mixing store soil with existing soil

anyone know the ratio that I could get away with? I was thinking even parts existing ground soil, with store bought soil? so 50/50?, I have very little cash, anyone have an idea, I guess it all depends

like you said......it all depends on the existing soils quality and what kind of soil you want to mix with it.

Mix some perlite with the soil.

Dude, I am growing veggies to experiment, and the best low ratio is 20% good soil/80% dirt from my yard, but my soil is well ph'ed naturally!