Mixing Sand With Earthworm Castings

I grow my own wheatgrass at home. I am using an organic compost but was wondering, after having read an article, if it's ok to use earthworm castings mixed with a little sand?

Here at Gourmet Greens we have been growing wheatgrass commercially for almost 30 years and have always grown it the old fashioned way with soil containing earthworms that naturally deposit the earthworm castings directly into the soil. Why don't you put your mix to a test? If the wheatgrass grows vigorously with a deep green color, then the earthworm castings mixed with a little sand is most likely ok to use at home as a growing medium.