Laguna Plant Grow Fertilizer Pond Spikes supply important nutrition to aquatic plants for a period of up to one year. The temperature-activated feeding sticks release nutrients only when plants need them most � at or above 50� F or 10� C. Once activated, the spikes slowly release a well-balanced feeding formula that maximizes the size and colour of aquatic plants. With low amounts of phosphorous and no copper, the pond spikes have no adverse effect on water quality and are non-toxic to fish and plant life. The Plant Grow Fertilizer Pond Spikes are specifically designed for potted plants and are compatible with all planting baskets. Length of spike : 18 cm (7 in). Quantity : 3-pack.