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A Challenging Summer for Turf Areas: What Now?
The set up: Experienced managers know that the turfgrasses best adapted to this region are in the category of cool-season grasses. These species experience their best growth when air temperatures are in the range of approximately 60-75 degrees F, and when soil temperatures are proportionally lower, 50-65 degrees F.
The key cool-season grasses also vary genetically at both the species and variety levels in their ability to perform under moisture deficits. At the species level, grasses like tall fescue or fine fescue are more drought resistant, widely-utilized species like Kentucky bluegrass and perennial ryegrass are in the moderate range, and more thirsty, shallow-rooted grasses like creeping bentgrass and annual bluegrass have generally poor drought resistance. Management plays a role as well; for example, lower mowing heights result in proportional reductions in root mass, which translates to lower overall drought resistance. Weather, of course, also factors in very heavily; for example, grasses will use more water more rapidly under elevated temperatures, breezy conditions, and low relative humidity.
Thus, the typically high temperatures and below-average precipitation of the “meteorological summer” months of June, July and August create the most stressful period for our otherwise well-adapted cool-season grasses. The summer of 2022 has certainly been no exception, with predominantly above-average temperatures, including a 4-day heat wave to close out July that was quickly followed by a 6-day heat wave during the first days of August. These excessive temperatures have co-occurred with muted precipitation inputs that may rival our most recent notable drought season (2016) when things are said and done. This has left approximately 38% of Massachusetts classified as D3 (“Extreme” drought) as of this writing, with an additional 56% classified as D2 (“Severe” drought) according to the U.S. Drought Monitor (https://droughtmonitor.unl.edu(link is external)
). The entirety of Massachusetts is currently under official drought status.
Cool-season grasses have evolved the capacity for dormancy in response to these seasonal extremes. Dormancy is another way of saying “survival mode”, and substantial reductions in both appearance and function of turf come with the territory. As dormancy progresses, the turfgrass plant essentially retreats to the crown (the principal plant growing point at the soil interface) and, under extended dormancy, virtually the entire shoot and root system can die back. As long as the crown remains viable, however, re-growth is possible when more favorable conditions return.
What determines whether the crown remains viable? Most of it comes down to water and carbohydrates… these are the main currencies of the plant. The crown must maintain some minimal level of moisture to stay alive as well as a store of carbohydrates sufficient to support recovery when conditions moderate. The precise elements that influence how long a plant may survive under dormancy are many and include length of dormancy, degree of dormancy, plant genetics, prevailing weather both prior to and during dormancy, management practices, and turf use.
A rough rule of thumb is the longer that dormancy continues and the more severe the summer weather, the smaller the percentage of plants that will recover adequately. Pests, traffic, and other abiotic factors can also kill fragile crown tissues when plants are in a dormant state, and dormant turf is far less competitive against encroaching weeds.
Where do we go from here? The saving grace is that the ideal period for planting occurs immediately after summer stress, from late August through September. In the case of existing turf areas damaged by drought, there two basic approaches to re-establishing the turf on a site:
Renovation (less disruptive) – Process of replacing the turf plants on a site without making changes to the soil or grade. Does not normally include total removal of existing turf, but usually includes eradication of the existing stand with non-selective herbicides, extended covering, or mechanical defoliation. May include light cultivation in the interest of promoting seed-to-soil contact.
Reconstruction (more disruptive) – Involves wholesale removal of existing turf on a site in conjunction with tilling or other soil cultivation, at least to the depth of the root zone or deeper. Frequently also includes addition of soil amendments, addition of topsoil, and/or changes to grade.
If renovation compares to remodeling an out-of-date kitchen, reconstruction is like rebuilding the whole house. Renovation is most appropriate when turf has deteriorated but the soil and overall growing environment remain generally suitable. A general guideline is to renovate when 50% or more of the turf is composed of undesirable grasses or weeds. Renovation is also a great opportunity to match grasses more closely to site conditions and future management objectives.
When there are ongoing problems that go beyond just the plants present, a full-scale reconstruction may be warranted, but any decision to take on a reconstruction project should be carefully considered. In modern medicine, for example, there is an effort to better tailor patient treatments to precisely fit the severity of the condition. When health problems are dire or life threatening, there is more opportunity to gain from major intervention. When issues are less severe, however, major intervention may be less appropriate because there is smaller opportunity for benefit. In other words, the risk of net harm is increased when the degree of intervention is greater than what the problem truly requires.
Decisions to ‘open’ the soil in a turf system, as is the case with reconstruction projects, should always be approached cautiously. Cultivating soil can damage soil structure, introduce the possibility of soil erosion, and stir the ‘seed bank’. At the same time, cultivating the soil provides opportunities not typically available in a perennial turf system including ability to incorporate fertilizer and soil amendments, improve drainage, and alter the grade. In other instances, opening the soil may be required to remove boulders or buried debris, or to install physical infrastructure such as irrigation system components. Therefore, in most circumstances, complete reconstruction should be based on identifiable need or, from a strictly agronomic perspective, treated as a last resort.
Compared with renovation, reconstruction is more expensive, time-consuming, labor intensive, and functionally and aesthetically disruptive. When circumstances or budget do not permit a justifiable reconstruction, a renovation approach will most often yield measurable improvement. Even in situations where the means and need for reconstruction exist, opting for renovation first may at best have satisfactory results and at least buy some time (perhaps multiple seasons) before the larger investment of funds and energy in a wholesale reconstruction project.
Door number three for post-summer tune-ups is seeding into an existing, living (or partially living) stand. Overseeding involves seeding into established turf in the interest of repairs or maintaining adequate density. Late summer is also a great time for interseeding, as part of a plan to gradually introduce different grass species or cultivars and alter the stand composition over time. A fantastic way to accomplish this is with power slice-seeding equipment; a less sophisticated method is broadcasting seed after cultivation practices such as core aeration.
For more details on planting and selecting the best establishment approach, refer to UMass Extension’s Best Management Practices for Lawn & Landscape Turf, Section 5, Establishment, Renovation & Repair.
How can I improve a situation for next time? In non-irrigated scenarios, planting heat and drought resistant grasses will mean better performance and lower tendency for dormancy for under summer stress. On irrigated sites, heat and drought resistant grasses will save water. Heat and drought resistance among species was already detailed above, but there is also much variation within species. Poring over producer or University data to identify grasses with positive water use traits can be tedious; thankfully there are a few notable University and industry groups that do this work for you. Look for these seals of approval on seed products: A-LIST, which is the Alliance for Low Input and Sustainable Turf (http://a-listturf.org/(link is external)
), the Turfgrass Water Conservation Alliance (https://www.tgwca.org/(link is external)
), and even the EPA Water Sense program (https://www.epa.gov/watersense/turfgrass-and-water-efficiency(link is external)
)... yes, the same criteria that are applied to all kinds of products like appliances and toilets, are used to qualify turfgrass seed.
The wild card: Remember that adequate and consistent moisture is necessary for successful establishment, renovation, or repairs. This is true for even the most water-efficient grasses that will ultimately be very drought resistant and have low water demands. Because of the adversely dry year to date in 2022, many Massachusetts communities have water restrictions in place that could affect the ability to irrigate and therefore should be reviewed prior to jumping into any planting activities. For complete information on current restrictions, see: https://www.mass.gov/info-details/outdoor-water-use-restrictions-for-cities-towns-and-golf-courses(link is external)
Jason Lanier, UMass Extension Turf Specialist
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