What instructions are you following to get your application rate? Osmocote for tomatoes recommends 1.5 capfuls per 4 square feet mixed into the top 3 inches of soil/mix. Thats about 1 tablespoon per square foot. A 20 gallon pot might be around 2-3 square feet, so 2-3 tbsp per pot. If you try a much lower rate like this and find you have a nutrient deficiency, you can always supplement later, but you cant take it away once its there
Sent from my iPhone using Tapatalk