In May, many bees are coming out of hibernation and need flowers to feed themselves and their babies. The main purpose of No Mow May is to encourage people to let spring flowers in their lawns bloom before mowing. Flowers you can commonly see blooming in lawns in May include dandelions, white clover, and creeping charlie. While many people view these flowers as weeds, some pollinators view them as food. Ideally, you can add to the mix and provide food for more pollinators by adding native plants. Early spring blooming native plants like violets and pussy toes can be a part of your bee lawn. Plant diversity is key to supporting bee diversity, so if you can, plant a wide variety of native spring blooming flowers, trees, and shrubs, like pussy willows, serviceberries, and bluebells. For blooms in your lawns after May, add self-heal, ground plum, lanceleaf tickweed, or calico American aster.
Although we all get anxious to clean up in the spring, hibernating pollinators often need a bit more time under the leaves before they can safely emerge. Leaves left on the ground provide important insulation for bees hibernating underground and for moths and butterflies that overwinter in the leaves. Leaving your leaves where they are until temperatures are above 50 degrees F for 5 consecutive days will give most of those hibernating pollinators the protection that they need. Bees that nest in stems may not emerge until mid-June or later. It is best for the bees to leave the stems where they are. New growth will soon cover them, any bees nesting in the stems will emerge, and the old stems will decompose. If you want to remove past seasons' stems from your garden before mid-June, find a place to safely stash the cut stems until the bees that might be nesting in them have a chance to emerge. Come midsummer, you can safely compost these stems. When you do cut stems back, leave about 12 inches of stem standing to create nesting habitat for this summer's bees.
Can we thatch our lawn before May?
It depends on why you are deciding to not mow in May. If it is to let flowers bloom in your lawn, then it is probably better to get rid of the thatch so any flowering plants in your lawn have more room to grow. That thatch could be making nesting habitat for some bees, but you would need to leave it there longer than May to make a difference for those bees. If you have an out of the way corner in your yard where you can make a pile of thatch, that could make great habitat for some bees.
Will mowing in May harm overwintering rusty patched bumblebees?
No. Rusty patched queens dig themselves down into the soil several inches to overwinter and are most likely to do that in places that are more protected than your typical lawn. If a rusty patched queen does happen to dig a hole to overwinter in someone's lawn they would be about 2 inches underground and not likely to be impacted by mowing. There are other bees, such as miner bees, that do overwinter and even make nests in lawns. They are underground and are not affected by mowing, even when their nests are active. These are extremely gentle bees that don't sting even when you are messing with their nests.
Won't not mowing in May just encourage invasive weeds to spread?
People should not take the catch phrase "No Mow May" literally. The basic idea of No Mow May is to increase the availability of flowers. For example, if you give dandelions a chance to flower, but mow before they go to seed, you can provide resources for pollinators and not increase their spread. That mowing to prevent seed spread may need to happen during May. For white clover, you may need to mow in May to encourage them to flower again if the flowers are going to seed. Encouraging native plants that flower in lawns is a great solution to the problem of invasive weeds in lawns. Some people may still consider these plants to be "weeds" but they are simply flowers that grow where grass used to grow.