To freeze turnips, first wash and trim the vegetables to separate the root from the greens. Cut the roots into 1/2-inch cubes, and add them to a large pot of boiling water for 2 minutes before transferring them to an ice bath to halt the cooking process.
Both the root and the greens can be blanched and frozen. Letting the vegetables cook for 2 minutes kills bacteria. Additionally, blanching doesn't fully cook the turnips, but it does halt the enzymatic action that causes the vegetables to decay. This is an essential step to maintain optimal flavor and texture while the turnips are frozen.
Once the blanched vegetables are completely cool, which typically takes 2 to 3 minutes, transfer them to a towel and dry the vegetables completely. Arrange the dry vegetables in a single layer on a baking sheet, and place the sheet in the freezer until the turnips are frozen. Once they are frozen, transfer the turnips to an airtight container or a resealable freezer bag to store in the freezer. Use a vacuum-seal the bags to remove as much air as possible and to get the best results. Turnip greens can be frozen for up to eight months, while the roots can generally be frozen for nine months in a regular freezer or 14 months in a deep freeze.