Fertilizing Lawns

Lawns really benefit from fertilization at least once a year with nitrogen-containing products to maintain turf density, shade out weed seedlings and prevent runoff. If you only do it once, it is best to do it now, between Labor Day and Indigenous Peoples’ Day on October 10. 

Apply no more than one pound of actual nitrogen per 1000 square feet this fall. The ‘N’ (nitrogen) number on the label of your product indicates the percent nitrogen in the product. You will need this number to calculate the amount needed to apply one pound (or less) per 1000 square feet of lawn. There are online fertilizer calculators, such as this one from the University of Missouri: http://agebb.missouri.edu/fertcalc/  – just type in the percentage N in your fertilizer product and your square footage of lawn to calculate the amount to apply. You will also need to calibrate your fertilizer spreader to spread the fertilizer evenly over the area. You can find the free publication A2306 ‘Calibrating and using lawn fertilizer and lime spreaders’ at https://learningstore.extension.wisc.edu/ ; just type the publication number or title into the search box. 

For conventional lawn fertilizers: select one with at least 25-50% slow release (insoluble) nitrogen—this information is on the bag. Avoid blends with high rates of quick-release (soluble) nitrogen that won’t stay in the soil long, especially in areas with sandy soils or high water tables to prevent the product from contaminating groundwater. While grass grown in sun needs one pound of nitrogen per 1000 square feet; turf in grown in shade only needs one-half pound of nitrogen per 1000 square feet, because it isn’t growing as vigorously. Don’t add more to grass in shade thinking it will get you stronger turf, because it will just result in weak lush growth that is more susceptible to diseases like powdery mildew or rust. 

For organic lawn fertilizers: keep in mind that they contain less soluble nitrogen, and soil micro-organisms must break them down to release the nutrients, unlike conventional soluble products where nutrients are available right away. You may also need to apply organic products more often during the season to get the same results as conventional products as they are less concentrated. However, a great benefit to organic products that conventional fertilizers don’t have, is that after roughly 10 to 20 years of use, organic nitrogen accumulates in the soil, so lawns start to need less fertilizer. You can also reduce the amount of fertilizer you need to apply annually by up to one application per year by leaving clippings on your lawn when mowing—lawn clippings make great organic fertilizer and they are free! 

Resources: Visit https://learningstore.extension.wisc.edu/ and type ‘A3958’ into the search box for a publication titled ‘Organic and Reduced Risk Lawn Care’ and scroll down to the red box marked ‘download’ to read and/or print it out. It has suggestions for organic/reduced risk products for lawn fertilization and tips on how often to apply them. Visit https://learningstore.extension.wisc.edu/ and type ‘A2303’ into the search box to view a publication titled ‘Lawn Fertilization’ with more information on conventional lawn fertilizers.

Upcoming Classes: For more information on lawn care techniques, we have an upcoming live online class through our Green Thumb Gardening series called ‘Lawns and Turf Management’ taught by UW-Madison specialist Doug Soldat on October 24. You can register for the class here: https://www.eventbrite.com/e/green-thumb-gardening-fall-2022-registration-391075546487 . If you missed the live class, you can still purchase the video and handouts through our office.

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