A reader posted a comment that sent me to the Internet for research.
The comment was that "petunias and calibrachoa (million bells) can benefit greatly with a little PH manipulation. They prefer a slightly lower PH and regular fertilization. A little garden sulpher (available at Lowes) works great."
Million bells actually is a petunia.
The reader will be happy to know that their experience regarding those flowers' pH preference was studied at Rutgers and Cornell Universities. Thanks for the tip and the reminder that it is important to provide the correct pH levels for good gardening results.
Here's a link to the study and an excerpt is below.
Northeast Greenhouse IPM Notes
May 2006 A publication of Rutgers and Cornell Cooperative Extension Vol. 16, No 4
Puny Calibrachoas? It May be Thielaviopsis
We attributed this disease reduction to a pH effect: lower pH will help the plant and suppress the fungus. Aim to keep pH well below 6.0 for best results; pH 4.8 will prevent disease development in field soil. Many calibrachoas are prone to iron deficiency at high pH, so lowering their growing pH can help reduce iron chlorosis as well as disease symptoms.
Tips for Yellow Tips Karen Kackley, J.R. Peters Laboratory
Many growers are seeing yellow growing tips on members of the “petunia group” (e.g. petunia, calibrachoa, bacopa, scaevola, nemesia, diascia, and pansy). The most usual cause of yellow tips on these plants is iron deficiency due to high pH in the growing medium. Members of the “petunia group” grow best when the pH in the medium is between 5.4-5.8. At higher pH levels, iron and other micronutrients become insoluble and unavailable to plants.
When yellow tips are detected, the first step should be to determine the pH of the growing
medium. Do this by sending a sample to a horticultural testing laboratory or by doing in-house
testing. It is important to remember that while iron deficiency due to high media pH is
the most common cause of yellow tips, it is not the only cause. High phosphorous, low iron
and imbalances with manganese, zinc and copper can also result in iron deficiency. If
high pH is detected, efforts should be directed at correcting this situation. One of the most
common causes of high pH in the growing medium is the use of high alkalinity water. A
complete laboratory water analysis will determine the level of alkalinity in water and
supply the information needed to determine the amount of acid required to correct the problem.
In the meantime, growers may wish to use corrective iron drenches.