Watering grass seed in the sun can cause damage. While some will still sprout, there are several key risks to consider before taking this route.
First, seeds require moisture to germinate and ample exposure to sunlight accelerates growth. However, direct sunlight greatly increases evaporation rate. Without proper care, newly planted grass can dry out too quickly for proper absorption of water or nutrients.
Second, the sun’s heat can scorch the delicate foliage of young plants. In some cases, direct exposure to sunlight in combination with drought-like conditions may lead to stunted or burned grass patches that are difficult to repair.
Third, high temperatures and intense light increase weed competition because weeds thrive due to accelerated growth rates under such conditions. To ensure that your lawn has a head start on weed management efforts, water sparsely and away from direct light whenever possible.
Finally, soil compaction is a common issue caused by excessive foot traffic and machinery when the soil is wet. By avoiding overwatering due to excess heat or insolation during daylight hours you help ensure that your new lawn isn’t damaged while it takes root and begins to spread over time.
Water seed only when necessary; preferably in late afternoon or night where available humidity lessens losses due to evaporation and heat wilting of the fragile shoots emerging from the ground.