Probably not many. It's a cat litter bag made of weird paper, it will degrade quickly and it smells like cat litter chems that I would not want touching my plants. If you are just doing seeds, I would use those plastic pre-washed lettuce trays that you buy from the grocery store (with big holes poked through the bottom), and with flat trays or something beneath to hold the water. They are great.

No chem odour with these, but I get your point. I haven't seen the lettuce trays you mentioned around here. Mostly I was just hoping to kill two birds with one stone - use up these bags and have something for short term seed starting since I'm out of pots and flats. I may try some non-edibles in one just for grins. I'm deep in the throes of spring fever and the rainy weather won't cooperate!

If a straight clay litter with no scents, I imagine you could use the bags safely enough. I would avoid any that use a "fresh scent" or baking soda or the like. If the bags are paper, they will degrade quickly. Other materials like plastic would be more durable.

FataMorgana

These bags are either heavy plastic or maybe plastic coated paper I think

If you are just starting your seeds in them I have used the styrofoam boxes I get mushrooms in. I just put several slits in the bottom with a knife for drainage.