Sounds like a wonderful project you are doing. I'm not sure I understand your question. Are you spraying this on the ground or on the weeds? You shouldn't be spraying it on the ground, but on live green leaves of weeds. Do be VERY careful as vinegar is non-selective and will damage or kill what you spray it on. Salt is not good for the soil or the plants in it, so overspraying is not recommended. If you have pulled the weeds and still see a few weeds before you plant, spray the leaves and plant.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.