Idaho Lawn Care Calendar — 2026

January is a full-dormancy month for Idaho lawns. Cool-season grasses like kentucky-bluegrass, tall-fescue, fine-fescue have stopped active growth and are protected by snow cover or mulched leaves. Avoid foot traffic on frozen or frosted grass — the blades are brittle and will leave footprints that stay visible into spring.

February remains a planning month in Idaho. Service your mower (sharpen blades, change oil, replace spark plug), check irrigation valves, and order seed if you plan to overseed this year. The lawn itself needs no attention.

March is when the Idaho lawn-care calendar truly begins. Pre-emergent herbicide should be applied during the window of late April in Boise; early to mid-May in the north. Missing this window is the single most expensive mistake homeowners make — the crabgrass, goosegrass, and annual bluegrass seed bank in Idaho soils will germinate the moment soil temperatures cross 55°F for three consecutive days, and once those weeds are up you cannot stop them with pre-emergent this season.

Spring timing in Idaho can vary by 3 to 6 weeks from the north of the state to the south — use your local soil temperature reading rather than a calendar date to trigger pre-emergent and first fertilizer applications.

April is the month cool-season lawns in Idaho fully wake up. Green-up is underway and the grass is resuming active growth. Apply pre-emergent herbicide at forsythia bloom if you did not apply in March, and start mowing once the grass reaches 3 inches. Do not fertilize yet — wait for consistent growth in May. Last-frost dates across the state: April 25 (Boise), May 5 (Twin Falls), May 10 (Coeur d'Alene).

Spring timing in Idaho can vary by 3 to 6 weeks from the north of the state to the south — use your local soil temperature reading rather than a calendar date to trigger pre-emergent and first fertilizer applications.

June is peak growing season in Idaho. Lawns are at maximum density and should be mowed weekly — or every 5 to 7 days for fast-growing Bermuda. Water deeply once or twice per week to encourage deep roots rather than shallow daily sprinklings. Aim for 1 to 1.5 inches of water total per week, including rainfall. If you see ruts from the mower, the soil is too wet to be mowing on.

Idaho watering guidance: irrigate deeply and infrequently (1 to 1.5 inches per week total, including rainfall) rather than lightly and daily. Deep watering drives roots down; shallow watering keeps them at the surface where they dry out in the first heat wave.

July is a survival month for cool-season lawns in Idaho. kentucky-bluegrass and related cool-season grasses naturally slow or enter summer semi-dormancy when daytime temperatures stay above 85°F. Raise the mower to 4 inches, stop fertilizing until fall, and accept some browning. Dormant grass is not dead — it will recover in September. Do not overseed or aerate in July.

August is planning month for Idaho cool-season lawns. Order seed for September overseeding, plan aeration with a core aerator rental, and scout the lawn for bare spots that need re-establishment. The lawn itself is still in summer survival mode and needs no fertilizer. In Idaho, the overseeding window opens September.

September is the single most important lawn-care month of the year for Idaho cool-season lawns. Aerate and overseed on the same day, September. Apply the fall starter fertilizer at overseeding. Fall roots develop more rhizomes and tillers than any other season — lawns that are fall-overseeded outperform spring-overseeded lawns every year for density, disease resistance, and winter survival.

Sharpen your mower blade before the final mows. A dull blade shreds rather than cuts, leaving fringed tips that brown out and give disease a foothold over winter. Clean cuts heal quickly even in cooling weather.

October is winterizer month across Idaho. Apply the winterizer fertilizer in October — a fertilizer with higher potassium than nitrogen — to build cold tolerance in the grass crown. Cool-season lawns are growing hard in October; mow weekly and continue removing leaves as they fall. Heavy leaf litter on wet grass will smother the lawn.

If you have not done a soil test in three years, October is a good month to pull samples and submit them to your state Extension Service. Results come back in 2 to 3 weeks and will tell you exactly what to apply next spring.

November is the end of the active lawn-care season in Idaho. Do your final mow at 2 inches — not shorter, which exposes crowns to winter damage, and not taller, which mats down under snow and encourages snow mould.

December is a fully dormant month in Idaho. No mowing, no fertilizing, no watering. Clean and store your mower for winter. Dormant grass is easily damaged by foot traffic on frozen mornings — keep off the lawn when frost is visible on the blades.