Why do rhododendron leaves turn yellow?

Answer

Rhododendron leaves turn yellow because of sun exposure, according to the Victoria Rhododendron Society. Sunlight tends to bleach exposed leaves. When this occurs, adding nitrogen helps turn the leaves green again.

The Victoria Rhododendron Society adds that older leaves naturally turn yellow, and they are replaced every one to three years. When the leaves are yellow but the region along the veins remains dark green, the plant likely suffers from chlorosis, which is caused by a magnesium, nitrogen or iron deficiency. In this case, the soil’s pH must be checked. A very high pH hinders the plant's ability to absorb necessary trace metals. If the pH is close to 5.5, adding Epsom salts is a recommended solution. If this does not work, it helps to add a nitrogen source and chelated iron.

Chlorotic leaves are usually a sign of iron deficiency and can be dealt with by using iron sequestrene, according to the Millais Nurseries. Chlorosis is also caused by poor conditions, such as drought, soil pH or drainage problems. Over-fertilizing must be avoided, as the edge of the leaf will likely turn dry and brown. Chicken and farmyard manures are not advisable as fertilizers, because they contain too much nitrogen for rhododendrons. Similarly, bonemeal must be avoided, as it has too much calcium.

Q&A Related to "Why do rhododendron leaves turn yellow?"
I think it's a deficiency of nitrates, which help plants to produce chlorophyll, and which is the pigment that turns leaves green, and without it, leaves can become yellow.
http://wiki.answers.com/Q/What_causes_yellowing_le...
Not all rhododendrons are the same. Certain cultivars, or strains, have inherently spotted leaves even when perfectly healthy. These spots are a faint purple, not rusty red or dull
http://www.ehow.com/about_6746763_rhododendron-lea...
This is called Chlorosis and it means the green chlorophyll is not present. All you are seeing is the other leaf pigments that are normally not noticable because they are masked
http://www.quora.com/Gardening/Why-do-the-leaves-o...
The chlorophyll mostly made with magnesium is gone, due to lack of sunlight making no food nor energy for the plant to create more. In the room though its just a lack of water to
http://wiki.answers.com/Q/You+leave+a+green+leaf+i...
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