Top soil is straight, screened soil with no additives to improvethe quality for planting. It is recommended to be used as a base under planting mix because it is less expensive and compacts better.

Planting mix is "amended" soil made by mixing humus, soil and sand. It is ideal for planting. Because it doesn't compact well, it is advised to put a base of top soil under the planting mix.

-- Tips courtesy of HomeAdvisor.com