Treasure Valley lawn guide
How often to water your lawn in Boise and the Treasure Valley
Our summers are hot and dry, and most of the valley gets very little summer rain, so irrigation does nearly all the work. The goal is deep, infrequent watering that grows deep roots.
How much water per week
- Spring and fall: about 1 to 1½ inches per week, including rain (University of Idaho Extension).
- Mid-summer: needs climb higher in July and August heat; many Treasure Valley lawns need roughly 1½ to 2 inches per week (estimate, varies by soil and exposure).
- Late fall: taper off as growth slows and nights cool.
How often
Water deeply two to three times a week rather than a little every day (estimate for typical clay-loam soils). Deep soakings push roots down; daily sprinkles keep roots shallow and invite disease.
Clay soils take water slowly. If water runs off, split each watering into two shorter cycles an hour apart (cycle and soak).
Best time of day
Early morning, roughly 4 to 8 a.m. (estimate), loses the least to wind and evaporation and lets blades dry during the day, which limits disease.
Measure, don't guess
- Set a few tuna cans on the lawn, run one zone for 15 minutes and measure the depth to learn each zone's rate.
- Push a screwdriver into the soil: if it slides in 6 inches easily, the root zone is moist.
- Footprints that stay pressed down or a blue-gray tint mean the grass is thirsty.
Common questions
Does pressurized irrigation change the schedule?
The water need is the same, but pressure irrigation usually runs only during the irrigation season and may have set watering days. Check with your district or HOA.
Should I water a dormant brown lawn?
Bluegrass can survive summer dormancy if it hardens off first. If you let it go dormant, give it about half an inch every two to three weeks to keep the crowns alive (estimate).
Related LawnWise guides
Sources
- University of Idaho Extension CIS 1098 — Watering Home Lawns and Landscapes
- University of Idaho Extension — Lawn and turf
Figures marked "estimate" are LawnWise rules of thumb for the Treasure Valley, not extension data. Updated 2026-10-30. By LawnWise, from Seljaas & Sons LLC, Middleton, Idaho.