Kentucky Bluegrass & Summer Dormancy

The most commonly used turfgrass for home lawns is Kentucky bluegrass; a cool season grass that performs best under the cool growing conditions of spring and fall. Kentucky bluegrass also has the unique ability, when extended dry conditions occur, to go into summer dormancy. While dormant, the crowns of grass plants are live but existing leaf blades become dead and brown, and no new leaves are produced. Normally summer conditions do not promote turfgrass dormancy until late July, but spring conditions this year have been abnormally dry, resulting in early dormancy in some home lawns.

Summer Dormancy

Allowing bluegrass lawns to fully enter dormancy is an alternative to continued watering during hot, dry conditions and can result in a significant water savings. Actively growing Kentucky bluegrass lawns require up to 1.5 inches of water per week, while a dormant bluegrass lawn requires only 0.5 inches of water every two weeks.

A light watering or rainfall of 0.5 inch every two weeks supplies enough moisture to keep crowns, rhizomes and roots hydrated and alive. While this low volume of water will not re-green a dormant lawn, it will help to insure good recovery once rainfall occurs in fall.

Mower Damage

A problem often seen in drought stressed lawns is the bruising of wilted leaves and shoots during mowing. As leaves go into dormancy their tissues become brittle and are susceptible to bruising by any kind of foot or mechanical traffic.

Bruised leaf blades develop brown streaks or become completely brown. Obvious brown streaks can often be seen in lawns mowed during periods of drought stress. Streaks in the lawn follow the pattern of the mower wheels, which bruised the turfgrass leaves.

No leaf spots, which would indicate a disease problem, are evident. Symptoms disappear in fall when active turf growth resumes.

Protect Dormant Turf from Excess Wear

Avoid excess foot or mechanical traffic on a dormant lawn. Dormant turfgrasses do not generate new leaf blades to replace those that are damaged, so excess traffic causes the existing foliage to break down and wear away. Once the existing foliage is gone, continued traffic begins to injure plant crowns resulting in weakening or death.

Injury does not become apparent until the grass begins to green up in fall. The end result is areas of turf thinning due to death of the plant crowns, along with an increase in weed growth in the open areas. Thin areas may require overseeding to re-establish a dense turfgrass stand.

Protect Dormant Turf from Insect Damage
Dormant lawns are still subject to insect damage, especially from white grubs that feed on the root systems of plants even in the dormant state. If your lawn has a history of white grub injury, it is a good idea to periodically check areas of past grub damage to determine if a problem is developing.

Check for damage by gently tugging a handful of leaf blades. Since white grubs eat grass roots, damaged plants will pull out of the ground easily. If insects are found at a level exceeding 8-10 grubs per square foot of turf, then control is necessary. Lawns with a history of white grubs should receive an application of imidacloprid or halofenozide in late June. If grub damage is not identified until late summer, a late season grub control product, such as Dylox, should be used.

Keep in mind that our other common cool season turfgrass, tall fescue, does not enter summer dormancy as bluegrass does. It stays green until it totally runs out of water then begins to dieback. Do not manage fescue lawns for summer dormancy.