Humboldt Nutrients Master A&B is a premium two-part fertilizer program designed for all plants made with non-toxic, high quality ingredients. The Master A&B series stands apart from your standard base nutrient line by making macro and micro nutrients more available to your plant.Master A&B can be used by the indoor and outdoor home gardner for all varities of plants, such as flowers, vegetables, herbs, trees, berries, shrubs, annuals and perennials. This two part system must be used togeather, Part A N-P-K: 4-0-3, Part B N-P-K: 1-5-6