You did not mention what
Osmocote product you had previously used so we cannot verify for sure but it is always recommended to follow the instructions on each individual product label to ensure that the product is applied properly. When done so, products should not harm a plant. We would advise that you contact the manufacturer of the
Lilly Miller UltraGreen for the best advise for your issue. They can be reached at 1-800-265-0761.