I am not sure how close to the crape myrtle your mums are, so it's hard to say. If your original mums grew well I wouldnt spend a lot of time and money on amendments. Both crepes and mums do ok in poor soil. You can plant your mums and just top dress with a couple of inches of compost.

I don't know why you are working the soil unless it's depleted or hard panned. If you dig to deep and are to close to the crepe you can damage roots, so be very careful.

its hard to be specific without knowing more about the situation. Mums are pretty hardy, just sunlight,water and a little compost or manure for food. They seem to take care of themselves for me.

hope this helps

Thanks. I should have been more specific. The mums propagate themselves, so they have many stems. The stems are almost bare, but there are leaves on the tops of the plants.

I think I should put in some compost since I am replacing the plants with new plants. When I replace a rose, I always mix new soil and compost with what is there since I think I am supposed to, and roses would all use up the same nutrients.

I thought I had watered them enough, but I have been remiss, and have not piled on mulch. That is bad in this heat.

Thanks for the response.

Sammy