Use a 6-quart slow cooker.
Peel the carrots, rutabagas, and parsnip, and cut into about 2-inch chunks.
Put all the vegetables into your crockpot, and add the olive oil, basil, salt, and pepper.
Toss with your hands to fully coat the vegetables.
Cover and cook on low for 8 hours, or on high for 4-5 hours.
The vegetables are done when they have reached desired tenderness.