The impact of No Mow May on pollinator numbers and turfgrass quality

The impact of No Mow May on pollinator numbers and turfgrass quality

E. Nangle D. Petrella T. Morris S. Cusack

Introduction:

No Mow May is an effort to increase pollinator number and diversity in homelawns focused on not mowing a lawn through the month of May. The idea originated in the United Kingdom and gained momentum in the United States after work published in Wisconsin (Del Toro and Ribbons, 2020) (now retracted) indicated potential benefits from this practice. Creation of areas that have greater amounts of flowering has been shown to increase pollinator levels (Blau and Isaacs, 2014; Billeisen et al., 2022) alongside maintained areas but the theory that simply not mowing a lawn will have the same effect has to date been untested. The objective of this particular trial was not to evaluate pollinator diversity but rather evaluate simply pollinator numbers as well as the impact of the practice on a home lawn and there were multiple hypotheses, firstly a traditionally maintained homelawn will not see any increase in pollinator numbers, the impact on the lawn through the summer may lead to undesirable effects and finally there may be difficulty in returning the lawn to its previous condition upon completion of the period.

Materials and Methods:

The trial was carried out on three different sites, two located in Wooster OH and one located in Columbus OH. Treatments were initiated on approximately on Apr 28 when all sites were mowed to a uniform height of 3″ and marked out. Plots were set up in a randomized complete design at all three sites with four replications per sites. Treatments consisted of a variety of mowing regimes throughout the summer period including the limitation of mowing during the month of May (Table 1). Plots were 10ft x 5ft in size to allow for commercial mowing decks to pass across the surface with a 5ft border around all plots and between reps. Prior to initiation of treatments treatments were evaluated for color (1-9 scale 6=acceptable 9 = dark green 1 = brown/dead), turf density (1-9 scale 6 = acceptable 9 = no soil visible 1 = bare soil 6 =acceptable), Weed cover (percent of plot), Pollinator count (5min timed counts occuring between 12-4pm on a date prior to the trial, during the trial and at the end of the trial). Turf height was measured using a laser height measurement tool (Bosch) and this occurred at trial completion.

Mowing was resumed on June 2 (Wooster) or June 5 (Columbus) and regimes were installed in regard to how a return to a desired 3″ mowing height would occur. Mowing in Wooster used

Table 1. Treatments used during trial evaluating impact of No Mow May on pollinator numbers and turfgrass quality

Treatment

1 June 1– Mow plot back to previous height – 3” and remain mowing biweekly at this height for 2 months

2 June 1 – Mow Plot back to 5” June 15 Mow back to 4” June 29 Mow back to 3” mowing biweekly at this height for 2 months

3 June 1 – Mow Plot back to 5” June 15 Mow at 5” June 29, Mow at 4”, July 13 Mow down to 3” and continue at this bi weekly until trial completion

4 Mowing maintained throughout the period of May at 3” height and continued through rest of trial period biweekly

5 June 1 – Mow plot back to 4” June 15 – Mow back down to 3” mowing biweekly at this height for 2 months

Results:

Climatically it was a dry period of the year that the evaluation occurred. The monthly rainfall amounts for Columbus were 0.3″ below normal while the area was considered to be abnormally dry. This impacted turfgrass growth by limiting the amount of biomass that was accumulated. On average however in the plots that received no mowing there was a height 16″.

Wooster Maintained lawn data

Turf density and color showed some variability in Wooster on what might be considered a traditionally maintained home lawn and once conditions became warmer and drier later in the trial all plots exhibited declines in color. On the final rating date treatments 2 and 3 showed a significant loss of color (Table 2) compared to all other treatments. Density ratings were much above acceptable during the trial for all treatments until D56 after initiation when a return to mowing and increased temperature lead to a decline in turf density (Table 3).

Table 2. Daily color ratings (1-9) during evaluation of impact of No Mow May on turfgrass and pollinator numbers during Summer 2023 in Wooster, OH.

Treatment	D0	D28	D41	D56	D67	D81
1	7.4 a†	6.1 a	6.6 a	6.5 a	5.8 a	5.9 a
2	7.4 a	6.5 a	6.5 ab	6.1 b	3.9 b	4.4 b
3	7.4 a	6.3 a	6.6 a	6.3 ab	4.1 b	4.1 b
4	7.5 a	6.1 a	6.1 b	6.3 ab	5.8 a	5.5 a
5	7.4 a	6.6 a	6.4 ab	6.3 ab	4.4 ab	5.5 a
LSD	0.4	0.5	0.5	0.3	1.4	0.9