Hello Steve, happy to help. Actually, there are two of us who writing to help you out.

Adding organic matter may be of some help for compacted, clay-like soil but it may need much more than what is typically added to fill aeration holes. Stephen H. will probably have more to say about that.

Overseeding in the spring is a good plan especially if you have been successful with that. (Weeds start germinating at the same time and can make it problematic to start lawns at that time.) We can also recommend dormant seeding in late fall which is basically waiting until the ground is very cold to spread your grass seeds so that they won't germinate but just before there's a good cover of snow.

When the snow melts in the spring the seeds are there and ready to start germinating at the optimum soil temperature. Just be sure to water if the ground starts to dry out due to lack of spring rains and you haven't seen any germination activity. Here is more information about dormant seeding.

There are some drawbacks; timing the spread of the seeds so they don't start sprouting now and before it snows, and good snow cover all winter to keep the birds from eating the seeds.

There will be more shortly.  Good-luck!

Thanks for your question.

I will also respond to some of the questions you asked:

1). The no-mow grass seed you used probably consisted largely of one or more types of fescues. The most commonly used is creeping fescue. You would not expect to see any bluegrass. These fescues by their natures are slow growing and while very drought resistant, their growth tends to be very minimal with hot weather.  This is why they are drought resistant. Mowing is often done in the spring and the fall. I think that our very hot season (2021), which started in early summer and extended up to the fall, is why your yard began to look rather thin The turf was largely in a state of dormancy. This is one of the disadvantages of no-mow yards. They just don’t grow well in hot weather but also they do not die off.  For this reason little mowing is necessary in the summer. Depending upon future growing seasons, you may see a repeat of a thin turf with hot summers. These fescues like cool weather. I suspect that your seeding in early summer (2021) might have been too late because hot weather also had set in by that time .See:

https://www.prairienursery.com/resources-guides/about-no-mow-lawn/

2). Since this is a rather new area you are dealing with, I would strongly suggest that you test the soil before doing any spring seeding. This would indicate to you what fertilization, if any, should be done. This analysis would also tell you the composition of the soil and its organic content. My colleague’s comments about aeration and adding organic material are spot on. It’s now getting a bit cold to do that this fall. This could be done in spring 2022. BUT if you do that, do the soil testing first to establish a base line. See:

https://soiltest.cfans.umn.edu/testing-services

3). Mycorrhizal treatment consists of adding fungi to the soil to increase the fertility of the soil. However and this is important, for these fungi to be effective they need to attach themselves to grass roots. If you do not have actively growing grass, and thus a poor root system, these fungi will have little impact. When you previously did this early last summer, I suspect that it did not add much value to your soil since your turf had not yet established a strong root system. Often the nutrients added by this treatment are nitrogen and phosphorous. Soils in the metro area typically have very high phosphate levels. These same soils may or may not have high nitrogen. In short you may be gaining very little with a mycorrhizal treatment in a no-mow yard. Certainly it might not be worth your time, effort, and expense to do this until after a soil analysis is done. See:

https://graniteseed.com/product-category/planting-aids/mycorrhizal-inoculum/

https://aggie-horticulture.tamu.edu/faculty/davies/research/mycorrhizae.html

https://www2.nau.edu/~gaud/bio300/mycorrhizae.htm

4). My colleague’s comments about grass seeding are excellent. I can add nothing further to them.

Doing a soil test next spring is the single best thing you can do. In its absence you have very limited information upon which to plot your course of action.

Good Luck!!

Thanks for your response.

A core aeration early next spring before doing any over seeding or any fertilizing would be the next opportunity to do this. Your soil analysis was rather typical for Ramsey County with a high sand content (coarse texture) and low organic levels. After your aeration next spring (mid-April or so), ranking in some organic compost would be a good move. Then in early May, do a seeding of the no-mow fescue. Cooler temperatures at that time of the season would be perfect for the fescue. Water things well and frequently. Avoid applying any pre-emergent herbicide (or “weed and feed”) prior to your grass seeding as this will inhibit grass germination.

The recommended fertilizer from your soil test was 5-5-20 (i.e., 5% nitrogen, 5% phosphate, 20% potash. Turf fertilizers with this composition can be ordered online. You could also next spring call around to various gardening centers and big-box stores to see if they carry a fertilizer with this composition. If such is not locally available get a fertilizer that is the closest to these specifications. Note that your analysis indicates that the amounts of these nutrients are on an annual basis so this would be 0.5 pounds of nitrogen per 1,000 square feet in the spring and 0.5 pounds of nitrogen per 1,000 square feet in late summer or early September. Same would apply to the phosphate and potash recommended amounts; half the recommended amounts in the spring and half the recommended amounts in late summer. If you found a fertilizer having 5% nitrogen, then every pound of this fertilizer would contain 0.05 pounds of nitrogen. If you wanted to apply 0.5 pounds of nitrogen per 1,000 square feet next spring, you would then add 10 pounds of this fertilizer per 1,000 square feet next spring. Apply the fertilization about three weeks after the fescue seeding.

You may have difficulty in finding a lawn fertilizer containing phosphate as Minnesota law prohibits phosphate from being applied to a lawn unless a need is established through a soil test. If you apply a lawn fertilizer having only nitrogen and potash and no phosphate, this should still be fine.

If you utilize a lawn service, sometimes they are able to formulate a fertilizer per your specifications.

You may want to consider using a fertilizer having a 10-10-10 composition. This would be reasonably close to the suggested 5-5-20. A pound of this fertilizer would contain 0.1 pounds of nitrogen, 0.1 pounds of phosphate, and 0.1 pound of potash. To supply 0.5 pounds of nitrogen in spring 2022 per 1,000 square feet would require the application of 5 pounds of this fertilizer per 1,000 square feet.

Yet another possibility is to mix some muriate of potash with your other fertilizer. This product contains 60% (0.6) pounds of potash per pound of the muriate. If you applied 5 pounds of 10-10-10 next spring per 1,000 square feet, you would be adding 0.5 pounds of potash per 1,000 square feet. Your spring target for potash would be 2 pounds per 1,000 square feet. Mixing two pounds of muriate of potash with the 5 pounds of 10-10-10, would add an additional 1.2 pounds of potash which would bring you reasonably close to the target of 2 pounds potash per 1,000 square feet. See:

https://homeguides.sfgate.com/add-soluble-potash-lawn-73076.html

The following lawn care calendar may also be of interest to you:

https://extension.umn.edu/planting-and-growing-guides/lawn-care-calendar

Good Luck

Glad to have been of assistance!!