In cold weather, you need to protect the bottom of your hammock from wind exposure. A good wind block in windy conditions is crucial to allowing your underquilt to work properly.
To provide windblock to the hammock bottom you have 2 options:
Add an underquilt protector, seasonally as needed. This is a great option, and it upgrades your 3 season tarp to full winter coverage.
Another option is to use a full size tarp such as our Superfly. Folks going this route often have another smaller tarp for warmer weather.