A PK booster (AKA "Bloom Booster") is an organic or synthetic fertilizer designed to be used during a plant's flowering growth state. A true PK booster only contains phosphorus and potassium. On the other hand, a base nutrient fertilizer contains all the micro and macronutrients useful for all plant growth stages. The PK Booster works by activating a change in a plant that "boosts" the plant into the flowering stage quicker, which results in a plant having more time for flower growth. And more time for flowering means bigger and better flowers and fruit.