Make sure you buy a mix, not a soil. Mixes are sold by the volume (i.e., 2 cu. ft), not by weigh also, it should state it's for containers or not for containers)t. The fertilizer in it may not be enough to sustain a plant (such as a vegetable) through the season, so be ready to put in some 10-10-10 (for instance) fertilizer. If you are growing tomatoes, mix a bit of dolomite limestone in with the mix to help prevent blossom end rot (the dreaded BER). Good luck.
Weedbreeder