I firmly agree. Another somewhat of a guide, is when about the first inch or two of topsoil reaches 50 degrees for two or more days consistently, then the product should be applied and ready. The only problem with this theory, is that beds have many other things in them - such as trees, ornamentals, and other stuff. These things collect heat and also deflect heat off of them and onto the ground. Also, consider beds around structures. These beds will be much warmer, faster than other areas - especially on south sides. But as SeedPro mentioned, be prepared and have your beds worked or whatever you're going to do AHEAD of time. Otherwise, if you stir the beds after, all bets are off...it will just be a waste.