Bob Mugaas, UMN Extension Educator
Even though much of the month of October can be one of the best times for grass growth and recovery, it's tempting to put away our thoughts, practices and equipment used to care for our lawns by the middle to end of September. The reason for this active period of growth is that the lawn grasses adapted to this area (e.g., Kentucky bluegrass, the fine fescues and perennial ryegrass) are best adapted to the cooler and usually moist conditions of spring and fall. See Picture 1. So, with that in mind, here are a few end-of-season lawn care practices that help support actively growing grass plants.
1. Mowing. So long as our grasses continue to grow, we should be continuing to mow as needed. With cooler temperatures and shorter days, mowing intervals usually become longer the later we go into the month. A common question at this time of year is "Should I cut my lawn shorter the last mowing of the year?" One reason to consider somewhat shorter mowing heights in the fall is the decreased (usually) incidence of snow mold come the following spring. Longer matted grass potentially creates more favorable habitat for the snowmold fungus to live and grow over winter. We see the results of that fungal growth the next spring when, as the snow melts and retreats from the lawn surface, the lawn appears covered with grayish or pinkish colored patches indicating the presence of snowmold.
However, reducing the height of a lawn should not be something reserved for only the last mowing. For example, if the lawn has been kept at about 2.5 - 3.0 inches during the growing season and the desire is to reduce that to two inches, then begin the process of gradually lowering that mowing height two to three mowings prior to your very last cutting. That will help the grass adjust to a lower height of cut more gradually instead of being scalped just before going into colder conditions; a more stressful condition for turfgrass. If the grass is still actively growing during October, you may need to mow somewhat more frequently in order to reach and then maintain the lower mowing height. This is because shorter heights of cut require more frequent mowing to establish and maintain them.
2. October is the month when leaves drop from our deciduous (leaf losing) trees. The spectacular fall colors of early October give way to leafless trees ready to face the winter months ahead. So, what to do with all of those leaves? A small amount (usually less than a couple of inches) of fall leaves can be left on the lawn surface and ground up with a rotary mower. Be sure to go over them several times such that the remaining leaf particles can more easily sift down into the lawn and soil surfaces. The lawn should look like it was raked when you are done. See Picture 2. If there are still piles of shredded leaves be sure to rake them off of the lawn surface and either compost them or use them as a mulch in other parts of the landscape. Leaves can also be removed from the lawn by picking them up using the mower's bagging attachment (if it has one) and redistributed as a mulch cover in another non-lawn part of the landscape or composted.
3. Early October is an excellent time to apply herbicides to perennial broadleaf weeds such as dandelions, creeping Charlie, clover, and plantain. See Picture 3. Where only a few weeds are present, hand removal can be just as effective as an herbicide. On the other hand, weed control products are now widely available in ready-to-use application containers. Hence, we can spot treat the specific weeds while introducing minimal amounts of herbicide to the environment. Where weeds are more numerous and scattered throughout the lawn, a broadcast application of an herbicide product can also be done. These can be applied either as a granular or liquid product. The products used should be weed control products only and not combined with a lawn fertilizer as this would not be a good time to be applying fertilizer. Always follow product label directions exactly - it's the law. Be sure the weeds (and lawn grasses) are actively growing at the time of application as the product's effectiveness will be much better than if weeds are growing under water stress. If necessary, water the area to be treated a day or two the planned application to help ensure their active growth.
4. It hardly seems necessary or even appropriate to be talking about watering a lawn given the amount of rainfall and flooding issues experienced over the last few weeks. Nonetheless, should October turn dry and remain warm, lawn grasses will likely benefit from an additional watering or two before shutting down for the winter. In general, it's a good practice to not have lawn grasses go into winter conditions severely stressed due to lack of water. We don't need to follow the one inch per week at this time of year due to the cooler temperatures and shorter days. Both of those conditions slow the loss of water from the lawn and hence any watering required can be done at longer intervals. In other words, that same one inch of water per week, (including rainfall), during the summer months might be sufficient for two or even three weeks this time of year depending on weather conditions.
5. Finally, new suggestions for applying nitrogen fertilizers to Minnesota lawns no longer include a late October to early November application. In short, new research here at Minnesota and Wisconsin questions the usefulness of that nitrogen application due to the inefficiency with which it's taken up by the grass plant. Hence, the preferred late season fertilizer application time for Minnesota lawns is around Labor Day to the middle of September. Nitrogen absorption is much better at that time of year and it ensures adequate nitrogen nutrition for the grass plant going into a very active period of growth. For more information on this topic see the article in the August 1, Yard and Garden Newsletter.
Continuing through the fall with few important lawn care practices can help ensure a healthy lawn going into the winter months and a healthier lawn to begin the growing season next spring. Good Luck!