Easy Slow Cooker Lentil Soup
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This slow cooker lentil soup is thick, hearty and packed with red lentils, potatoes and vegetables in a flavourful herby broth. Everything goes straight into the slow cooker with no pre-cooking, making it an easy, inexpensive dinner for busy days.
If you love hearty lentil recipes, try my Turkish lentil soup or red lentil dhal next, or browse my soup recipes for more easy, warming meals.
Why this recipe works
Ingredients required
- Red lentils: These break down as they cook, naturally thickening the soup and giving it its hearty, creamy texture. There’s no need to cook them before adding them to the slow cooker.
- Onion, carrots and celery: The vegetable base of the soup. They add sweetness, savoury flavour and plenty of texture without needing to be sautéed first.
- Potatoes: Make the soup more substantial and add extra body as they soften. Cut them into roughly even cubes so they cook at the same rate.
- Dried oregano, basil and sage: A simple combination of herbs that gives the broth plenty of savoury flavour. Fresh thyme and bay leaves add another layer of earthiness as the soup slowly cooks.
- Worcestershire sauce: Adds a small but important hit of savoury, umami flavour that gives the vegetable and lentil broth more depth.
- Vegetable stock: Forms the base of the soup. Using stock rather than water seasons the lentils and vegetables as they cook.
- Kale: Added towards the end so it softens without completely disappearing into the soup. It also adds colour and texture to an otherwise very hearty, earthy soup.
- Vinegar or lemon juice: A small amount of acidity added at the end brightens all the slow-cooked flavours. Don’t skip this—the soup tastes noticeably more balanced once it’s added.
- For serving
- Fresh parsley, olive oil and Parmesan: Fresh parsley and a drizzle of olive oil add freshness and richness, while Parmesan brings a salty, savoury finish.
See the recipe card at the bottom of the post for exact quantities and full instructions.
Here’s How to Make Slow Cooker Lentil Soup
- Add the vegetables and lentils.
Add the red lentils, chopped potatoes, carrots, celery, onion, dried herbs, fresh thyme and bay leaves to the slow cooker. - Add the stock and seasonings.
Pour in the vegetable stock and Worcestershire sauce, then stir everything together. Cover and cook on medium for 3–4 hours or low for 6–8 hours, until the lentils are soft and the vegetables are tender.
- Add the kale.
In the last 15 minutes of cooking, stir in the chopped kale and leave it to wilt in the hot soup. Remove the bay leaves and thyme stems. - Blend and finish.
Scoop out about one-third of the soup and blend until smooth, then stir it back into the slow cooker. This thickens the broth while keeping plenty of the lentils and vegetables intact. Finish with the vinegar or lemon juice, then taste and adjust the seasoning before serving.
Chef’s Guide: Expert Tips
Here are a few simple tips, drawn from my training and kitchen experience, to help you get the best results every time.
- Rinse the lentils first. Rinse the red lentils under cold running water until the water is mostly clear. This removes excess surface starch and any dust before they go into the slow cooker.
- Cut the vegetables evenly. Keep the potatoes and carrots roughly the same size so they become tender at the same time. Avoid cutting them too small—they have several hours of cooking ahead of them.
- Blend only part of the soup. Blending about a third gives you a thick, creamy broth while keeping plenty of whole lentils and vegetables for texture. For a thinner soup, simply blend less.
- Adjust the consistency at the end. Lentils continue absorbing liquid as they sit, so don’t worry if the soup looks slightly looser when it first finishes cooking. If it’s too thick, stir in a little extra hot stock until it’s exactly how you like it.
- Add the acid last. Finish with the vinegar or lemon juice only after the lentils and vegetables are tender. The acidity lifts the earthy lentils and slow-cooked vegetables and makes the finished soup taste noticeably brighter.
What to do with leftovers
- Fridge: Let the soup cool completely, then store it in an airtight container in the fridge for up to 4 days.
- Freezer: This lentil soup freezes really well. Portion it into airtight containers and freeze for up to 3 months. Leave a little room at the top of each container for expansion.
- Reheating: Reheat gently in a saucepan over medium-low heat, stirring occasionally, until piping hot throughout. Individual portions can also be reheated in the microwave.
- Adjust the consistency: The lentils will continue to absorb liquid as the soup sits, so leftovers will usually be thicker. Add a splash of water or vegetable stock as you reheat until the soup reaches your preferred consistency.
FAQ’s
No. Red lentils don’t need soaking and can go straight into the slow cooker after a quick rinse. They’ll soften and begin to break down as the soup cooks, helping to thicken the broth.
I wouldn’t recommend a straight swap. Green and brown lentils hold their shape much more than red lentils, so they won’t give this soup the same naturally thick, creamy texture. They may also need a different cooking time.
Red lentils absorb a lot of liquid, and the soup will thicken further as it cools. Stir in a little hot vegetable stock or water until it reaches your preferred consistency. If you’re reheating leftovers, you may need to add another splash.
Absolutely. You can leave the soup chunky if you prefer. The red lentils will still soften and thicken the broth, but blending a portion gives it a creamier consistency while keeping some of the vegetables intact.
The Best Easy Slow Cooker Lentil Soup
Ingredients
- 1 large onion, diced
- 3 –4 celery stalks, chopped
- 3 carrots, peeled and chopped
- 2 large potatoes, cut into 2.5cm cubes
- 165 g (1 cup) red lentils, rinsed
- ½ tablespoon dried oregano
- ½ tablespoon dried basil
- 3 sprigs fresh thyme, leaves picked
- 1 tablespoon sage
- 1 tablespoon Worcestershire sauce
- 2 bay leaves
- 800 ml (3 ¼ cups) vegetable stock, made with a stock cube
- 50 g (2 ¼ cups) kale, roughly chopped
- 1 teaspoon vinegar or lemon juice
- For serving
- 2 tablespoons fresh parsley, chopped
- 1 tablespoon olive oil
- 10 g (⅓ oz) Parmesan cheese, grated
Instructions
- Add the vegetables and lentils. Add the onion, celery, carrots, potatoes, rinsed red lentils, oregano, basil, thyme, sage and bay leaves to the slow cooker.
- Add the stock and cook. Pour in the vegetable stock and Worcestershire sauce, then stir everything together. Cover and cook on medium for 3 hours, or until the lentils are soft and the vegetables are tender.
- Add the kale. Stir in the chopped kale for the final 15 minutes of cooking, allowing it to soften in the hot soup. Remove the bay leaves.
- Blend and finish. Transfer about one-third of the soup to a blender and blend until smooth. Stir it back into the slow cooker to thicken the broth while keeping plenty of vegetables intact. Add the vinegar or lemon juice, then taste and adjust the seasoning.
- Serve. Divide the soup between bowls and finish with the chopped parsley, a drizzle of olive oil and grated Parmesan.
Notes
- To make on the hob: Heat 2 tablespoons of oil in a large, heavy-based saucepan over medium heat. Add the onion and cook until softened, then add the remaining vegetables, lentils and herbs. Pour in the vegetable stock and Worcestershire sauce, bring to a gentle simmer and cook for approximately 45 minutes, or until the potatoes and lentils are tender.
- Add the kale towards the end, then blend a portion of the soup and finish as directed above.
- Adjusting the consistency: Red lentils continue to absorb liquid as the soup sits. If it becomes too thick, stir in a little hot vegetable stock or water until it reaches your preferred consistency.
- Fridge: Cool the soup promptly and refrigerate in an airtight container for up to 3 days.
- Freezer: Freeze in airtight containers for up to 3 months. Defrost overnight in the fridge before reheating.
- Reheating: Reheat in a saucepan or microwave until piping hot throughout, adding a splash of stock or water if needed.
Nutrition
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Meet the Chef!
Hi, I’m Debs, a Cordon Bleu-trained chef dedicated to helping you create unforgettable meals on a budget. Discover more about my journey and dive into a world of foolproof recipes designed for those who love to eat well without overspending.
Really lovely. My favourite soup.
Delicious soup! Very easy and quick to make. I added peas instead of kale (question of personal preference). Really warming on a cold January lunchtime!
I bet this was so great with the peas! The perfect warming soup for cold winters! 🙂
The amount of kale to be used is not listed anywhere in the recipe! This error must be corrected before anyone can try it!
Thanks for catching that! The recipe has been updated. A couple of handfuls is the perfect amount. The recipe has been updated now.