What is horticultural sand and how do you use it?

There is no one product called horticultural sand. Green sand is a mineral that is mined from the ocean which contains nutrients. Red sand can be used to help the soil be more porous and drain better. Diatomaceous earth cuts up soft bodied insects that crawl over it.
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Related Videos:
Use Red Sand in Your Garden: Get Better Drainage
Amendment

Related Resources:
Greensand as a Soil Amendment
Organic Matter and Soil Amendments