Ask the Master Gardener: Mowing a lawn too short could harm the grass

Taller grass shades out weed seeds and helps shelter the crowns from heat and wind, protecting them from excessive drying. There is evidence that roots grow deeper when grass is taller.

A lawnmower mowing grass.
Don't mow your lawn too short and leave grass clippings on your lawn.
Contributed / Metro Newspaper Service

Dear Master Gardener: I am a new homeowner and have never taken care of a lawn. What is the best practice to maintain a healthy lawn?

Answer: To keep a lawn healthy mow at the proper height and leave the grass clippings on it. Try to maintain a height of 3 inches or higher, but mow before the grass reaches 4.5 inches tall. Taller grass shades out weed seeds and helps shelter the crowns from heat and wind, protecting them from excessive drying. There is evidence that roots grow deeper when grass is taller. When you mow, don’t remove more than one-third of the leaf tissue. Mowing too short will cause stress to the grass plant and allow weed seeds to get more sun and germinate. Leave the grass clippings on your lawn. Leaving decomposed clippings on the lawn adds the equivalent of one fertilizer application to your lawn each year, improves soil quality, minimizes runoff, and improves carbon sequestration. Make sure your mower blades are sharp because cleanly cut grass blades are able to conserve water and decrease the need for irrigation. Dull blades cause jagged edges making the grass plants more susceptible to diseases.

Dear Master Gardener: When do I pinch back my late-blooming perennials to get them bushier?

Answer: Pinching does produce a fuller plant and most tall or thin plants can benefit from pinching. Pinching refers to removing a small amount of growth, usually less than 1-2 inches, from the tip of the shoot. To make tall asters more compact, simply pinch out the tip of each stem to force more side branching every few weeks, starting in late spring or early summer. The newer cultivars of mums do not need to be pinched. The traditional method is to pinch out the tips on side branches when they have grown 6 inches and continue pinching until mid-June to early July, depending on the bloom time of the variety. Pinching the tall growing sedums to four inches may prevent flopping.

Dear Master Gardener: My neighbor recommends a natural weed killer using dishwashing detergent, vinegar and Epsom salts. Good idea or not?


Answer: Not! There is nothing natural about it — look at the ingredients list for dishwashing detergent! Vinegar and Epsom salts are both chemicals and neither one is good for soil health. Vinegar will kill the leaves of weeds, and anything else it lands on including beneficial insects and amphibians, but doesn’t kill the roots, so most of the weeds will be back in about a week. Concoctions that have not been tested and labeled as herbicides are technically illegal and should not be used. Fully tested commercial herbicides, used in the correct amounts and with proper application, are actually cheaper, more effective, and safer for you and the environment.

June Garden Tips

  • Early June is a great time to finish planting gardens, containers, and hanging baskets. 
  • Move houseplants outdoors when nighttime temperatures are 55-60 degrees, as they will benefit from increased light and humidity. Keep them protected from direct sun. Heat and wind can dry them out, so check them often to see if they need water. Add fertilizer at half-strength every few weeks.
  • Cut rose flowers early in the morning when it is cool and the top of the bud is starting to open. Make the cut at a 45-degree angle above an outward-facing, five-leaf leaflet with sharp, clean pruners.
  • You may need to replace early vegetables such as peas, radishes, leaf lettuce and spinach with quick maturing seeds or transplants. You can direct seed green beans (bush type), beets, green onions, or summer squash.
  • Water your lawn deeply and infrequently when it shows signs of drought stress (dull color, blades curling inward, your footprints are obvious in the grass). Conserve moisture by watering early in the day when temperatures are lowest and winds have not picked up yet. Avoid late evening watering if possible because foliage that remains wet overnight is more prone to plant diseases.
  • If you need to prune spring-flowering shrubs, such as rhododendron, azalea, lilac, forsythia, weigela, or ninebark, do it right after they have finished blooming. Pruning later in the summer may eliminate much of next year’s blooms.
  • Anthracnose is a fungal disease that shows up almost every year on ash, maple, and sometimes oak trees. It causes large dark blotches on leaves, many of which drop. Only rarely is it severe enough to damage trees. Rake up and dispose of fallen leaves.  Fungicide is not necessary.
  • Resist the temptation to cut or pull off or tie together the unattractive leaves of daffodils, tulips, and other spring-flowering bulbs. Leave them until they are no longer green.  Keep fertilizing until they are brown and withered because the foliage continues to gather energy to nourish the bulb for next year.
  • Cut back Dicentra (bleeding heart) as the flowers fade. This will reduce reseeding and encourage new growth.
  • Avoid overfertilizing your plants. Most perennials get all the nutrients they need from the soil. Top-dress established beds every three to four years by working several inches of compost into the soil surface. If plants are stunted or less vigorous you can give them a boost with a diluted solution (one-half the recommended amount) of liquid fertilizer.
  • Check the upper and lower leaves and stems of your plants for aphids and mites. They suck out plant juices and cause leaves to turn yellow and brown. Spray leaves, especially the undersides, with a blast of water to dislodge these pests. If there are still too many, use an insecticidal soap (a soap formulated to kill soft-bodied insects that is not harmful to the plant or environment).
  • Check pine trees for pine sawfly larvae that look like caterpillars. Knock them off with a blast of water from your garden hose.
  • Create a butterfly garden with children by planting butterfly favorites: chives, butterfly weed, coneflowers, liatris, yarrow, dill, zinnia, marigold, verbena, and/or cosmos. Add a few rocks for sunning and a shallow saucer of water. A book your children may enjoy is “Where Butterflies Grow” by Joanne Ryder and Lynne Cherry.

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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