Ask the Master Gardener: No Mow May not necessarily the right way

Not mowing in May means not mowing until June, which could mean the grass is anywhere from 12-18 inches high. Mowing more than a third of the plant’s tissue in a single mowing can stress a lawn.

A person mowing grass.
If you want to promote pollinators in your lawn for the month of May while ensuring a healthy and resilient lawn, mow as high as your mower will allow and only as needed to avoid mowing more than one-third of the height.
Contributed / Metro Newspaper Service

Dear Master Gardener: Is No Mow May a good idea to protect pollinators and is it really a good idea for the lawn?

Answer: We definitely want to protect pollinators in our gardens! You bring up a good question about what it does to the lawn. There has been a No Mow May movement for the past few years to promote flowers for early season pollinators. This movement was first promoted by a research paper that has since been retracted. Here is what turfgrass experts at the U of M have to say:

Minnesota lawns are typically made up of several cool-season turfgrasses. Not mowing in May means the lawn is not mown until June, which could mean the grass is anywhere from 12-18 inches high. There would be so many grass clippings that you would have to compost them, rather than leaving them on the lawn, which is best practice. In addition, mowing more than one-third of the plant’s tissue in a single mowing event is known as scalping, which can stress a lawn. If you want to promote pollinators in your lawn for the month of May while ensuring a healthy and resilient lawn, the U of M recommends mowing as high as your mower will allow and only as needed to avoid mowing more than one-third of the height.

If you are interested in a bee lawn, the University of Minnesota has great information at this website: .

Dear Master Gardener: Could you give us an update on Emerald Ash Borer please? Has it reached the Brainerd lakes area?


Answer: Emerald ash borer is a very serious invasive species that has killed millions of ash trees. It is a small, iridescent green beetle that attacks and kills both weak and healthy ash trees. The larvae live underneath the bark of ash trees and their tunneling kills the tree. Minnesota has almost one billion ash trees so the spread of emerald ash borer will have a devastating impact on our forests. Crow Wing and Cass counties are not affected yet. So far (according to the Minnesota DNR) emerald ash borer has not been found north of St. Cloud, except the greater Duluth and Fargo areas.

Dear Master Gardener: I have had a cherry tree for three years. This year the dear ate the lower branches and the rabbits ate the bark. There are buds on the tree. Is it going to make it? Something also ate a lot of the bark from my serviceberry. Is it a goner?

Answer: Rabbits, voles, mice and deer can cause a lot of damage to trees and shrubs during the winter, especially winters with scarce food and extended snow cover. They feed on trees and shrubs and can severely damage or destroy plants. If a rabbit or vole removes the bark completely around the trunk of a tree, it has been girdled. Girdling disrupts the flow of sap from the tree’s foliage to the root system. All growth above the girdled areas will eventually die, so unfortunately the tree will need to be replaced. According to Iowa State University, most deciduous shrubs are able to produce new shoots or suckers from the base. Because of this ability, many severely damaged deciduous shrubs will eventually recover, although it may take several years. For a damaged shrub, prune off girdled stems just below the damaged areas in early spring. Prevention is the best way to manage these pests by protecting your shrubs and trees in the fall.

Dear Master Gardener: This has been the worst year we have ever seen for snow mold in our lawn. What should we do?

Answer: As the snow melts, many homeowners are discovering patches of snow mold in their lawn. Gray and pink snow mold fungi are the most common — you will usually see gray or pink patches that have matted grass within the patch. Gray snow mold produces white to gray colored mycelium and pink snow mold produces off-white to pink colored mycelium. Both types are active at temperatures around freezing and under wet conditions. Snow molds are most common when an early, deep snow cover prevents the ground from freezing, which is exactly what happened this year. Don’t worry — damage caused by snow mold is rarely a serious problem. It will probably take these areas a little longer to green up this spring. To avoid further fungal growth, you can gently rake the affected areas of lawn to help it dry out, but wait until the soil is dry enough to handle foot traffic. To lessen the severity of snow mold next year, avoid excessive nitrogen fertilization after the middle of September because it can lead to succulent grass tissue that is conducive to the growth of snow mold. In addition, mow until the grass is no longer actively growing. Tall grass is more likely to mat down and encourage the development of snow mold. Raking up all the leaves will also help. Snow molds are not common every year — this was an unusual year with early, heavy snowfalls. A preventative fungicide application in the fall is generally not recommended.

Dear Master Gardener: Is Filipendula a good perennial to add to a part sun garden bed?

Answer: Filipendula (meadowsweet) is a striking addition to the full sun or light shade garden. They are easy, long-lived perennials that are rarely bothered by disease or insects. Most of the Filipendula develop into bushy plants with bold foliage and tall flowering stems. Filipendula rubra (Queen of the Prairie) makes a statement in the garden with its 60-inch height and large, feathery plumes of pink flowers. Venusta is a cultivar with darker pink flowers. Filipendula ulmaria (Queen of the Meadow) is shorter, ranging in height from 30-48 inches, depending on the cultivar. The plumes of this variety are creamy white. Filipendula vulgaris (Dropwort) is more tolerant of dry conditions than the other varieties. Multiplex is a cultivar that has double creamy white flowers and is 18 inches in height. There is a dwarf Filipendula hybrid called Kahome that is 12 inches in height with rosy pink, fragrant flowers. All of them are hardy to zone 3.

You may get your garden questions answered by calling the new Master Gardener Help Line at 218-824-1068 and leaving a message. A Master Gardener will return your call. Or, emailing me at and I will answer you in the column if space allows.


University of Minnesota Extension Master Gardeners are trained and certified volunteers for the University of Minnesota Extension. Information given in this column is based on university research.

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