Answers to Common Fall Lawn Care Questions

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Adam Thoms
Assistant Professor and Turfgrass Extension Specialist
Iowa State University

Every year we seem to get the same questions from the public on lawn care, specifically this time of year when people are disappointed in how their yard held up. While not all of these questions will fit your yard, some of them might. It is our goal that these points help address those questions, and give the knowledge to have a successful growing season. Good luck!

Question: Is it ok to skip the fertilizer in the fall?

Raking leavesAnswer: Fall fertilization is the most important step to help your yard for next year. Nitrogen taken up this fall will be converted to carbohydrates for the next growing season, or it will be used to help drive root growth this fall. A deeper root system will help keep the plant alive through the summer stress and drought. Ideally you should apply ½ to 3/4 lb. of nitrogen per 1000 sq. ft. to your yard in September and again in late October or early November.

Question: When should I seed my yard?

Answer: Seeding a yard or overseeding should be done between August 15 - September 30 of each year. Grasses planted during this period often have less disease pressure to compete with, and summer annual weeds like crabgrass and goosegrass are done germinating and won’t compete for space and nutrients. Fall established yards also have a longer period to mature before the heat and dry periods that the summer growing season brings.  

Question: When should I try to control my broadleaf weeds?

Answer: After the first frost is best for control of the weeds. Frost kicks in a response in plants to take whatever they uptake, and move it to the growth point. This increases the effectiveness of most broadleaf herbicides to eliminate a higher amount of broadleaf weeds. You also will want to spray with a herbicide containing several different chemicals in it to increase the control of the various weeds in the yard.

Question: What should I do to the crabgrass in my yard right now?

Answer: Crabgrass, goosegrass, and foxtails are all warm-season annual grasses and will die with the upcoming frost. At this stage in the growing season you would have to apply a herbicide three times to try to get the weed to die, and the frost might be what actually kills it first. Your best control of these weeds would be to apply a preemergence herbicide in the spring to prevent them from germinating.

Question: I don’t want to use herbicides, what can I use?

Answer:  Every year there are new products on the market that claim to control weeds in yards, however independent research is often lacking on these products or the products can actually harm all living tissue and not just weeds. Corn gluten meal is an example of a natural product that has been shown through independent research to control weeds. An application of corn gluten meal in the fall and spring can help lower weeds in your yard over time. It will not happen overnight, but will take several years. There are also many iron-based products, which with repeated use, can help control some weeds.

Question: My yard was great 20 years ago, what happened?

Answer:  Most often your yard has gone from a sunny yard to a shady yard in that time. That is a long time for trees to grow and fill out, changing the sun light present in your yard.  Kentucky bluegrass does really well in full sun, but not very well with shade. You may need to start adding some fine fescues or perennial ryegrass to your yard each fall. You can also trim the tree limbs up to allow more light onto the yard to help it.

 Question: What height do I need to mow my yard, and can I mow it lower in the fall?

Answer: We would like to see most yards mowed at around three inches tall. If you are getting plenty of rain (around an inch per week) and the temperatures are cooler like in the late fall, you can drop the mowing height to 2.5 inches. The taller the grass the deeper the roots, so keep mowing heights tall to help drive deep roots.

Question: How often should I mow?

Answer: Never remove more than 1/3 of the leaf tissue in a single mowing. So if you want to keep your yard at three inch height of cut with the mower, you should mow when the grass reaches four inches. It is always better to keep your mowing height taller, as it lessens how often you need to mow to avoid violating removing more than 1/3 of the tissue in a single mowing. Mowing is a stress, so the fewer times you mow the less stress you are putting on your yard.

Question: What should I do with the leaves on my yard?

Answer: Get a mower with a mulching blade and recycle them into the yard. Make sure you mow over the leaves so that they are small enough to fall down into the turf canopy and not smother the grass. This may mean mowing two directions over the yard to get the leaves down into the turf canopy.

Date of Publication: 
September, 2019