Making Compost Tea Using Coffee Grounds

Quick Answer

• Coffee grounds are a fantastic addition to compost tea.
• They add nitrogen and beneficial microbes.
• The process is pretty simple, really.
• You’ll need coffee grounds, compost, water, and an aerator.
• Brewing time is typically 24-48 hours.
• Apply it to your plants for a healthy boost.

Who This Is For

• Gardeners looking for natural ways to feed their plants.
• Anyone with a steady supply of used coffee grounds.
• Folks who want to give their soil a little extra love.

What to Check First

Brewer Type and Filter Type

This isn’t about making coffee, but the principle is the same. You’re brewing nutrients. So, you need a way to hold your solids while letting the liquid out. A bucket with a lid and some sort of mesh bag or cheesecloth works fine. Or a dedicated compost tea brewer. Just make sure your filter is fine enough to keep the solids contained but open enough for aeration.

When you’re looking for a way to hold your compost solids while letting the liquid out, a fine-mesh bag is a great option. It ensures your nutrients are contained but aeration is still possible.

Sandbaggy Mesh Onion Produce Bags | Large 18" x 30 Inch Bags | 50 lb Capacity | Breathable Fabric | Great for Packaging Produce & Fruit (Pack of 25)

• LARGE 18" X 30 INCH MESH BAG - Made of industrial grade polypropylene with reinforced seams for a stronger bag
• 50 LB WEIGHT CAPACITY - Can hold up to 50 lbs. Strong enough to hang fruits, vegetables, & nuts or even store firewood without breaking!
• GREAT FOR FRUITS & VEGETABLES - Use to package or store onions, potatoes, apples, peppers, potatoes, corn, & more!
• BREATHABLE & SEE-THROUGH FABRIC - Allows product inside to be easily visible from the outside & allows produce to release excess moisture to extend shelf life
• ALSO GREAT FOR STORING FIREWOOD: The perfect size bags to hold firewood without breaking.

Buy on Amazon

Water Quality and Temperature

Tap water is usually okay for compost tea, but if yours is heavily chlorinated, let it sit out for 24 hours to let the chlorine dissipate. Chlorine can harm the beneficial microbes you’re trying to cultivate. Aim for room temperature water, around 65-75°F. Too cold and the microbes won’t be very active. Too hot and you might kill them.

Grind Size and Coffee Freshness

For compost tea, the grind size of your coffee grounds doesn’t matter as much as for brewing coffee. Whether it’s fine or coarse, it’ll break down. Freshness isn’t a huge concern either. Used grounds are what you want. They’ve already given up most of their caffeine.

Coffee-to-Water Ratio

A good starting point is about 1-2 cups of used coffee grounds per gallon of water. This gives you a decent nitrogen boost. Don’t go overboard; too much can lead to an imbalance. You can always adjust this next time based on how your plants respond.

Cleanliness/Descale Status

Make sure your brewing container and any equipment are clean. You don’t want to introduce unwanted bacteria or mold. If you’re using a repurposed bucket, give it a good scrub. The goal is to foster beneficial life, not a science experiment gone wrong.

Step-by-Step: How to Make Compost Tea with Coffee Grounds

1. Gather your materials. You’ll need a clean bucket (around 5 gallons is good), used coffee grounds, some finished compost, non-chlorinated water, and an aquarium pump with an airstone for aeration.

• What “good” looks like: Everything is ready to go, clean, and within reach. No scrambling mid-brew.
• Common mistake: Forgetting a key ingredient. Double-check your list before you start.

2. Add water to the bucket. Fill your bucket about 3/4 full with water. Letting it sit out overnight is ideal if you have chlorinated tap water.

• What “good” looks like: Clear, de-chlorinated water ready for the good stuff.
• Common mistake: Using straight, heavily chlorinated tap water. This can kill your beneficial microbes.

3. Add finished compost. Toss in about 1-2 cups of good quality finished compost per gallon of water. This is where the real microbial magic comes from.

• What “good” looks like: Nice, earthy-smelling compost going into the water.
• Common mistake: Using immature compost or just plain soil. You want mature, biologically active compost.

4. Add your coffee grounds. Now, add your used coffee grounds. Aim for 1-2 cups per gallon of water.

• What “good” looks like: Dark, moist grounds mingling with the water and compost.
• Common mistake: Adding too many grounds. This can throw off the nitrogen balance and make the tea smell funky.

5. Aerate the mixture. Place the airstone in the bottom of the bucket and turn on your aquarium pump. You want a vigorous bubbling action.

• What “good” looks like: A constant stream of bubbles rising from the airstone, creating turbulence.
• Common mistake: Not aerating enough. This leads to anaerobic conditions, which are bad news for your microbes.

6. Brew for 24-48 hours. Let the mixture bubble away. Stir it occasionally if you can, but the aeration does most of the work.

• What “good” looks like: The mixture should start to develop a slightly frothy, earthy-smelling brew. It shouldn’t smell rotten.
• Common mistake: Brewing for too short or too long. Too short, and you won’t get full extraction. Too long, and the microbes can start to run out of food.

7. Strain the tea. After brewing, turn off the pump. Strain the liquid through a fine-mesh sieve or cheesecloth to remove the solids.

• What “good” looks like: A dark, liquid nutrient solution with no large solids left behind.
• Common mistake: Not straining well enough. Large solids can clog sprayers if you’re using one.

8. Dilute the tea. Most of the time, you’ll want to dilute the compost tea. A common ratio is 1:10 (tea to water). So, 1 gallon of tea to 10 gallons of water.

• What “good” looks like: A lighter colored liquid that’s ready for application.
• Common mistake: Applying undiluted tea. This can be too strong for some plants.

9. Apply to your plants. Use the diluted tea to water your plants at the base or apply it as a foliar spray. Do this in the morning or evening.

• What “good” looks like: Plants getting a healthy drink of nutrients.
• Common mistake: Applying in direct sun. This can scorch leaves, especially if the tea is a bit concentrated.

10. Clean your equipment. Rinse out your bucket and airstone thoroughly. This prevents buildup and keeps your next batch clean.

• What “good” looks like: Clean gear ready for the next brewing cycle.
• Common mistake: Leaving the equipment dirty. This can lead to mold and funky smells.

Common Mistakes (and What Happens If You Ignore Them)

Decision Rules

• If your tap water smells strongly of chlorine, then let it sit out for 24 hours before brewing because chlorine can harm beneficial microbes.
• If your compost tea smells foul or rotten after brewing, then you likely didn’t aerate enough or brewed for too long because anaerobic conditions create bad smells.
• If you plan to use a sprayer, then strain your compost tea very well because large solids will clog the nozzle.
• If your plants are looking a bit yellow and weak, then applying compost tea can give them a good boost of nitrogen and micronutrients because that’s what it’s designed for.
• If you’re brewing for the first time, then start with a 1:10 dilution ratio because it’s a safe bet for most plants.
• If your coffee grounds are old and have visible mold, then discard them and use fresh used grounds because mold can be harmful to your plants.
• If you want to maximize microbial activity, then brew your tea between 65-75°F because this is the optimal temperature range.
• If you notice algae growing in your brew bucket, then it’s probably not a big deal, but it means you might need to clean your equipment more thoroughly next time because it indicates some aerobic conditions were present.
• If you only have a small garden, then a 5-gallon bucket is usually plenty for a batch of compost tea because you can always brew more if needed.
• If your plants are very young seedlings, then use a weaker dilution or apply less frequently because they are more sensitive to nutrient strength.

FAQ

Can I use fresh coffee grounds instead of used ones?

It’s best to use used coffee grounds. Fresh grounds can be too acidic and contain too much caffeine, which isn’t ideal for the microbes or your plants.

How often should I use compost tea?

Generally, you can apply compost tea every 2-4 weeks during the growing season. Watch your plants; they’ll tell you if they need more or less.

Does the type of compost matter?

Yes, use good quality, finished compost. Worm castings or well-rotted manure are excellent sources of microbes for your tea.

What if my tea looks cloudy?

A bit of cloudiness is normal, especially if it’s rich in microbes. It should still smell earthy, not rotten.

Can I add other things to my compost tea?

Some people add things like molasses or kelp meal for extra nutrients. Start simple first, then experiment.

How long does compost tea last once brewed?

It’s best to use compost tea within 24 hours of brewing and diluting. The beneficial microbes are most active then.

Will this tea attract pests?

When diluted and applied correctly, compost tea usually doesn’t attract pests. In fact, a healthy plant is less susceptible to pest issues.

Can I use compost tea on all my plants?

Compost tea is generally safe for most plants, including vegetables, fruits, flowers, and lawns. Just remember to dilute it appropriately.

What This Page Does Not Cover (and Where to Go Next)

• Specific recipes for advanced compost teas with added ingredients like molasses or fish hydrolysate.
• Detailed explanations of the specific types of beneficial microbes found in compost tea and their functions.
• Troubleshooting advanced brewing issues like persistent foul odors or lack of microbial activity.
• Commercial compost tea brewers and their specific operational guidelines.
• The science behind soil health and the role of microbial life in plant nutrient uptake.