Certified GKH Gardening Expert
That is either a sign that your soil is infected with a fungus, or very severe nutrient burn.
Be sure that you test your soil before feeding, to ensure that there is, indeed, a need to feed them.
Make sure that the container does not allow any water to stand inside it. Make sure that there are plenty of drainage holes drilled to allow any extra water out.
You may need a fungicide or bactericide to combat fungal issues. Outside of that, proper planting practice will be the way forward.
Here are some articles that will help:
Wow, thank you very much for taking the time to help. I appreciate it very much!