Often, soil already has enough nutrients from the previous year’s fertilizers and grass clippings. In that case adding more fertilizer will not help the grass.
Soil nutrient testing can be performed by Cornell Cooperative Extension of Suffolk County to measure the amount of nutrients in the soil, and determine whether fertilizer is needed
Fertilizer is typically only needed on lawns if the density of grass is low and soil is visible. If the lawn density is high, no fertilizer is needed.
In Suffolk County, it is illegal to fertilize lawns between November 1st and April 1st. Fertilizing during that period can result in a fine of $1000.
Fertilizer should be added to lawns in the late spring and/or early fall. These times of the year are periods of high growth for the grass, the better time being early fall so the grass can best prepare for the winter.
During periods of high temperatures and low rainfall, usually during the summer, grass goes into a dormant state and slows growth and fertilizer should not be added to lawns during these conditions as it will not likely be used by the grass, and instead will be wash into groundwater.