the soil before you use it. The dosage is:
Present pH = 8 use 5.5 pounds per 100 sq. feet Present pH = 7.5 use 4.5 pounds per 100 sq. feet Present pH = 7 use 3.5 pounds per 100 sq. feet Present pH = 6.5 use 2.5 pounds per 100 sq. feet Present pH = 6 use 1.0 pound per 100 sq. feet
To convert to 1 square foot, divide by 100. So for every pound on the chart use 4.5 grams per square foot.
A teaspoon of 90% sulfur contains about 3.5 grams of sulfur. A tablespoon of 90% sulfur contains about 11 grams of sulfur. So:
Present pH = 8 use 2 tablespoons of 90% sulfur per sq. feet Present pH = 7.5 use 1 tablespoon & 2 teaspoons of 90% sulfur per sq. feet Present pH = 7 use 1 tablespoon & 1 teaspoon of 90% sulfur per sq. feet Present pH = 6.5 use 1 tablespoons of 90% sulfur per sq. feet Present pH = 6 use 1 teaspoon of 90% sulfur per sq. feet

There are chelated iron foliage sprays that can be used temporarily until the soil pH gets corrected. It takes time for powdered sulfur to adjust the pH. The sulfur is treating the soil, not the azalea. The reason you are treating the soil is because an alkaline soil will not give the azalea the proper nutrients.
The chelated iron foliage spray is a temporary way to get the correct nutrients to the azalea until the soil gets where it should be.

Miracid/Miracle-Gro Water Soluble Azalea Camellia Rhododendron Plant Food is a water soluble, nitrogen-rich powder and that is a very poor choice for outdoor azaleas. It is OK for azalea house plants and green house azaleas.
Miracle Grow does have a dry slow release azalea food: Miracle-Gro Shake 'n Feed Continuous Release Azalea, Camellia, Rhododendron Plant Food is a better choice for outdoor azaleas, but it is plastic coated chemicals.
The best choice is HollyTone. It is mostly organic natural materials that cater to the modest requirements of azaleas.
Now is not a good time to fertilize except with a chelated iron foliage spray.
Some chelated iron foliage sprays are:
Bonide Liquid Iron Lilly Miller IronSafe
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A wise man or woman once said: 'If you can't say anything nice, don't say anything.'
Googling "elemental sulfur, soil pH" brings up 645,000 hits which are mostly useless as are insults.
Googling ' "acidifying soil" azalea ' brings up 124 applicable hits but doesn't answer the other questions.
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Persephone wrote:

Usually they do best with a double pot with drainage holes in both pots. The outer pot is to protect the inner pot from the sun. Direct sun on the pot of an azalea can be bad, especially if the pot is not white. Even potted azaleas do better when the pot is sunk in the soil to help maintain even root temperatures and more even moisture. In the winter in colder climates the pots must be protected from freezing.
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