Answer: Since you are doing this on a commercial scale you might wish to consult with your county extension (727-7850) for advice, especially since they should be familiar with local market conditions and requirements as well as the least expensive materials available locally. The soilless mixes are made of a variety of materials but may include bark, pine fines, peat moss, perlite, vermiculite and sand or grit. The concern from nurseries is most likely twofold, one that the soil be pest and disease-free, the other that the watering requirements be fairly standardized due to the consistency of the potting mixes. You will also find that the largest scale growers do adjust their mixes to match the optimal growing requirements for different plants. This can include the pH and nutrients of the initial soil preparation as well as the drainage conditions each plant prefers. You may find some information at the following searchable site http://plantfacts.ohio-state.edu/ which includes crop specific production recommendations as well as several discussions of potting mixes and large scale container growing. Good luck with your expanded line!
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