Letting a Lawn Go Dormant in a Montana Drought

Is a brown lawn dead or dormant?

Usually dormant, if it was healthy going in. Iowa State University Extension explains that Kentucky bluegrass survives extended drought by turning brown and going dormant: the leaves die back but the crowns and roots stay alive, and a healthy dormant lawn greens up again once it gets enough water. Colorado State University Extension calls bluegrass's dormancy mechanism excellent, and says many bluegrass lawns can survive weeks, even months, without irrigation.

A quick check: tug on a handful of brown grass. Dormant grass is anchored, and the crowns at the soil line are firm and pale rather than mushy or dry and brittle. If the sod lifts like a loose carpet, the problem may be grubs rather than drought; see our guide to lawn insects in Montana.

Is it OK to let my lawn go dormant in summer?

Yes, if you commit to it. MSU's article on landscaping to reduce water use says the natural cycle for cool-season turf in Montana is to green up in spring, go dormant and brown in summer, and resume growth in fall; irrigation is what breaks that cycle. MSU also notes that landscape irrigation is often the largest household water use and that several communities are adopting irrigation restrictions.

The mistake is going halfway. Iowa State describes two options in hot, dry weather: let the turf go dormant, or water to keep it green and growing. Watering just enough to keep a lawn half green, half brown, waking and stalling over and over, is harder on it than either. Pick a strategy for each area of the yard and stick to it.

How long can a dormant lawn go without water?

Weeks, not the whole summer. Iowa State says most healthy lawns can survive in a dormant state for 4 to 6 weeks without rainfall or irrigation, but that bluegrass will not stay dormant indefinitely and is at risk of dying if dormant for more than 4 to 6 weeks. Its recommendation for a bluegrass lawn that has been dormant that long is to apply 1 to 1.5 inches of water in a single application, then water again 7 days later; the grass should begin greening after the second application.

In western Montana, a dry stretch from early July into late August can easily exceed six weeks. If you choose dormancy, mark the start date on a calendar and plan that rescue watering. Measure what your sprinklers actually put down with a few straight-sided cans; CSU's PlantTalk on efficient watering describes running the system 15 minutes and measuring the depth in the containers.

Which grasses handle dormancy best?

Kentucky bluegrass is the best of the common lawn grasses at it. CSU's turfgrass selection guide lists good drought resistance for bluegrass, specifically that it can go dormant and survive long periods without water. CSU's note on bluegrass drought tolerance observed that more than a few tall fescue lawns were killed or thinned by the same watering restrictions under which bluegrass survived well.

Fine fescues are drought resistant but go dormant (CSU), and can go dormant during extended heat in the 90s. Crested wheatgrass, per CSU, goes dormant quickly in drought but recovers from dormancy rapidly, and MSU lists it with streambank wheatgrass and the bromegrasses as grasses that brown in drought and suit very dry or non-irrigated lawns. Our guide to Kentucky bluegrass versus fescue covers the trade-offs.

Which lawns should not be allowed to go dormant?

New ones and stressed ones. MSU says newly established turf is particularly vulnerable to insects, and young lawns lack the root and crown reserves to ride out weeks without water; a lawn seeded or sodded this year should be kept growing. CSU's note on drought tolerance found that bluegrass lawns that died in drought had mostly been poorly managed before it (poor mowing, fertilization or irrigation), damaged by mites, or planted on poorly prepared soil.

Traffic matters too. Iowa State says dormant lawns should not be mowed, because foot and mower traffic can damage the turf. A dormant lawn that is also the dog run or the kids' field will thin out. Keep the high-use areas watered and let lower-use areas go dormant.

How should I care for a dormant lawn?

Mostly, leave it alone. Do not mow it while brown (Iowa State). Hold off on fertilizer: Iowa State says it is generally not advisable to fertilize cool-season grass in summer, and MSU's Montana schedule puts the key feedings around Labor Day and late fall. Do not spray weeds: CSU says drought-stressed weeds respond poorly to herbicides, and South Dakota State notes these products need actively growing weeds.

Before it goes dormant, mow at the top of MSU's 2.5 to 3 inch range so the crowns are shaded, as our guide to mowing height explains. Keep trees and shrubs watered even if the lawn browns; they are far harder to replace. Our guide to watering trees in drought covers that.

How do I bring the lawn back in fall?

With deep water and then food. MSU says that in most of Montana, bluegrass uses about 1 to 1.5 inches of water a week early and late in the season. CSU's PlantTalk on fall watering says historic data for Colorado show a need of 0.5 to 1 inch of irrigation a week in September and October, and that fall is when turf forms new side shoots and rhizomes to heal after a stressful summer. Start with Iowa State's two deep waterings a week apart and then settle into a regular deep schedule.

Fertilize once it is green and growing again. CSU's note on fall fertilization during drought says feeding a lawn that has been dormant for a month or more provides little benefit that fall, though it can help spring green-up of still-living bluegrass. Our guide to fertilizer rates and timing has the Montana calendar, and aeration and overseeding in early fall fills any spots that did not survive.

What if parts of the lawn do not come back?

Patch them in the fall window. Thin or dead spots after a dry summer are a good time to overseed, since MSU says mid-August to mid-September is the best time to seed in Montana. If large areas died, look at why: CSU's brown spots note says lack of water is the most common cause of brown patches, but mites can also cause brown spots in dry conditions, and CSU recommends watering dry areas in fall and in winter when possible to discourage them. Uneven coverage from a broken or poorly spaced sprinkler often shows up as the same dead strip year after year; see our sprinkler repair service.

Should I keep a smaller green lawn instead?

For many properties, that is the better long-term answer. MSU's article on turf reduction describes converting lawn that does not earn its water into mulched beds of adapted plants, and notes that removing lawn usually means capping or rerouting sprinklers and adding drip to new beds. A small, well-watered lawn where you actually use it, with the rest converted, uses less water than a large lawn kept half alive. Our guide to replacing some lawn with native plants and Missoula's outdoor watering guidelines cover the details.

Do watering rules affect a dormancy plan?

They can. In Missoula, the city's conservation page recommends watering from May 1 to September 30 during 6 to 11 a.m. and 5 to 10 p.m., deep-soaking lawns, and adjusting sprinklers so water stays off sidewalks and streets. Iowa State's rescue watering (one deep soak, then another a week later) fits easily inside those hours. Check your own water provider or ditch schedule before planning around it.

How HJ can help

We tune irrigation systems so water goes where you want green and stays off what you have chosen to let rest, repair the broken heads that create dead strips, and bring lawns back in fall with aeration and overseeding and our licensed fertilizer and weed control program. This guide is part of our Montana Landscaping, Lawn & Irrigation Guide. Call (406) 215-7319 or request a free estimate.

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