Q & A: Fall Lawn Care

September 25, 2017

by Sam Bauer

Q: What mowing height should I keep my lawn at before winter?

A: Generally we suggest to keep your lawn at the same height as you’ve had in the fall.  Cutting the lawn short prior to winter has been commonly suggested in the past as a means of reducing spring damage from snow molds and voles, but cutting the lawn too short will be more of a stress to the grass than the injury you may experience from diseases or critters.  If the standard mowing height for your lawn is 2.5 to 3 inches, we suggest to keep it at that.  If the height is 3+ inches, then we would recommending bringing it down to 3 inches before winter.  If you do plan to lower the mowing height, be sure to mow several times at this height, not just the final mow.  The goal is to condition the grass to this new height with several mowings prior to winter.  Again, we may only suggest this if you have had snow mold issues in the past or if you maintain your grass at a long height in the fall.  Also, be sure to continue mowing until the grass stops growing, this will help reduce snow molds and winter damage.  You can use a bagging attachment on the last mow of the year to help remove any excess organic matter and leaf litter.

Q: Should leaves be raked off of the lawn or mulched with a mower?

A: It depends.  For homeowners with numerous trees, it may be impractical to mulch all of them into the lawn without smothering the grass at some point.  In that case we would suggest mulching a majority of the leaves into the lawn and raking up the rest.  Be sure you can see at least 80-90% grass after mulching leaves, this will ensure that the leaves aren’t smothering the grass.  To practically mulch all of your tree leaves, you may need to be out with a mower more often than your grass needs to be cut, because if too many leaves fall, you may not be able to mulch them into the lawn.

Tree leaves contain organic matter and many nutrients that can be beneficial to your lawn.  For example, a study conducted in New Jersey on 100 municipal trees demonstrates nutrient content of 1% nitrogen, 0.1% phosphorus, 0.38% potassium, also secondary macro nutrients and micronutrients.  The organic matter will also benefit the lawn by increasing moisture holding capacity and improving aeration.  Standard mowers will work, and we suggest to close the side discharge for mowers that have one.  Closing the side discharge will contain leaves in the mower so they get chopped up better before they fall into the grass canopy.  Mulching blades can be purchased as well.

Here are some resources that help to further explain leaf mulching:

WCCO Good Question: Do we really need to rake?

Minnpost: Leaf bagging under scrutiny as a wasteful expense and pointless chore

Q: Is it too late to fertilize my lawn?

A: No.  For Twin Cities residents, we suggest to fertilize by mid-October at the latest so there is a little time left.  However, be sure not to fertilize past mid-October.  New research on late-fall fertilization demonstrates that a majority of the fertilizer applied in late-fall (late-October or early-November) can be lost to the environment because lawn grasses are not able to absorb fertilizer as well when temperatures are low.  Here is more information on our recommendations:

Upper Midwest Lawn Care Calendar for Cool Season Grasses

Fertilizers and the Lawn Care Program

Q: Can I seed my lawn now? 

A: No, late September is usually not a good time.  The best time to seed a lawn in the Twin Cities is mid-August to mid-September.  Germination that occurs later than this time frame is bad and seedlings will generally die if they haven’t matured.  However, dormant seeding later this fall is an option.  Dormant seeding is the practice of seeding when temperatures are too low for the seed to germinate prior to winter, and it is expected that the seed will germinate in the spring. This can give you a jump on spring seeding. 

Q: When should dormant seeding be done?

A: Sometimes it is a bit of a waiting game. The trick is to find the time when soils are unfrozen so that seed can be worked in slightly, yet air temperatures must be cold enough so the seed won’t germinate. Wait for high daytime temperatures of 35-40 degrees before seeding, which usually do not occur until November. Here is more information on dormant seeding lawns:

Dormant Seeding Lawns: Last chore of the season