What Compost Tea Is and Why You'd Make It

Compost tea is water that has had finished compost steeped in it, the way you'd steep tea leaves. The result is a liquid rich in beneficial microorganisms and nutrients that you spray or pour onto soil and plants. You make it by submerging compost in water for a set time—usually 24 to 48 hours—then straining out the solids and using the liquid.

The main reason to make it is speed. Finished compost works slowly when you mix it into soil; compost tea delivers those microbes and nutrients to plant roots and leaves much faster. Gardeners use it to boost soil health before planting, to feed plants mid-season, or to spray directly on foliage as a foliar feed. It's also a way to stretch a smaller amount of finished compost across a larger garden.

You don't need special equipment or ingredients beyond what you likely have already. A bucket, some finished compost, water, and time are enough to start.

Key Takeaways

  • Compost tea is made by steeping finished compost in water for 24 to 48 hours, then straining and using the liquid on soil or plants.
  • A basic batch requires only a bucket, finished compost, dechlorinated water, and a way to strain—no aerator or special equipment needed.
  • If your tap water is chlorinated, let it sit uncovered for 24 hours before use, or use collected rainwater instead.
  • Use compost tea within a day or two of making it, because the microorganisms die off quickly once the brewing stops.
  • Spray or pour the tea onto soil around plants, or mist it directly on leaves in early morning or late evening to avoid leaf burn.

The Basic Method: Steep, Strain, and Use

Fill a bucket about three-quarters full with water. Add finished compost—roughly one part compost to four or five parts water by volume. A five-gallon bucket works well; use about one gallon of finished compost. Stir it once to distribute the compost evenly through the water.

Let it sit for 24 to 48 hours at room temperature. You don't need to stir it again or add air; passive steeping works fine for a basic batch. The water will darken and take on an earthy smell as the microbes and nutrients leach out.

After the time is up, strain the mixture through cheesecloth, an old t-shirt, or a fine mesh strainer into a clean bucket or watering can. Discard the solids (you can add them back to your compost pile). What remains is your compost tea, ready to use.

Water Quality Matters: Chlorine and Other Issues

Tap water in most cities contains chlorine to kill pathogens for human consumption. That same chlorine can harm the beneficial microorganisms you're trying to cultivate in your tea. If your water is chlorinated, let it sit in an open bucket for 24 hours before mixing it with compost. The chlorine will evaporate into the air.

Rainwater or well water sidesteps this problem entirely. If you collect rainwater in a barrel or tank, use that instead—it's free of chlorine and often preferred by gardeners for this reason. If you have well water and know it's not treated, you can use it straight away.

Water temperature doesn't matter much for a basic batch, but room temperature (around 65 to 75 degrees Fahrenheit) is fine. Cold water slows microbial activity slightly, but the tea will still work.

Using Your Compost Tea on Soil and Plants

Pour or spray the tea onto the soil around the base of plants, aiming for the root zone. A watering can with a rose attachment works well for this. You can also use a spray bottle or garden sprayer to mist it directly onto plant leaves—this is called a foliar process and works especially well for vegetables and herbs mid-season.

If you're spraying foliage, do it in early morning or late evening when temperatures are cooler and the sun is low. Spraying in hot sun can cause leaf burn. Drench the leaves until the tea drips off, coating both the top and underside of the foliage.

For soil process, use the tea as you would a liquid fertilizer. Pour it around the base of plants, keeping it a few inches away from the stem to avoid rot. One process per plant is usually enough, though you can repeat every two to four weeks during the growing season if you have plenty of tea.

How Long Compost Tea Stays Good

Use your compost tea within one or two days of making it. The beneficial microorganisms are most active right after brewing stops. After a few days, they begin to die off because the nutrients that fed them are depleted and oxygen becomes scarce in a sealed container.

If you need to store it briefly, keep it in a cool place out of direct sunlight. Don't seal the container tightly; microbes need some air. A loose cloth over the top of the bucket is fine. Beyond two days, the tea loses most of its benefit, so it's better to make smaller batches more often than to brew a large batch and let it sit.

When to Skip the Aerator and When to Add One

Many compost tea recipes call for an air pump and air stone to bubble oxygen through the mixture while it brews. This is called aerated compost tea, and it does increase microbial activity and speed up the process. However, it's not required for a working batch.

A basic, non-aerated batch made in a bucket for 24 to 48 hours will still contain plenty of beneficial microbes and nutrients. If you're new to making compost tea, start without an aerator. Once you're comfortable with the process and want to experiment, you can add an aquarium air pump and stone (both inexpensive) to speed things up and boost the microbial count.

The trade-off is simplicity versus potency. Non-aerated tea is easier and requires no equipment; aerated tea is stronger but takes a bit more setup.

Common Mistakes and How to Avoid Them

Using chlorinated water without letting it sit first is the most common mistake. The chlorine kills the microbes you're trying to grow, leaving you with nutrient-rich water but not much else. Always dechlorinate first, or use rainwater.

Waiting too long to use the tea is the second mistake. After three or four days, most of the benefit is gone. Make smaller batches and use them quickly rather than brewing a large batch and storing it.

Using immature or poor-quality compost is a third issue. If your starting compost is hot, moldy, or hasn't finished breaking down, the tea will reflect that. Always start with finished compost that smells earthy and crumbly, not sour or ammonia-like.

Oversaturating plants with tea is less common but possible. One process per plant per month is usually plenty. More won't hurt, but it won't help much either, and you'll use up your tea faster.

Frequently Asked Questions

Can I use fresh compost or kitchen scraps instead of finished compost?

Fresh or hot compost will make a tea, but it may smell bad and could introduce pathogens or weed seeds to your plants. Always use finished compost—the kind that's dark, crumbly, and smells like soil. If you're not sure your compost is finished, wait another month or two before brewing.

What if my compost tea smells like rotten eggs or ammonia?

That smell means anaerobic (oxygen-starved) bacteria have taken over, usually because the mixture was too dense or sat too long in a sealed container. Don't use it. For your next batch, use less compost relative to water, and don't seal the bucket tightly while it brews.

Can I make compost tea in a jar on a windowsill?

Yes. A quart or gallon jar works fine for small batches. Use the same ratio of compost to water, cover loosely with cloth, and brew for 24 to 48 hours. Strain and use the same way. A jar is actually a good way to start if you're making tea for just a few plants.

Will compost tea work on indoor houseplants?

Yes, but use it sparingly. Pour a small amount into the soil around the base of the plant, the way you'd water it. Don't spray it on foliage indoors—it can drip and stain surfaces. Once a month is plenty for indoor plants; they don't need as much feeding as outdoor plants.

Can I reuse the compost solids left in the strainer?

Absolutely. The solids still contain nutrients and structure. Add them back to your compost pile or mix them into garden beds. Nothing is wasted in this process.