I have planted annual vinca with hydrangeas, verbenum, marigolds, perennial hibiscus. Everything except the vinca is thriving. The vinca all have yellowing leaves with dark green veins. They are scattered about in a 4 x 4 foot bed with the others above.

It looks like a nutritional deficiency of some sort (nitrogen? iron?) But why wouldn't the other plants also be effected? I fertilized everything at the same time with osmocote. It all gets watered the same. Full sun.

Any thoughts?