The best time for application is early in the growing season. It is better for first year spraying to begin when the weeds and grass start to green up. This will allow for better control of the harder to kill weeds. After the first year of spraying, you can spray earlier the following years. Water or moisture is needed for the product used to be affect. It is harder later in the season to control the weeds if the rain and moisture has lessened or stopped.