To kill moss, it must be actively growing. Late spring/early summer or late summer/early fall, when the weather is warm but not hot, is the ideal time to apply a moss killer, but do not apply the product to newly seeded lawns until after three or four mowings.
When summer heat hits, many gardeners worry about watering their lawns when the sun is shining. The idea behind this is that water droplets act as magnifying glasses, focusing the sun's energy and burning the blades of grass or leaves underneath. However, water cannot cause leaf scorch -- meaning it's time to put the magnifying glass theory to bed.
Watering, Heat and Sunshine
When grass showcases dead spots, the reason is never water droplets baking in the sun, according to horticulturalist Linda Chalker-Scott, PhD, in an article for Washington State University's website. Heat may cause your lawn to yellow, but that means water is the remedy. Waiting until the sun has gone down to water your lawn prolongs the grass's suffering in the heat, and watering close to nightfall encourages fungal development.
Real Watering Problems
Drought and salt buildup in the soil can cause the lawn to die, and both of these issues are related to water intake. When grass doesn't receive enough water, you'll spot patches of dead yellow blades. Meanwhile, fertilizers leave salt in the soil, and if you don't flush the lawn with fresh water on a regular basis, those salts build up in the soil. Other times, water sources have traces of salt in them; this is especially true of urban or arid areas. An excess of salt in the soil can cause root burn or make it difficult for your lawn's roots to absorb water. However, these problems are not related to water droplets on grass in the sun.
When to Water
Rather than settling on blades of grass as scorching magnifying glasses, water droplets evaporate quickly when the sun directly hits them and heat is high. To avoid this evaporation, water your lawn in the early morning. However, if you notice your grass is under drought stress in the middle of the day, water right away to prevent lawn death or disease. In other words, don't let the sun scare you from watering your lawn when it's at its thirstiest.
A simple way to tell if your lawn is experiencing drought stress is to walk across it and check for footprints. If you see footprints, the grass needs more water. Grass that's under drought stress also wilts or curls and turns bluish-gray in color instead of its usual vibrant green. Still, it's healthy to allow grass to go dormant at some point during the year. For cool-season grasses that turn green during the rainy winter, summer is a time for them to go dormant -- and that means leaf blades will start to brown.