A. No, for two reasons. One is that garden soil can contain insects or diseases that could harm plants in containers. Growing media for containers is sterilized, so any potential bugs have been eliminated. Secondly, potting mix for containers also contains drainage material like vermiculite or perlite, and it's composed of materials like peat moss and bark which are lightweight, consistent and allow for good drainage. Garden soil in a container will soon compact with all of the watering that is required, and your plants will suffer from a lack of oxygen to their root systems. Garden soil may be cheaper because it's already available, but it will cost more in the long run than using a good quality planter box soil.