Then plan to plant it during the ideal conditions. Cold air and soil temperatures prevent germination so avoid sowing grass seeds in winter as it simply wont germinate. Watering New Grass Seed A Caution And A Guide Grass Seed Seed Germination Seeds As your new grass seed grows and flourishes you can water deeper and less frequently this will encourage established grass roots to extend deeply into the soil. How long should i water grass seed . Sprinkler Irrigation System Tips. Once the grass is a few inches tall you can stop watering as consistently and depending on how hot it is water can be given every 2 or 3 days. Water once per day for 2 -3 days before planting the grass seed. When there is a lower chance of evaporation due to sunlight and wind. Seeds and very young plantsgrass usually need water twice a day. The type of grass seed youre using and when is also a huge variable in how long. 15 hours agoOther seeds especially bent and meadow grasses can take up to...