(5) 13 gram size capsules for large trees. These water-soluble gelatin capsules are a convenient way to deliver multiple species of plant growth promoting (PGP) soil microorganisms to a tree or shrubs root zone. BioCaps contain a special formula designed to promote improved plant and soil health, and generate impressively robust growth in shrubs and trees.’ Get to the Roots BioCaps can be applied to shrubs and trees of all sizes. Apply 6 inches down into the soil at the drip line (where water runs off the leaves or needles). Reapply every six months, preferably in spring and fall. Extra capsules may be applied to stressed plants or trees.