The answer to 'when to lawn fertilization' is that the best times to fertilize your lawn are in the spring and fall. In the spring, apply a slow-release fertilizer in early to mid-April to help your lawn green up and grow thick. In the fall, apply a fertilizer in late September or early October to strengthen the roots and prepare your lawn for the winter ahead.
Fertilizing your lawn 2-3 times per year, in the spring and fall, is generally recommended for a healthy, lush lawn. The specific timing can vary depending on your climate, grass type, and other factors, so it's a good idea to consult with a local landscaping professional for guidance on the optimal fertilization schedule for your lawn.