Thanks for the question.

I am slightly confused. You indicated you overseeded about five weeks ago. You further stated that you added fertilizer at that same time. You then said that you will soon be adding fertilizer and aerating. You wanted to know when you should now overseed relative to aeration. Does this mean that you are considering a second overseeing?  Also if you have previously added fertilizer, are you now thinking of a second application of fertilizer?  Please clarify. 

Many thanks

Thanks for the question.

Have you recently done a soil test? In the absence of doing so, my comments regarding fertilizer recommendations may or may not be accurate. Think about doing this next spring (2022):

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

With this thought in mind, here are my comments and suggestions:

1). The Summer Guard you applied in August consisted of a large dose of fast release nitrogen. If you looked at the label on the fertilizer bag it probably indicated 32% nitrogen or something close to this. This may or may not have been a wise action since your yard was most likely in a state of dormancy at that time and would not have taken up much of the nitrogen. In other words, I suspect that your yard now has a rather high nitrogen content. You need to keep this in mind as you consider additional fertilization in order to avoid the possibility of “nitrogen burning” of your turf.

2). Applying the weed and feed now (mid-September 2021) is a great time to deal with the weeds. However the fertilizer component will further add to the soil’s nitrogen content and this may not be necessary. Instead I would suggest that you just apply a broad leaf herbicide (spraying) and not any fertilizer.

3). Aeration a week or so (late September, early October) after applying the herbicide would be a perfect time.

4). It wouldn’t hurt to overseed a second time. Play this by ear. Have you seen much germination from your August overseeding? Perhaps not? The August heat would certainly have impeded such germination. If there is scant growth, then overseed again. Wait to do this until after your aeration but don’t delay it much past the first few days of October.

5). Applying Winter Guard after aeration and possibly a second overseeding could be done. There is one major difference between the Winter Guard and the Summer Guard you previously applied. The nitrogen in Winter Guard is slow releasing which is exactly what you want for the winter months. Winter Guard will not make a significant contribution to available nitrogen in your soil this fall but this is OK since you took care of this in August. Winter Guard will slowly release nitrogen into the soil so that green-up in spring 2022 will be stimulated.

6). If you do overseed just after aeration, apply the Winter Guard about two weeks later (mid-October). There is stored energy in the grass seed to sustain initial germination and early growth so external fertilizer is not really needed at the time of seeding. Furthermore, application of fertilizer at the time of seeding can impede the germination process.

Please get back to us with any additional questions/comments you may have.

Thanks for using our forum.

Thanks for the response.

It is our policy as Master Gardeners at this forum not to make recommendations regarding specific brands or vendors. Look for a broad leaf herbicide containing one or more of the following 2,4-D, MCPP, and/or dicamba.

You are absolutely correct that any herbicide in the Winter Guard would interfere with grass germination. So pick a Winter Guard that is only fertilizer and does not contain any herbicide.

The Winter Guard may have more than 20% nitrogen. Its label will probably say something about slow release.

Again, we are here to address any additional questions you might have.