you wanna use soilless potting mix to promote very good drainage which is the most important factor in growing plants. regular garden soil is too heavy ( even some potting soils that contains soil) some people makes their own blend and very small portion of garden soil can be mixed in the soilless mix but i prefer just mixing compost with soilless mix about 20% to give some life to it.

potting mix vs. garden soil. it's not that one is better than the other, they are just different medium for different use. why is garden soil cheaper? actually good garden soils are not that cheap. there are many bad quality garden soil that's sold . many of them i found it just sad. some of them are straight up dirt/cement, some are like clay smelling like a sewer.... if anyone... ever have to buy garden soil i advise to just buy one bag and exam what they are like first before you commit to many numbers. check the organic material content, what it's made out of, smell... differend brands have completly different content in it and definition of what " soil" is. i guess it's the same with pottin mix. although it's not as diverse as top soil/garden soil, they can be quite different brand by brand and some are much better/worse than the others.

Thankyou for explaining, i got miracle gro potting soil and so far it is good, only little expensive as i have to fill a couple of 5 gallons.
Nila