Rhododendron pH

m_taggart(7b)November 25, 2007

Returned to my parents house for x-giving and noticed pale spotting on their rhodies. I tested the pH and found it to be around 6.8. I added enough garden sulfur to lower it to around 5 to 5.5. Does anyone have any pictures of a rhododendron suffering from too high a pH. I'm thinking this led to an iron deficiency. Anyone have this trouble before?

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rhodyman(SE PA, USDA Z6)

If the pH is too high or there is iron deficiency, the leaves turn yellow with green veins. It is called chlorosis.

Chlorosis 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, magnesium deficiency or too much phosphorus in the soil. 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. For a quick but only temporary improvement in the appearance of the foliage, ferrous sulfate can be dissolved in water (1 ounce in 2 gallons of water) and sprinkled on the foliage. Some garden centers sell chelated iron, which provides the same results. Follow the label recommendations for mixing and applying chelated iron. 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.

Here is a link that might be useful: How to grow rhododendrons and azaleas.

    Bookmark   November 26, 2007 at 11:00AM
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