Two part nutrients are split in to two separate containers usually called A&B. Each part is comprised of specific macro and micro nutrients that combine to form the NPK ratio. Plants require specific macro and micro-nutrients in order to thrive. Two-part nutrients separate minerals which would otherwise bind together forming sediment in the bottle. These minerals can become bound up and unavailable to plants. Keeping these nutrients separate in their concentrated form ensures that 100% of the minerals are available to your plants. See Understanding 2-Part Nutrients to learn more.