From the middle of December through the majority of winter, these are some of the best times to apply soil amendments to the lawn mostly because it isn’t growing and everything stays damp for so long if not frozen.
There are lots of things you can do to a lawn but I suggest focusing the early parts of winter on adjusting your soil pH higher or lowers depending on your own situation.
For soil testing I’ve used the following three mail-in kits and had no complaints with any of them. I suggest using whichever one is cheaper at the time you are reading this.
► Yard Mastery Kit
► My Soil Kit
► AgriTech Soil Kit
Below you’ll find uploads to the Turf Mechanic YouTube channel all about the process of applying Soil Sulfur to lower pH and Lime to raise pH. I’ve done both multiple times with great success.