Question
Red Tip Photinia
Hi James. I live in the high desert - Cottonwood area, 3500 ft elevation, of Arizona. I have several red tip photinia shrubs planted 13 years ago and that have reached 9-10 ft in height. Our soil is heavy caliche, so I had a strip dug out and had sandy river-bank-source soil brought in. Most years, a considerable number of the leaves become medium yellow. Local master gardeners tell me that it depends on which growth are yellowing. New growth showing yellow indicates Nitrogen deficiency -- mature growth turning yellow indicate Iron deficiency. Since the yellowing leaves are both at the top as well as the bottom of the plants, I can not tell the new growth from mature. I applied both high Nitrogen food, and later, I applied chelated iron followed by commercial Ironrite. Both applications were into a circular ditch located at the outer edges of the plants, and watered in well. I now view a considerable growth of new, red-brown-gold colored leaves, located everywhere, on the plants. However, I still have lots of the yellow-green leaves.
What is your opinion -- is it a deficiency of Nitrogen or deficiency of Iron? Thank you. Richard
AnswerHi Richard, Check your pH. It should be between 5.5 - 6. If the pH is out of line, many nutrients that are present are locked up in forms unavailable to the plant. Ironite is a great product, but very acidic.
If the pH is correct, then let's rule out water. It is possible that the soil you replaced is now full of roots. It is possible the yellow foliage could be from too much or too little water if the sandy soil is totally full of roots. Water can make iron unavailable.
There was a case a number of years ago with maple trees planted in a city's median. About 30 years after planting, they all started to appear diseased and then die. The original soil was removed and it took 30 years, but the roots never got out of the loosened soil and eventually died from root constriction and nutrient problems.
You might dig a hole about 12" deep between two of the plants. See how many roots are there and then fill it with water and see how quickly it is absorbed. Gone in 5 minutes and they need more water. Still there in 4 hours, they could be drowning.
When you dig the hole, look for tunnels and soil insects so we can rule out root damage from them.
I really think your pH is off. Let me know what you find. Jim
