Bert’s post yesterday reminded me of some work one of my graduate students did about 10 years ago. We were curious to see whether a transplant fertilizer containing phosphate was correlated with foliar iron deficiency, which is visualized as interveinal chlorosis:
What Scott did was to plant 10 rhododendrons per treatment into pots containing containing a name brand azalea, camellia and rhododendron food (5-5-3) at 0, 0.5, 1.0, and 2.0 times the recommended amount. Here are some of the results of that study:
Total number of chlorotic plants
Total foliar iron vs. fertilizer treatment
Chlorosis as a result of phosphate fertilizer. 1= Normal (green leaves), 2= Light chlorosis in young leaves, 3= Moderate chlorosis, 4= Severe chlorosis, young leaves white
For gardeners, the take home message might be that the control plants – those without any transplant fertilizer added – did the best. Don’t add phosphate to your landscape and garden soils unless you have a verified deficiency. And only a soil test will tell you this conclusively.
You can’t fly by the seat of your pants on this one, folks.