It seems like compost tea has become all the rage in the past few years in the gardening community, and there is good reason for the hype! While scientific research is still catching up to the concept, the anecdotal evidence says that compost tea is a healthy way to feed your plants, nourish your soil, and improve the health of your garden microbiome.
So what is compost tea and what’s the best way to make it? Well, let’s dive into all things compost tea and find out!
What is compost tea?
In its simplest form (more on that in sec), compost tea is exactly what it sounds like! Tea that is steeped with compost instead of tea leaves. The resulting tea is then sprayed or poured onto plant leaves or into the soil to reach plant roots for easy absorption of all the nutrient goodness!
Compost tea and compost leachate are not the same. Compost leachate is the liquid that is released from a worm composting bin or other type of composting bin. This liquid has good nutrients, and can be used in the garden if harvested regularly.
What are the two different kinds of compost tea?
So now that we did an over-simplified definition, let’s look into the two main kinds of homemade compost tea and why you might want to use one over the other:
- Non-aerated compost tea (NCT): This is what we described above. Basically, you steep some compost (and maybe other ingredients) in some water to make an extract that you can then use in your garden. This extract can be sprayed, poured, or used as a soil drench. It can help you stretch small compost piles and help you more quickly distribute the nutrients in compost to your plants. The big hang-up is here is that this anaerobic environment is a happy space for harmful bacteria, fungi, and even mold. So your non-aerated compost tea can quickly become a scary science experiment.
- Aerated compost tea (ACT): Now this is where you’re really getting into the superpowers of compost tea, and this is the type of tea we’ll be talking about the most in this article. This is the same shebang as above, except you add air to your brewing process. Most folks do this through a small aquarium air pump. Why add air? Well, the aeration turns the tea into an aerobic environment, which helps promote the growth of healthy bacteria and other microorganisms in the brew. When the brewing process is complete, the beneficial microorganisms in your tea have expanded exponentially, making a powerful strength serum for your garden!
There are also a number of other kinds of compost tea—like plant tea (typically made by brewing a tea using plants like comfrey or nettle) and manure tea, which is yup, exactly what it sounds like (and smells like). Yay poop tea!
Benefits of Compost Tea
Any time you’re working with compost, you know one of the main benefits is going to be fertilizing that adds nutrients to your soil. But compost is also a playground for healthy microbes that are part of the tiny ecosystem that thrives in your soil. Healthy bacteria, mycorrhizal fungi, protozoa, and beneficial nematodes do tons of heavy lifting to keep your garden happy and healthy. Soil microbes decompose organic matter, process nutrients so they are available for your plants, protect from diseases, reduce pest pressure, and help fertilize the soil.
From a logistical standpoint, many gardeners find compost tea easier to work with and distribute among their plants. You can take a small amount of good compost and generate enough fertilizer for the entire garden. Plus, liquid fertilizers are easy to work with and are typically very quick-acting.
How often do you use compost tea?
This is something you’ll need to hash out in your own garden to see what works with your schedule and your plants. We use aerated compost tea every other week in the Growfully Gardens during the growing season. I know other gardeners who use it weekly, monthly, or even just a couple of times a growing season.
Does compost tea really work?
There isn’t a lot of scientific research on the tea itself—probably because compost tea is usually brewed on a small scale, and most scientific research is based on what would work for large-scale agricultural businesses.
But there is a lot of research on the importance of a healthy soil microbiome. And a ton of anecdotal evidence all over the internet from folks who have seen real improvement in plant health and production by regularly using aerated compost tea. And I’m one of them! I’ve seen huge results by regularly using it in my garden.
This is one of those “it won’t hurt anything” trials to take to your garden. In the worst case scenario, you’re out a few bucks on an aquarium pump and a few minutes of application time. In the best-case scenario, you have unlocked an affordable and easy fertilizer that revolutionizes your garden!
How fast does compost tea work?
Most liquid fertilizers are pretty fast-acting, and this one is, too! With well-brewed, aerated compost tea, expect to see some greening-up and improved growth within a week or two.
What do I need to make a compost tea brewer?
Making a brewer at home is super simple, and only really required two items—three if you’re feeling fancy. Here’s what you’ll need:
- A 5-gallon bucket. Any clean bucket will do the trick!
- A small aquarium pump. You’ll want a pump that comes with tubes and air stones. You can get by with using a pump with just one air outlet, but two is even better.
- A brew bag or small burlap bag (optional). This holds all your tea ingredients, making it easier to strain later. Totally optional, but definitely saves some headaches. Make sure to get a bag that has a 400-micron screen or LARGER. This is important to let all your beneficial microbes pass through. If you are using a brew bag, you might also want to grab a chip clip to attach the bag to the side of the bucket for easier retrieval later.
That’s it! You now have a compost tea brewer, and you’re ready to make your first batch of tea!
What ingredients do you need to make compost tea?
If you’re a regular organic gardener, you probably have most of the ingredients you already need hanging around your kitchen or garden shed.
- Unsulfured blackstrap molasses—this is food for the bacteria in the brew.
- Liquid kelp fertilizer and/or fish emulsion—this is food for the fungi in the brew.
- Finished organic compost or worm compost—this is your inoculant, and how you introduce your microbes to the brew.
- Non-chlorinated water—chlorine can kill the bacteria. Rainwater works great for this, but you can also filter your water, or just let it sit out for at least 24 hours before brewing.
There are as many compost tea recipes out there as there are people making it! This is our basic recipe, but if you want an even easier place to start, we’ve used Boogie Brew premade tea before with great results.
How to Make Compost Tea
Once you have your ingredients and brewer ready, making your own compost tea takes just a few minutes of active prep time:
- Set up in a room temperature spot out of the sun. Ideal temperature for brewing tea are between 65ºF and 75ºF. In your clean bucket, add the molasses, liquid kelp, fish emulsion, and compost.
- Fill the bucket with the non-chlorinated water—you’ll want to leave about 3-4 inches at the top.
- Hook up your aquarium pump and fit the tube with an air stone, and sink the stone to the bottom of the bucket.
- Turn on the aquarium pump, and it should start bubbling away! Brew for 24 hours. No need to stir or agitate—let the pump do all the work! After 24 hours, the mixture should be foamy, have lots of bubbles, and smell pleasantly yeasty or earthy like good finished compost. If it smells off, stinky, or rancid, toss it out, wash all your gear, and start over.
How long does it take to brew compost tea?
No matter if you’re aerating or not aerating, you’ll want to brew your compost tea for right around 24 hours. Any longer than that and it will be in danger of fostering some less-than-stellar bacteria like E. coli and salmonella. If it starts to stink, you probably are harboring some nasties and need to toss it out. Good compost tea won’t smell!
Do you need to dilute compost tea?
Most people dilute compost tea to a ratio of 4 parts unchlorinated water to 1 part tea, but you can also use undiluted tea straight—which can be especially helpful when dealing with a particularly sick or struggling plant. Use an even more diluted ratio (10:1) for regular maintenance fertilizing.
How do you use compost tea?
Apply the tea by spraying soil and plants with a pump sprayer, pouring on using a watering can, or drenching the soil at the base of plants. Compost tea works well as a fast-acting foliar spray, so we tend to apply it with a backpack sprayer in the Growfully Gardens.
Can you give your plants too much compost tea? Or even kill your plants with it?
Properly made aerated compost tea can be used in abundance! You can’t really overuse it. However (and this is a big however), compost tea that harbors bad bacteria and other microbes can very much harm—and even kill—your plants. That’s why we prefer the aerated compost tea method, which reduces the chances of harmful microbes taking over, and we recommend you only use compost tea that smells pleasantly yeasty or earthy. Any off-smelling tea should be promptly discarded.
How to Make Compost Tea
There are as many compost tea recipes out there as there are people making it! Below is our basic compost tea recipe, but if you also want an easy place to start, we've used Boogie Brew premade tea before with great results.
- 1 tablespoon unsulfured blackstrap molasses
- 2 tablespoons liquid kelp fertilizer and/or fish emulsion
- 2 cups finished high-quality compost or worm compost
- Non-chlorinated water
- Clean 5 gallon bucket
- Brew bag (optional)
- Chip clip (if using a brew bag)
- Small aquarium pump
- Watering can or backpack sprayer
- Fine mesh sieve or cheesecloth (if using a sprayer but no brew bag)
- Set up in a room temperature spot out of the sun. Ideal temperature for brewing tea are between 65ºF and 75ºF.
- In your clean bucket, add the molasses, liquid kelp, and fish emulsion.
- If using a brew bag, fill it with the compost, close, then place in the bucket. Attach brew bag to the side of the bucket with a chip clip for easy retrieval later.
- If not using a brew bag, add the compost to the bucket.
- Fill the bucket with the non-chlorinated water—you'll want to leave about 3-4 inches at the top.
- Hook up your aquarium pump and fit the tube with an air stone, and sink the stone to the bottom of the bucket. If you have a second outlet on your pump, fit the second tube with an air stone, and place it in the brew bag (if using), or use a chip clip to float it toward the upper portion of the tea.
- Turn on the aquarium pump, and it should start bubbling away! Brew for 24 hours. No need to stir or agitate—let the pump do all the work!
- After 24 hours, the mixture should be foamy and smell pleasantly yeasty or like good finished compost. If it smells off, stinky, or rancid, toss it out, wash all your gear, and start over.
- If you used a brew bag, remove it. If you didn't use a brew bag, you can use the tea in a watering can with an open nozzle or as a soil drench. If you want to put it into a sprayer and use it, you'll need to strain the tea through a fine-mesh sieve or cheesecloth first.
- Apply the tea by spraying soil and plants with a sprayer, pouring on using a watering can, or drenching the soil at the base of plants. Most people dilute compost tea to a ratio of 4 parts unchlorinated water to 1 part tea, but you can also use undiluted tea straight—which can be especially helpful when dealing with a particularly sick or struggling plant. Use a more diluted ratio for regular maintenance fertilizing.
- Make sure to thoroughly clean all your equipment before storage.
Hi Cassie! I’ve had a backpack sprayer before and while I like the ergonomics of it, it didn’t last long. Can you comment on how you store and/or clean yours?
We don’t store anything in ours in between use—we transfer whatever is left to a glass container or container designed for whatever fertilizer/treatment we were using. It also can’t hurt to give it a good rinse after use!
Common sense, right?!
How long have you had your backpack sprayer?