Effect of "Now Mow May" and "Leave the Leaves" on Lawn-Height Turf

In the past few years there has been a push to encourage homeowners to not mow their lawns for the month of May, otherwise marketed as "No Mow May". The movement was started in the UK to support or increase pollinator populations. Pollinators need sources of food in the spring after wintering and the idea is that the lawn can provide this food through the flowering weeds such as dandelions. This movement has made its way into Ontario and is being pushed by conservation authorities and environmentalist movements. However, we theorize that No Mow May can be harmful to the home lawn - possibly increasing the presence of undesirable weeds and eventually leading to homeowner frustration and dismay.

Another campaign that has been gaining traction is "Leave the Leaves". This campaign echoes the sentiments of No Mow May, with the additional suggestion that leaves should be left untouched on the lawn surface to provide overwintering niches for pollinators and other beneficial insects. However, too much leaf cover could lead to smothering and death of the turf. Dr. Paul Koch at the University of Wisconsin is conducting a trial this fall on different depths of leaf cover (5 cm or 15 cm, mulched or not-mulched) to test effects on snow mould, turf quality, and soil health over the next few years. 

Researchers have shown that lawns participating in No Mow May had greater pollinator diversity and abundance to mowed urban green spaces (i.e. parks) (Del Toro and Ribbons, 2020). That research project is one of the only published experiments that supports the concept of No Mow May and yet it has serious shortcomings regarding methodology and potential conclusions. The comparison of home lawns to parks is not valid comparison because home lawns typically have more diversity than parks, due to their close proximity to flower beds, flowering trees, and hedges. A better comparison would have been to compare lawns participating in No Mow May to lawns that were not. 

In a new study at the Guelph Turfgrass Institute, we will be observing lawn-height turf (60% Kentucky bluegrass, 20% chewings fescue, 20% perennial ryegrass) which has been treated with 2.5 kg of Norway maple leaves (mulched or not-mulched, approx 5 cm depth). Turf quality, weed encroachment, and disease pressure will be evaluated next spring. In the spring of 2023, half of these plots will be left UN-MOWED until June 1st. We expect to see a significant decrease in turf quality for the plots covered with leaves, and we might see an effect of fertilization from the mulched leaves. We will report back on the effect of No Mow May practices next year. 

This project is made possible through the Knowledge Translation and Transfer partnership with Landscape Ontario.
Research by Dr. Sara Stricker &. Dr. Eric Lyons

Visit https://uoguel.ph/TurfReports to access archived and current research reports from the Guelph Turfgrass Institute.