Question
You appear to be in my area of the country (southern Missouri) so I hope you have seen or heard of my problem. I am zone 7 due to being on the south side of Table Rock Lake. Very rocky, so I grow in containers (perennials and shrubs). My agastache cana, Sweet William, and zauschneria have all developed yellow leaves with green veins. It started last summer, and this spring the plants are totally yellow. I tried iron, nitrogen, fungicide, pesticide. They were fertilized with Osmocote last spring. I have lost one Sweet William and maybe one zauschneria so far.  Have you any suggestions?  The agastaches look healthy, but the others look a little "sick".

Answer
Hi Anne,
Thanx for your question.  Are you watering your plants too much?  Sometimes when you fertilize and/or water too much, the leaves of a plant will turn yellow.  Agastache actually prefer some drought.  If you're planting in containers, you have to be sure not to let it dry out too much.  Sounds like your Sweet William may have rotted.  Sounds like too much water to me. Stop fertilizing and water only when the top of the soil starts to drop out and see what happens.  I hope this helps.
Tom