Key takeaways
- Jar sprouts need no soil and no light until the final day
- Rinse and drain twice a day, three times in warm weather
- Lentils take about 2 to 4 days, mung beans 4 to 6 and alfalfa about 5
- Use seed sold for sprouting or eating, never garden seed
- Fine white root hairs are normal, but grey fuzz, slime or a sour smell mean bin it
- Vulnerable people should cook sprouts until steaming hot
Jar sprouting is the easiest food you’ll ever grow. You need a glass jar, some seed and cold water, and in a few days you’ll have fresh, crunchy sprouts. There’s no soil and no light needed until the last day. The one thing you mustn’t skip is the rinsing.
This guide covers the jar method for alfalfa, mung beans and lentils, step by step. Sprouts are eaten whole, seed, root and all. That’s different from microgreens, which are grown in compost and snipped. For those, see our guide to windowsill sprouts and microgreens.
How does jar sprouting work?
The seed grows on its own stored energy. Add water and warmth, and it pushes out a root and a shoot. You eat it before it ever needs feeding, so there’s no compost or light involved.
You’ll need:
- A clean glass jar. A 1-litre jar suits one or two tablespoons of seed.
- A lid that lets water through, such as muslin held with an elastic band, or a mesh sprouting lid.
- Somewhere to tilt the jar so it drains, such as a dish rack or a bowl.
The routine is soak, rinse, drain, repeat. Soak the seed once to wake it up. Then rinse and drain twice a day so the seed stays damp but never sits in water. Standing water is the enemy. It drowns the seed and lets bacteria grow.
Which seeds to sprout and how long they take
Lentils, mung beans and alfalfa are the easiest three. This table shows how long each one needs.
| Seed | Soak | Ready in | Light on last day? | Best eaten |
|---|---|---|---|---|
| Whole lentils | About 8 hours | 2-4 days | No | Raw in salads, or cooked |
| Mung beans | About 12 hours | 4-6 days | No, keep dark | Stir-fries, salads |
| Alfalfa | About 8 hours | About 5 days | Yes, a few hours | Sandwiches, salads |
| Radish | About 8 hours | 3-5 days | Yes, a few hours | Salads, for a peppery kick |
Whole lentils from the food aisle sprout brilliantly. Split lentils won’t sprout, because the seed has been cut in half. Mung beans give the fat beansprouts you get in a takeaway. Alfalfa and radish are tiny seeds that turn into a fine tangle of leafy sprouts.
Warning: Don’t eat sprouted kidney beans raw. Raw kidney beans contain a toxin that only hard boiling destroys. Cook chickpeas and larger beans after sprouting too.
Alfalfa sprouts are ready in about five days. A few hours of daylight at the end turns the little leaves greener.
The day-by-day sprouting routine
The routine is the same for every seed. Only the timings change. Here’s how a jar of alfalfa goes.
| Day | What to do | What you’ll see |
|---|---|---|
| Day 0, evening | Rinse a tablespoon of seed, cover with cold water and soak overnight | Seed swells |
| Day 1 | Drain, rinse, drain well and tilt the jar | Seed coats split, tiny roots appear |
| Day 2 | Rinse and drain morning and evening | Short white roots |
| Day 3 | Rinse and drain morning and evening | Stems lengthen. Fine root hairs may appear |
| Day 4 | Rinse and drain. Move into indirect light | Pale leaves start to open |
| Day 5 | Final rinse, drain very well, refrigerate | Green leaves, ready to eat |
After every rinse, rest the jar mouth down at an angle so the last drops run out. A dish rack is perfect. A jar left upright keeps a puddle in the bottom, and that’s where batches go wrong.
Keep the jar somewhere cool and out of direct sun. If your kitchen gets hot in summer, add a third rinse and try a cooler room.
Fill the jar through the mesh lid, swirl, then tip all the water out. A good drain after every rinse keeps sprouts fresh.
Growing mung beans and lentils
Mung beans take the longest of the common seeds. Soak them for about 12 hours, then rinse twice a day for four to six days. For thick, crisp beansprouts, keep them in the dark. Some people rest a small clean weight, such as a saucer, on top so the stems grow sturdier.
Lentils are the quickest. After an overnight soak, they show a curly white root by day two and are ready at day three or four. Eat them young, before the roots get stringy.
Neither needs any light. A cupboard works just as well as a windowsill. Our guide to growing sprouts and shoots covers mung beans alongside pea and sunflower shoots.
Mung beans grown in the dark stay pale, sweet and crunchy. They’re ready in four to six days.
Are sprouts safe to grow at home?
Yes, with clean seed and good habits. But the warm, damp jar that suits the seed also suits bacteria, so take food safety seriously.
- Use seed sold for sprouting or eating. Never use garden seed, which may be treated.
- Rinse twice a day with cold water, three times in warm weather.
- Keep the jar cool and draining, never sitting in water.
- Refrigerate the sprouts as soon as they’re ready, and eat them within a few days.
- Smell every batch. Fresh sprouts smell clean and green. A sour or musty smell means bin the lot.
Warning: Raw sprouts have been linked to food poisoning outbreaks. Pregnant women, young children, older people and anyone with a weakened immune system should cook sprouts until steaming hot before eating.
Lentils are the fastest sprouts of all. Eat them when the root is short, before it turns stringy.
Root hairs or mould? How to tell
Around day three, fine white fuzz often appears around the roots. Usually it’s root hairs, which are a normal, harmless part of growing.
Fine white fuzz spread evenly round each root is just root hairs. Mould is grey or green, patchy and smells musty.
Root hairs are pure white, soft, grow evenly all round each root, and flatten or vanish when you rinse.
Mould is grey, blue-grey or green. It sits in patches, often on the seed coats, smells musty and stays put after rinsing.
Not sure? Rinse the jar and look again in an hour. Gone means root hairs. Still there and smelly means mould. Slime is the other warning sign. Healthy sprouts feel firm and squeaky. If they’re slimy or the rinse water is cloudy, throw the batch away, scald the jar and start again.
Common sprouting mistakes
Most failed jars come down to one of these.
- Leaving the jar upright. Water pools at the bottom. Always tilt it mouth down.
- Skipping rinses. Two a day is the minimum, three when it’s warm.
- Too much seed. Sprouts swell a lot. A tablespoon or two is plenty for a 1-litre jar.
- A hot spot. Direct sun or a warm kitchen speeds up spoiling. Keep jars cool.
- Using split lentils or garden seed. Split lentils won’t sprout, and garden seed isn’t for eating.
Storing and eating your sprouts
Give the finished sprouts a final rinse, then drain them as dry as you can. Wet sprouts rot in the fridge. Spin them in a salad spinner or roll them gently in a clean tea towel.
Store them in a tub lined with kitchen paper in the fridge and eat them within a few days. Pile alfalfa and radish sprouts onto sandwiches and salads. Toss mung beansprouts into a stir-fry in the last minute so they keep their crunch.
For a steady supply, start a new jar every couple of days so you always have one ready.
Start a new jar every couple of days and you’ll have fresh sprouts ready all week.
If you’ve caught the indoor growing bug, try cress and watercress, or see our guide to winter vegetables to grow indoors. The windowsill mini-garden ideas for kids make a great family project too. Find more ideas in our growing hub.
Frequently asked questions
Are home-grown sprouts safe to eat?
Yes, for most people, if you use clean sprouting seed and rinse twice daily. Raw sprouts have been linked to food poisoning, so pregnant women, young children, older people and anyone with weak immunity should cook them until steaming hot.
How long do mung bean sprouts take to grow?
About four to six days after an overnight soak. Short sprouts are ready at day four, and longer beansprouts at day five or six. Grow them in the dark for pale, crisp stems.
Do sprouts need sunlight to grow?
No, sprouts grow happily in the dark. The seed feeds the sprout. Give leafy sprouts like alfalfa a few hours of indirect light on the last day to green up. Keep jars out of direct sun.
What is the white fuzz on my sprouts?
It’s usually harmless root hairs, not mould. Root hairs are fine, white, even all round the root and vanish when you rinse. Mould is grey or green, patchy and smells musty.
Can I sprout seeds from a garden centre packet?
No, use seed sold for sprouting or eating. Garden seed may be treated and isn’t meant to be eaten. Whole lentils and mung beans from the food aisle work well.
Which beans should I not sprout and eat raw?
Don’t eat sprouted kidney beans raw. Raw kidney beans contain a toxin that only hard boiling destroys. Larger beans and chickpeas are best cooked after sprouting.
Ready for the next step? Read our guide to growing microgreens and grow tiny leafy crops in trays of compost.
Our team produces practical UK gardening guidance from source research, contributor records and established horticultural practice. Editorial standards are overseen by Matt W.
