Compost Leachate: What It Is and What to Do With It

After a few days with your compost bin, a dark liquid shows up at the bottom of the bucket. Many people get worried and think something went wrong. In fact, it’s leachate, and it’s a normal part of composting.

Compost leachate is the liquid that drains from fruit and vegetable scraps as they break down. It’s normal and, when handled well, it becomes a liquid fertilizer for your plants. What matters is draining it often, never using it undiluted and paying attention to its smell, because it shows whether your compost bin is balanced.

In this guide, you’ll learn why leachate forms, how to tell if it’s healthy and what to do when there’s too much of it, when it smells bad or when none comes out at all.

What is compost leachate?

Compost leachate is the water that was inside your food scraps and gets released during decomposition. As it drains through the mix, this water carries some of the nutrients from the material that’s turning into compost. That’s why it’s dark and can be used on plants, as long as it’s diluted in water.

Despite the name, it’s very different from landfill leachate. That kind comes from mixed garbage, with plastic, chemicals and all sorts of waste. Home compost leachate comes only from plant scraps and, if everything is balanced, doesn’t smell like garbage.

In worm bins, this liquid is also often called “worm tea.” It’s the same liquid that drains into the collection bucket or comes out of the spigot.

Why does a compost bin produce leachate?

A compost bin produces leachate because fruits and vegetables contain a lot of water. When microorganisms and worms break down these scraps, the water is released and drains to the bottom. The more wet scraps you add, like watermelon rinds, orange peels and lettuce leaves, the more leachate your compost bin produces.

That’s why the amount of leachate varies from home to home and from week to week. It depends on what you eat, the time of year and how much dry material goes in with the scraps.

How can you tell if compost leachate is healthy?

Healthy leachate is dark brown, like strong tea, and smells like damp soil or slightly sweet, like fermentation. If it smells rotten, like spoiled eggs or very sour, it’s a sign that your compost bin is too wet and isn’t getting enough air.

What you notice	What it means	What to do
Dark brown liquid that smells like soil	A balanced compost bin	Keep up your routine and drain the leachate often
Sour or rotten smell	Too much moisture and not enough air	Add dry material, stir the mix and empty the collector
Lots of liquid in just a few days	Scraps that are too wet and too little dry material	Balance it with sawdust, dry leaves or shredded cardboard
No liquid for a long time	A dry mix or a clogged drain	Check the holes and the spigot and, if needed, add more fresh scraps
Foam, mold or tiny bugs in the collector	Liquid that has been sitting for too long	Empty and wash the collector, and drain the leachate more often

What should you do when compost leachate smells bad?

When leachate smells bad, your compost bin needs air and dry material. Empty the collector, add a good layer of sawdust, dry leaves or shredded cardboard, stir the mix well and check that the ventilation holes are clear. If you added meat, dairy or seasoned food, take those scraps out.

The bad smell happens because, without oxygen, other microorganisms take over, and they break things down more slowly and with a stronger odor. Once air is flowing again, the smell usually improves.

A detail many people miss: leachate that sits in the collector for too long also starts to smell bad, even when the compost bin itself is fine. That’s why draining the liquid regularly is just as important as caring for the mix. Our article on how to speed up composting without bad smells has more tips to keep everything in order.

What should you do when there’s too much leachate?

Too much leachate means too many wet scraps and too little dry material are going in. To balance it, cover each batch of scraps with dry material, chop and drain watery foods before adding them, and empty the collector more often. That way, the mix stops getting soggy.

A few practical tips:

Drain scraps first. Peels that were soaking or leftover washed salad should lose their excess water.
Go easy on very watery scraps. Watermelon, cantaloupe and orange peels release a lot of liquid. Add them in smaller portions and always with plenty of dry material.
Add more browns. Sawdust, plain cardboard and dry leaves absorb moisture and balance the mix.
Don’t let the collector fill up. If the liquid reaches the bottom of the bucket above it, the mix gets soggy and worms can drown.

Why isn’t my compost bin producing any leachate?

Your compost bin may not produce leachate because the mix is dry, because it gets few wet scraps or because the holes and spigot are clogged. In small compost bins with plenty of dry material, it’s normal for little liquid to come out. That’s not a problem, as long as the mix stays as damp as a wrung-out sponge.

To find the cause:

Squeeze a handful of the mix. If it crumbles and has no moisture at all, it’s too dry. Add more fresh scraps or spray on a little water.
Check the bottom holes. In a bucket compost bin, scraps and compost can block the holes that carry liquid to the collector.
Clean the spigot. Small bits of food often clog the outlet. Take it apart, wash it and, if possible, place a fine mesh over the opening.

If you haven’t built yours yet, our step-by-step guide to a stacked bucket compost bin shows how to drill the holes and leave room for the collector.

How do you drain and store compost leachate?

Drain the leachate through the spigot or by emptying the collection bucket whenever liquid builds up. Store it in a tightly closed bottle, preferably a dark one, in a cool place away from sunlight, and write down the date. It’s best to use it soon, because leachate stored for too long can ferment and lose quality.

A few important precautions:

Label the bottle clearly, so no one mistakes it for a drink.
Keep it out of reach of children and pets.
Wear gloves or wash your hands well after handling leachate.
Don’t fill the bottle to the top. If the liquid ferments, it can release gas.

How do you use compost leachate on plants?

Compost leachate should always be diluted in water before it goes on your plants. Undiluted, it’s too strong and can burn the roots. Once diluted, use it to water the soil in your pots, garden beds and planters. For vegetables that will be eaten raw, water the soil instead of wetting the leaves.

How much to dilute, how often to apply and how to use it in each type of container are explained in detail in our guide on how to use compost in pots, vertical gardens and hanging planters.

What can you do with leftover leachate?

If you produce more leachate than you can use, offer it to neighbors who have plants, use it in your building’s garden with permission or pour a little back into your compost bin when the mix is dry. As a last resort, dilute it well in water before pouring it down the drain.

Having lots of leftover leachate all the time is also a warning sign: your compost bin may be getting too many wet scraps. It’s worth reviewing the balance between wet and dry material, as shown in our list of what can and can’t go in your compost bin.

Summary: how to manage compost leachate

Remember that leachate is normal and part of composting.
Watch the color and smell: dark brown with an earthy smell means balance.
Drain the liquid often so the collector doesn’t fill up.
Balance with dry material when there’s too much leachate or a bad smell.
Unclog the holes and spigot if the liquid stops coming out.
Store it in a closed, labeled bottle and use it soon.
Never use it undiluted: always mix it with water before watering.

Leachate is a thermometer for your compost bin. Once you learn to read its signs, caring for your compost gets much easier. For all the other care tips, check out our complete guide to apartment composting. And if bugs are your current problem, our guide to fruit flies in the compost bin will help you solve it.

FAQ: compost leachate

Is compost leachate dangerous?

Leachate from a home compost bin, made only from plant scraps, isn’t dangerous when handled with care. Even so, it should never be drunk or used undiluted on plants. Store it in a labeled bottle, away from children and pets, and wash your hands after using it.

Does compost leachate smell?

It has a light smell, like damp soil or slightly sweet. A rotten, spoiled-egg or very sour smell isn’t normal. It means the compost bin is too wet and lacks air, or that the liquid has been sitting in the collector for too long.

Can I pour leachate back into the compost bin?

Yes, in small amounts and only when the mix is dry. It returns moisture and microorganisms to the compost. If your compost bin is already damp, don’t do it, because it can get soggy and start to smell.

How often should I drain the leachate?

Whenever liquid builds up in the collector. Ideally, check every time you feed your compost bin. That way, the leachate doesn’t sit, ferment or reach the mix above.

Are leachate and compost the same thing?

No. Compost (or humus) is the solid part, a dark, crumbly soil that forms at the end of composting. Leachate is the liquid part that drains during the process. Both can be used as fertilizer, each in its own way.

Does a compost bin without worms also produce leachate?

Yes, it does. Leachate comes from the water in food scraps, not from worms. That’s why it shows up both in worm bins and in compost bins that run only on microorganisms.