Azalea sun requirements

redsox_gwAugust 14, 2007

What is the minimum sun requirement azaleas have in order to thrive? Also, what is the maximum amount of sun they can take? I planted 3 new azaleas this year at our new house and there is much more sun in the area than I anticipated. You know they say to wait a year before planting anything....this is why.

They are really in full, full sun and this summer has been an unbearable scorcher. Should I move them this Fall/next Spring or leave them be?

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morz8(Washington Coast Z8b)

How bad do they look this first year? Much leaf burn?

The amount of sun an azalea can take without damage depends on the ancestry of the hybrid, or native habitat of the species, where in the world you have your garden. Ideally, they perform best with as much sun as the foliage can stand without burning, sunlight promotes heavy flower production and compact growth while properly maturing the plant to resist winter cold damage.

The number of cloudy days during the growing season comes into play, as does your proximity to a large body of water. (i.e., lots of cloudy days here, next to the ocean and I can grow in full sun, both small leaf azaleas and large leaf rhododendrons)

Are they especially damaged after your scorcher summer, and if you know which azaleas you have, it might be easier to tell you their reputation for resistence to burn once established.

    Bookmark   August 14, 2007 at 10:04PM
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Not a log of leaf burn, just yellow leaves. Of the three, one lost a good number of lower leaves in the Spring. I would blame it on my alkaline soil, but the other 2 did fine. Do azaleas like acidic soil?

The only azalea that had a tag is "pink ruffles" azalea. The tag does say "part sun." I would imagine the other 2 are of similar variety. I guess I would take part sun to mean 4 hours or so?

    Bookmark   August 16, 2007 at 1:05PM
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morz8(Washington Coast Z8b)

Pink Ruffles is a Rutherford hybrid that would probably do best in afternoon shade in your warmer zone. Azaleas seem to be a popular landscape shrub in Kentucky from what I can see - do you know your approximate soil ph?

While sunscald can account for yellowing leaves, azaleas do need acidic soil to thrive...if yours is alkaline, you are going to need to do something to adjust the PH if you want to grow azaleas.

    Bookmark   August 16, 2007 at 8:06PM
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rhodyman(SE PA, USDA Z6)

It is easy to tell the difference between sun scald and chlorosis which is caused by poor soil conditions.

Sun scald yellows the part of the leaf most exposed to the sun. It is usually the central area of the leaf near the central vein.

Chlorosis yellows the entire leaf except for the veins which remain dark green.

Sun scald is common on plants which get too much sun or plants which were pruned and leaves that were in the shade of the other leaves are now getting full sun and scorching since they were not adapted to full sun.

Chlorosis is caused by a lack of nutrients. This is normally caused by soil that is not acidic enough. But, it can also be caused by potassium deficiency, calcium deficiency, iron deficiency, magnesium deficiency, nitrogen toxicity (usually caused by nitrate fertilizers) or 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. In any case, a combination of acidification with sulfur and iron supplements such as chelated iron or iron sulfate will usually treat this problem. Holly-tone contains these elements and 4-6-4 fertilizer. It is best applied in the spring prior to blooming to make sure the plant is healthy when forming next year's flower buds. If you missed applying it in the early spring, it can be applied up until mid summer. Do not apply now. Rhododendrons do best when left alone in the right conditions. You don't need to use Holly-tone or any fertilizer unless the plant shows signs of malnutrition.

    Bookmark   August 17, 2007 at 7:55AM
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I don't know why one bush might have had chlorosis and not the others. My soil pH is very high....up to 7.7 in some areas. We did treat with aluminum sulfate later in the Spring. I fertilized with MiracleGro around blooming time. Do azaleas only need to be fertilized once, in Spring?

Seeing as my soil is so alkaline, what would I treat with in Spring? The aluminum sulfate again or something else? I guess I will buy a pH meter of my own.

    Bookmark   August 17, 2007 at 10:15AM
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rhodyman(SE PA, USDA Z6)

Never use aluminum sulfate on rhododendrons or azaleas. Once may be OK but never again. Aluminum builds up in the soil and is toxic to rhododendrons and azaleas. Use sulfur powder or iron sulfate instead. In your case, you need to use a raised bed since otherwise you would constantly be fighting the alkaline soil. The raised bed needs to be about 8" to 12" high and filled with good acidic soil. Some people use landscape timbers around the raised bed. This will be easy to keep acidic. Trying to make soil that is 7.7 acidic is like *issing in the wind. Any time it rains, alkaline water will come into the area you are trying to make acidic. It is also important to check your irrigation water. If it is alkaline, don't use it; use rain water instead.

Regarding the aluminum sulfate you bought, it is for hydrangeas but not rhododendrons and azaleas. In fact hydrangeas need both aluminum and acidity to turn blue. It may have been labeled for azaleas, but not all companies are ethical about this. It is well documented that use of aluminum sulfate will eventually poison many plants including rhododendrons, azaleas and eventually even blue berries.

Here is a link that might be useful: Making Soil Acidic for Azaleas (Don't use Aluminum Sulfate)

    Bookmark   August 17, 2007 at 6:21PM
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I guess the aluminum sulphate is why my azaleas are sick-looking. I wish I'd read this sooner! Is there anything that can be done to the soil if there is an aluminum build-up? Is aluminum harmful to other plants/trees in the same area?

    Bookmark   May 9, 2009 at 2:50PM
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