Home Lawn Care Newsletter | May 2023

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Welcome to the latest issue of the Home Lawn Care Newsletter from UMN Turfgrass Science! We will provide up-to-date information to address all your lawn care tasks at the times when you need to know.

a lawn mower in a yard

May 15, 2023: Issue 11

The best way of reducing mowing? Mow higher and only when needed

Most people with lawns would love to reduce the amount of time they spend mowing. There is a way to reduce time spent mowing that also reduces the amount of time watering and eliminating weeds.

The key is letting your lawn grow taller - to a height of between 4.5 and 6 inches. Then when mowing, cut no more than ⅓ of the blade, bringing the height to between 3 and 4 and inches. Maintaining this height reduces stress on the plant, and encourages tillering and thickening the grass stand. Research shows that when mowing following the ⅓ rule, 8 mowings per year can be eliminated. That can be as much as 31% of your mowing time.

Lawns mowed at these heights will also shade the soil, keeping it cooler while reducing evaporation. This can mean less watering and deeper root growth. Mulching or recycling the clippings as you mow returns nutrients to the lawn. Not only does leaving clippings benefit the lawn, it reduces bags of clippings that are sent to a landfill. One last benefit of shaded soil is that weed seeds won’t receive the sunlight they need to germinate. Maintaining mowing heights by taking no more than ⅓ of a blade at a time will help you use less water and use less herbicide and fertilizer. Saving time is the added bonus.

Should I use a weed-and-feed product?

Weed-and-feed products combine fertilizer and herbicides and are designed to make life so much easier - they are ready-to-use, you get two treatments for the price of one, and applying once is much less work! So why wouldn’t you want to use a weed-and-feed product?

The primary reason weed-and-feed is not particularly effective is because timing the application is difficult. For example, pre-emergents take 5-7 days to take effect. They must also be watered into the soil prior to seed germination in order to properly disrupt the root or shoot growth. Since crabgrass germinates when the soil has been an average of 55 degrees over 3-5 days, choosing the right date for application is challenging.

Some weed-and-feed products contain a post-emergent in addition to pre-emergent.
Broadleaf post-emergents are most effective when applied to actively growing weeds, slightly later than a pre-emergent would be applied. Rather than spot-treating specific weeds with a product intended for them, the entire lawn receives a treatment that may not be needed with a weed-and-feed strategy. Additionally, both pre-emergent and fertilizer should be watered into the soil. Broadleaf treatments need to stay on a plant, and should not be watered immediately after application. Broadleaf post-emergent products such as 2,4-D or Dicamba that are applied as granules and reach the soil can cause severe, unintended damage to shrubs and tree roots. We obviously want to limit adding chemicals to the environment when they are not effective and can cause harm.  
If you’ve ever used a weed-and-feed with poor performance, these reasons may explain why. What really saves you time and money is applying chemicals when they will do the most good and you can use the least amount of product. If you know you’ve had heavy infestation of weeds, and you’ve identified the weed and know the right product for treatment, apply a stand-alone pre-emergent that addresses just the weeds that need treating. If you haven’t had weed problems, don’t apply it. Rather than a broadleaf post-emergent that’s part of a weed-and-feed, spot treat any weeds that appear with the appropriate post-emergent spray treatments, following label instructions. You can target specific plants, and protect areas of pollinator-friendly plants, shrubs or trees from unintended exposure.

Wait until after the first mowing to put down fertilizer if the lawn is looking sparse. Follow UMN Extension’s guide for determining how and when to fertilize. This can provide necessary nutrients at the right time and thicken the grass to out-compete weeds. In the long run, you’ll save money by only applying exactly what you need at the time it’s most effective for a healthy, attractive and environmentally friendly lawn.

With all fertilizer applications, ensure that you are following Minnesota’s Phosphorus Lawn Fertilizer Law. Do not apply phosphorus containing fertilizers to lawns unless you have a recent soil test showing that the soil is deficient in phosphorus, or that you are establishing a new lawn.

Seeding a lawn with pre-emergents already applied

‘Tis the season for pre-emergents. What happens when you’ve applied the pre-emergent and then decide to overseed some spots that aren’t greening up? Spring-applied pre-emergents prevent weedy seedlings like crabgrass, but they don’t affect weeds that have already emerged. They work by being soaked into the soil and establishing a barrier. When seeds germinate, the germinated seeds pass through the pre-emergent barrier, which impacts the seed’s ability to grow roots or shoots.    

Pre-emergents may impact your turfgrass seeds too, so it’s typically recommended to avoid seeding turfgrass in your lawn for 3 to 5 months after applying pre-emergents. Fall seeding cool season grasses is the best option if you have already applied a pre-emergent this spring. If you need to seed small areas after applying a pre-emergent, disturbing the area by removing and replacing the soil with new topsoil is an option.

Start thinking about your irrigation system

Whether you’ve just moved into a new home, or want to reduce the amount of water you’re using when you run your sprinklers, now is still a great time to ensure your irrigation system is operating efficiently. You can save a significant amount of money by making sure your irrigation system is not leaking, is covering the right areas, and is providing the appropriate amount of water for each irrigation event. To find out more, check out our instructions for completing your own irrigation audit and our other irrigation resources. Consider updating to a new irrigation controller. Check with your local water utility (this could be your city) who may be offering an irrigation control rebate through a grant from a local or other agency such as from the Metropolitan Council.

Research highlight

Help needed with Japanese beetle research

3 images, the first is beetles eating a rose flower, the second is three white grubs of varying sizes and the third is a plastic hanging trap

Japanese beetles are a damaging pest of turf and landscape plants. The Krischik lab of the University of Minnesota is conducting research on Japanese beetle management with a native, soil inhabiting pathogen, Ovavesicula popilliae. We know the pathogen can be found in Stillwater and the UMN St. Paul campus. We are trying to locate other places where the fungus might be present.

Our team is looking for Twin City residents that will allow us to set up Japanese beetle traps on their property to determine if Ovavesicula popilliae is present. Every 2 weeks, traps would be set up and removed after 24 hours from July through September.

Please fill out this short survey so we can learn more about Japanese beetle issues in MN. Also, indicate whether you are interested in being a cooperator with us. We will call you if you want to join us. 

If you have questions about participating in this research, please contact Dr. Vera Krischik ([email protected]) or Michael Angstman ([email protected]). 


We will be at these events to answer questions on smart irrigation and lawn care as part of our collaboration with the Metropolitan Council.


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