Question
Hello James,  I have a number of 8' - 10 Red Tip Photinia  planted in silty soil. Last year most of them had the light green to yellow leaves with brown spots. I  was told that the problems were an alkaline soil and lack of iron.  I amended the soil with soil sulphur, then later added chelate powder and Ironrite.  In addition, I added some Superthrive (I know -- there is no scientific evidence that Superthrive contains anything to assist plant growth)and also Colorbrite plan food.  The shrubs did respond to some degree. This spring, most of the leaves are green, but small.   My water is from a well in the high desert of Arizona with high degree of hardness.  Should I have the soil analyzed for PH and then work to "stabilize" it, and what is your suggestion regarding the Iron deficiency?  Do you beleive in spraying chelated Iron solutions onto the plant foliage?  PS, all of the Photinia in the Cottonwood/Clarkdale, AZ,  area are now a beautiful golden-red.   Any suggestions

Answer
Hi Richard, Photinias should do well with a pH between 5 and 6. A soil test would be the first step and I'd want to test for soluble salts also.  Where I live, photinias are very difficult to grow.  They are in the rose family and get a nasty leaf spot disease which I would want to rule out.  Have a local nurseryman take a look at it.
Superthrive is not a fertilizer, it is a bio-activator and I have seen some plants survive after repeated applications that I thought should have died.  I like the product and have used it for years.  
How quickly does your soil drain?  Dig a hole about 12" wide and deep and fill it full of water.  Soil that is saturated locks up iron in forms unavailable to the plant, so good drainage is a must.  The hole should be empty in a couple of hours.  If it's empty in 15 minutes, we need to add organic matter to help hold moisture and nutrients.  If it's still full tomorrow, we need to elevate the bed so gravity pulls water down below your root zone.  
Can we rule out herbicide damage?
Were these healthy at one time and suddenly start looking bad? Has anything changed...drainage, new construction? Is there evidence of rodent burrows, sap oozing?  
Are other plants suffering?  They should be if it's soil related.   
One problem I see is what I call "post hole syndrome". If plants are not properly planted, roots often curl around each other never getting out of the original hole and they strangle themselves.  I would expect this to become evident is plants that are 5-10 years old.
There are many things that could be causing their problems.
Find a reputable independent nurseryman.  Chances are if you are having this problem, others are too, and he's probably seen it.  Jim