Agree, use top-shelf for teas. I would suggest using fewer high quality castings and skip the cheap ones. Add some compost which will feed the microbes added in the quality castings.
If planting in soil, add 1/8 inch of worm castings at the bottom of the hole or trench, the seedling will find the castings when they are ready for them. When soaking seeds in water add just a pinch of worm castings to the water.