I have recently taken to growing some seeds from fruit from the local grocery store. I got some lemon seeds which out of the 4 i planted managed to obtain 3 seedlings which are each in their own pots with an orchid/sand/cactus mix soil with some added osmocote slow release granules as suggested many times on this forum, one thing that i have not found in this section which seems like an important question is how soon after the seedling is sprouted and growing nicely should you begin using water soluable fertilizer in addition to normal watering?
-smiley

Once the seedling has it's first true leaves.

Because you have added Osmocote slow release fertilizer to the growth medium, the tree will not require any additional fertilization, until the nutrient release time period listed on the fertilizer container's label has passed.

thank you for your guidance, i'm sure my plants appreciate it as much as a plant can.