Add the diced carrots, parsnips, butternut squash, chopped onion, and minced garlic into the slow cooker. Spread them out evenly to create a colorful base.
Pour in the vegetable broth over the vegetables, ensuring they are mostly submerged. Sprinkle the dried thyme and sage evenly over the top.
Season with salt and pepper according to your taste. Cover the slow cooker with its lid before setting it to cook on low for about 6 hours, or until the vegetables are tender and fragrant.
Once the cooking time is up, carefully open the lid and use an immersion blender directly in the slow cooker to blend the soup until smooth and creamy. Alternatively, transfer the hot mixture to a blender in batches and puree until silky.
Check the consistency and season with additional salt, pepper, or herbs if needed. The soup should be thick, with a warm, inviting aroma and a smooth, velvety texture.
Spoon the hearty, earthy-colored soup into bowls. Serve hot, garnished with a sprinkle of fresh herbs or a drizzle of olive oil if desired. Enjoy this comforting seasonal dish!