I have some calibrachoa planted in window boxes with good quality compost along with a bit of vermiculite, swell gel and slow release feeding. I have them planted up for about a month or more but have noticed where the leaves of some of them are turning yellow and wonder what could this be. They were planted up in the greenhouse and were taken outside about a week or so ago. Some of them don’t seem to have been affected and have kept their good green leaf colour.
They may have got a set back going out but should grow out of it, Some plants may have been a bit stronger and not suffered, or conditions were right. Check watering is okay.