Answer: Lawns naturally look their worst at this time of year. The first thing to do is run some soil tests and determine the fertility level of the soil as well as the pH. This will tell you how to fertilize and whether or not you need to add lime to adjust the pH for growing healthy turf grass.
The best time of year for major lawn work is in late summer to early fall, but you should begin working on the soil conditions now in preparation for that. You may need to topdress with compost, do core aeration to loosen the soil and allow air and rain to penetrate it better, and you may want to spot treat for certain perennial weeds, for example.
In the meantime you may want to overseed to try to make it look as attractive as possible for now.
Mowing is also critical. Mow often enough that you never remove more than one third of the grass height at a time. This can mean mowing more than once a week in the spring. Correct mowing can help the existing grass grow denser.
I would suggest you work with your state extension service to interpret the tests and develop a lawn renovation and maintenance plan. Their web site offers detailed advice, information about soil testing, and they also have a help line. Here is the web site for the home and garden information
Good luck with your lawn!
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