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Azalea chlorotic
Persephone wrote:
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. 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. -- Pardon my spam deterrent; send email to Visit my Rhododendron and Azalea web pages at: http://rhodyman.net/rahome.html Also visit the Rhododendron and Azalea Bookstore at: http://rhodyman.net/rabooks.html Cheers, Steve Henning in Reading, PA USA Zone 6 |
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