Many of you have heard about this push to participate in "No Mow May." This project is based on the theory that when you stop mowing your residential lawn grass, many more plants will be able to pop up, bloom, and support your local native pollinators. In reality, this is a great way to ruin your lawn.
This project was started by an organization in the UK called Plantlife: Take part in No Mow May - Plantlife. We all need to think carefully about what type of ecosystem we live in and decide whether it's really appropriate or not. While there may be some places in the US where this effort could have some value, the Mid-Atlantic is NOT one of them.
Many American lawns have been treated with herbicides (by you or previous owners) to prevent weed and crabgrass growth, promoting the monoculture of European lawn grass everyone thinks should be the goal. Yes, your "Kentucky Bluegrass" seed is from Europe. If you do have "weeds" growing in your lawn, they are likely exotic weeds. When you stop mowing, these weeds get an opportunity to get themselves further established and probably send out some more seeds. The definition of a weed is a plant that you DO NOT WANT to grow where it is growing. Let's not give them a foothold.
Also, it seems kind of silly to me to expect native plants to suddenly appear in your lawn where they have never existed before. They don't exist in your seed bank. What's a seed bank? Glad you asked.
Everyone has a "bank" of seeds in their soil. These are seeds that are just waiting for the right conditions to germinate. Some seeds can stick around for decades and still germinate given the right light, water, etc. It's one reason we no longer recommend tilling to prep a garden bed. Seeds get into the seedbank by being dropped by plants, birds, and other wildlife, or they can be blown in by the wind or even washed in by stormwater. Here in the Mid-Atlantic, we've had hundreds of years of European seed deposition plus agricultural activity. If you live in a typical residential area, the seeds in the seed bank are primarily exotic weed seeds, not native plant seeds. "No Mow May" gives these guys a chance to proliferate.
One more reason to NOT stop mowing in May: It's very damaging to the lawn grass you want to keep healthy. Ideally, you should never cut more than 1/3 of the length of your grass off at a time. I recommend keeping your mower fairly high (I go with 4") and cut it when it reaches about 6". Every time the grass is cut, it shocks the plant a bit. The more you cut off, the more shock it experiences. This results in slower growth AND shallower roots. I don't know about you, but I have to mow every 5 days in the spring. That's 6 mows during May, cutting off at least 12" of growth. If you wait and cut that much off all at once at the end of May, the shock is quite likely to kill off most of your grass. If you're ever trying to kill off some grass, give it a try.
So what can you do instead of "No Mow May?"
Take proper care of the grass you have, allowing short, innocuous weeds to come in as they please. Clover never hurt anyone, and the bees do use it. Admittedly, I still can't with the dandelions, but they are harmless.
Reduce the amount of lawn you have to the minimum - how much of it do you actually use? Less mowing year-round is great for the environment. Replacing lawn with plants that can be used by wildlife is even better.
Set a goal of 70% native plant biomass in the rest of your landscaping, being sure to include early season bloomers like Violets, Columbine, and Golden Alexander. Violets are perfect plants for the lawn, BTW.
UPDATE!! April 5, 2024
For some reason this post is getting a lot of attention right now, so I thought I'd add a few more thoughts. Those European weeds that are blooming in your lawn during May... do you know what pollinators they support? Particularly that clover everybody loves so much? Honeybees. Not native bees. European honeybees.
No Mow May only works if you live far enough North that you would normally not be mowing in May anyway, you already have native plants that would be blooming in May growing in your lawn, and those plants have time to set seed before they do get mowed down.
You know who else thinks No Mow May is a bad idea? Benjamin Vogt of Monarch Gardens. Check out his blog post here: Just Say No to No Mow May - Monarch Gardens