Fill clean sink about halfway with lukewarm water. Chop turnip greens and place into the sink to clean. Agitate the water and turnip greens with your hands to dislodge any dirt and grit from the turnip greens. Drain water and repeat once or twice until the greens feel clean and no dirt remains in the bottom of the sink when rinsing.
Spray insert of slow cooker with non-stick cooking spray.
Add half of greens to the slow cooker with about 1 cup of water, peeled and quartered turnips, and ham hock or olive oil. If you are using the sugar and red pepper flakes, add those as well.
Cook on low setting for about 1 hour until greens have reduced. Add remaining greens to the slow cooker and set time on low for 4 more hours.
Note: The longer turnip greens cook, the better the flavor, in my opinion.