What is wrong with my mahonia and philadelphus?
Jennifer Sadler, by email
Stefan says: Your philadelphus is in a pot and your mahonia is in the garden, but both are displaying some form of discolouration to the leaves. I believe they do have something in common, however, because neither is suffering from pest or disease but from something placing the plants under stress.
Stress is a catch-all expression for a condition that is generally the result of a shortage of either water or nutrients. I have to say that philadelphus is a pretty vigorous shrub to have in a container and stress is always likely to arise in such a confined environment. And although mahonias are well adapted to growing in dry and relatively impoverished conditions, I think both your plants need constant attention to feeding and watering.