I would recommend never touching the substrate. I never do in any of my tanks. You can read the explanation in my article on bacteria, here: http://www.tropicalfishkeeping.com/f...quarium-74891/
There is a section covering the substrate, but reading the rest of the article will put it in a better perspective for understanding things.
As Inga said, CO2 addition is not required for healthy plant growth. If you read my 4-part article at the head of the Aquarium Plants section ["A Basic Approach to the Natural Planted Aquarium"] you will find that it is all about balance. Light and 17 nutrients must be balanced, and the plants will grow at that level. Increasing CO2 for example creates a new balance, a higher one, meaning more light intensity and more of the other 16 nutrients. Plants will usually grow faster with higher levels, but they will still grow if more slowly and be healthy and performing their filtration tasks with lower levels, what we term natural or low-tech approach.
Baby tears is not an easy plant for many, so if you are growing that successfully without CO2, you have no reason to add it.
And questions are never dumb; success comes with knowledge.