you add 2 TSP per gallon on soil when mixing ( i.e. 2 parts Fox Farms Ocean Forest, 1 part Happy Frog, 1 part Chunky perlite, 2 TSP mycorrhizae, 2 TSP dolomite lime ).
there's your new soil recipe. The mycorrhizae add beneficials to your soil and roots.
If you already have plants growing in soil, then make 4 holes about 2" deep around the perimeter of the pot, add 1 TSP mycorrhizae to each hole, cover the hole with soil and water as usual.