Depending on where you live, the answer to the question of whether or not it’s too late to fertilize your lawn in December can differ greatly. December is typically associated with a white Christmas, freezing temperatures and the fall of snow. But that isn’t the case everywhere, as there are places in southern Texas and New Mexico where people have never even seen snow in their entire lives.
The main issue is one of soil temperature. Fertilizing your soil using the best lawn fertilizer requires the soil to still be somewhat soft and receptive to the nutrients cast out by a slow release fertilizer. This means the temperature can’t be below freezing, so the task is typically handled sometime in early November in most places in the north.
If you live in a warmer area, however, December can be a great time to fertilize your lawn. Since soil temperatures here rarely – if ever – fall below freezing, but in some cases they can still be quite low in late November and early December, that time can be used quite effectively to fertilize your lawn for the last time before the coming of spring. As you use winter fertilizer, make sure you also aerate your soil to allow it to take in more nutrients, and cover it to prevent cold winds from negatively affecting your lawn throughout the season.