Should I cover sod with a tarp if I am not ready to install and it is raining?
No. You do not need to cover the sod with a tarp if it is raining. The water will not harm the sod in any way! The only drawback to keeping it uncovered is that the top layer of sod rolls will be a little wet and heavy when its time to install.
Covering sod pallets with a tarp is generally a bad idea*
The number one enemy of sod stacked on a pallet is heat. Heat leads to decomposition and dead sod! This is why you keep sod rolled up for up to 3 weeks in the winter and still have healthy grass, but in the summer you only have 24 hours to get it installed!
Covering sod with a tarp will trap heat in the pallet and speed the decomposition process. Also, tarps in direct sunlight will actually act as a greenhouse and get the sod really hot!
*The only time we recommend tarping sod pallets is if you are leaving sod overnight and the temperature is predicted to fall below freezing. This will insulate the sod and prevent the rolls from freezing overnight... No one likes trying to install frozen rolls of sod!