It rains all hours of the day, so it is perfectly natural to water a lawn any hour of the day. As a matter of fact, you will not kill your lawn because you watered at the “wrong” time. Two principles rule the life and death of your lawn, regardless of when you water: 1)Your lawn thrives in a moist soil, 2)Your lawn dies in a dry soil. So, the best time to water your lawn is at a time that keeps the lawn moist.
If the time you water is not as important as keeping the lawn moist, then the best time to water your lawn is at sunset. When you water at sunset, the lawn will stay moist longer during the dark, cool hours of the night.
Photosynthesis by Day, Respiration by Night
During the day, plants produce sugars using the power of the sun (photosynthesis). By night, plants use those sugars to grow and reproduce in a process called respiration. And water is the fuel that runs the respiration process – without adequate water, respiration slows dramatically. Keeping the lawn moist all night long promotes growth.
Composting: The Enzymatic Digestion of Organic Matter
A lawn is more than a patch of decorative grass, it is a biological filter – a thriving ecosystem of organisms – including fungi - that are composting organic matter into plant food (compost). Watering in the evening promotes composting. Composting requires moist warm conditions to work and these conditions prevail during the night. The more composting, the more food available to the lawn – the more food, the more growth.
I’ve Been Told to Water at Sunrise to Prevent Fungus
Watering at sunrise is a persistent myth that is even promoted by the Pinellas County Extension Service. The promoters of this myth claim that if you water at sunrise, the leaves will dry out quickly and you will have less fungus. Well, that is not a solution, that is a problem – dryness and less fungus. Your lawn loves moisture and fungi are part of the composting process to recycle dead dying organic matter into plant food.
Evening Watering vs. Morning Watering
When you water in the afternoon, just before or after sunset:
1. Lawn stays moist longer – no sun to dry out plants and soil
2. Plants have plenty of water to grow and reproduce (respiration)
3. Optimum for Composting
When You Water in the Morning, just before or after sunrise:
1. Lawn dries quickly – less water day and night
2. Lawns will struggle all night with little water to grow
3. Dry conditions prevent fungus and other organisms from composting
Your Mileage may Vary
Like fisherman over the best time to fish - some believe you catch more fish at low tide, some at high tide – gardeners will disagree on the best time to water a lawn. For me, I found that after an evening rain or watering, my lawn always looked fresh, green and ready for the day. Not so much for watering in the morning.