[CharlieO]

It depends on what type of fertilizer you are using. If you're using a "weed and feed" fertilizer, it's probably best to do it after it rains because the weed killer supposedly needs to sit on the weeds for a couple of days to do its job. It would stick to the weeds better if they're damp, I guess. I used to do it early in the day, when the dew was still on the lawn. If you're using standard fertilizer, you should do it before it rains, or water it in.

I used to do my first fertilizer application of the year very early when I lived in Wisconsin. Sometimes I'd do it in late February or March when the ground was still frozen. Of course, it wouldn't do anything until the ground thawed, but my lawn greened up earlier than my neighbors' did.