I was just thinking, when you top dress the OSF, I would only use half the recommended dose or less per gallon of soil. That's what I did evenly with my outdoor plants. It gives you directions for when your mixing soil, not top dressing. I'm not sure if it would harm your plants or not at full strength.
The way OSF works is some is available to the plant immediately and some breaks down over time. So you should only need one application pet grow at full strength. 1 to 2 tbsp per gallon of soil seems like a lot watered in at once. Especially in be pots. I always err on the side of caution when adding anything new to my plants.