Rhododendrons / Azaleas

Deficiency symptoms and their signs:

When problems arise with rhododendrons and azaleas, chances are, the main problem you may have with your plant is associated with the planting site, soil, drainage, wind, etc. Through a process of elimination, first consider the site placement, second inspect for insects & diseases and third you may want to consider these nutrient deficiencies. If deficiencies are the problem, they can often be corrected by applying the proper chemical nutrients, however, nutrient deficiencies will usually occur when a plant is sited improperly. This means that the soil is naturally lacking these nutrients, so the site placement is unsuitable. If a plant is old and well established and the soil for some reason has become exhausted, then the addition of these beneficial nutrients will help.

Symptoms: Lighter colored foliage than normal, stunted or very little growth, thin stalks or under severe conditions the lower or older leaves become pale yellow.

Deficiency: Nitrogen.

Symptom: Foliage becomes darker than normal and plants become stunted. The stalks and the lower leaves become purplish. The older leaves will show symptoms first and most severely. Plants that are mildly deficient will have a dull appearance on the older leaves.

Deficiency: Phosphorus

Symptom: Foliage is always affected on the older, lower leaves first. Leaf margins begin to die, they turn brown and curl under, the leaves eventually turn brown and then drop off.

Deficiency: Potassium

Symptom: Older foliage turns light colored to nearly yellow ,while the veins will remain green. A slight yellowing of the older leaves outer foliage may be the only visual symptoms and the leaves will tend to drop before any further chlorosis occurs.

Deficiency: Magnesium
These four elements mentioned - nitrogen, phosphorus, potassium and magnesium are mobile in the plant and therefore symptoms will always appear first on the older foliage. Other elements such as boron, calcium, copper, iron, manganese, molybdenum, sulfur and zinc are not mobile in the plant and therefore deficiency symptoms will generally appear on newer growth.

Symptom: New growth foliage first appears pale green between the veining, progressing to yellow-green or yellow. If the deficiency becomes acute the leaf margins and tips will turn brown and die.

Deficiency: Iron

Other concerns with rhododendrons:  

Symptom: Older foliage turns yellow and or brown and fall off the plant.

Cause:

Rhododendrons, like all evergreens eventually shed (or lose) their inner foliage several years or more after they emerge, this is normal leaf senescence. Some varieties will lose their leaves before the onset of winter and some during periods of drought in the summer. No need to worry this is normal.

Symptom:    A variety of leaf discolorations, most being brown dead areas with no particular shape or pattern.

Cause:

Although most people would not admit to it and often they attempt to treat it as a fungus disease, this type of symptom is caused by the misuse of a chemical such as herbicides, insecticides or even liquid fertilizers. More is not always better, in fact the stronger the fertilizer solution, the greater chances of burning the plants foliage or roots. Follow instructions on all products carefully.

Continued Helpful Azalea and rhododendron tips