Blossom Blaster 1 Kg, Grotek. Grotek Blossom Blaster (0-39-25) is a powerful blend of phosphorous and potassium fertilizers designed to increase the number and size of blooms. It contains a very high concentration of phosphorus and potassium which contribute to proper plant maturation, fruit quality and the formation of sugars, starches and oils. Because Blossom Blaster is such a powerful flowering supplement, it only needs to be added twice during the first 3 weeks of flowering. Be sure to add a fresh nutrient solution. Blossom Blaster is effective in all growing media and is compatible with all base nutrients. Use only 2x during flowering cycle. Use only with change of nutrient.