For newly planted grass seed (including newly overseeded lawns), water twice daily so that the top half inch of the soil always remains moist. Stop watering when puddles begin to appear on the soil surface (about 10-20 minutes, depending on irrigation/water source). Once the seeds germinate and grass seedlings begin to grow, gradually transition to watering less frequently but more heavily. Taper off watering as the grass becomes taller and more mature. Do not mow the lawn until the new grass is at least 3 inches high, and then follow the Lawn Maintenance instructions below.
For hydroseed lawns, allow the mulch to fully dry (about one day) and then proceed with the above watering instructions for traditional seeding. Water 2-3 times throughout the day, depending on weather, to keep the mulch moist at all times.
Water sod immediately after installation. For the next two weeks, water 1-2 times per day, about 1" per cycle, checking to make sure soil beneath turf is wet. A small corner can be lifted to check soil below, and then tucked back into place. Reduce watering if puddles form or footprints are seen when walking on turf. Signs of underwatering are wilting or straw-colored sod, or if cracks are observed between the pieces of sod. New sod can be mowed about 1 week after installation. Avoid using the lawn until good root establishment has taken place, about 2-3 weeks for normal traffic and 4 weeks for rough usage.
Once the lawn is established, water as needed to supplement rainfall so your lawn receives about 1 inch of water per week under normal conditions. (Measure the sprinkler water you collect in 15 minutes to determine how long it takes to supply 1 inch.) Water the lawn between 4am-10am whenever possible, as early morning watering reduces loss to wind and evaporation, and allows water to soak in before sunlight heats the soil. For best results, never cut more than 1/3 of the grass blade per mowing and maintain sharp mower blades.
Water new shrubs and trees at the root ball immediately after planting, and every day for two weeks. From 3-12 weeks, decrease frequency to 2-3 times per week, and then once a week beyond 12 weeks until roots are established. Always monitor moisture in soil, especially during hot dry periods, and add water if soil is dry to touch. Watch for signs of overwatering (soft, droopy and/or yellowing leaves) or underwatering (dry, light and/or yellowing leaves). When watering newly planted trees, in general, 10 gallons of water is needed for a 20"-24" rootball, which is equivalent to 1" rainfall.
Umass Extension Turf Program
Umass Extension Landscape, Nursery, and Urban Forestry Program