How to Make Compost Tea
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As an organic giant pumpkin grower, one of my biggest goals is to create a rich soil that is loaded with beneficial organisms. One way I do this is by adding mycorrhizae and nitrogen-fixing bacteria to the soil when I bury the vines. Another thing I do is make compost tea once a week. Compost tea is a brew of compost and water that is full of nutrients and contains a diverse population of bacteria, fungi, protozoa, and nematodes.
There are many ways to brew compost tea, but they all have the same goal of trying to promote microbial growth. Microbes need food and air to thrive, so you need to aerate the tea and provide a food source for the organisms. I learned my method from Don Langevin’s book, How to Grow World Class Giant Pumpkins the All Organic Way. It is very basic and involves a 5 gallon bucket and an aquarium air pump. If you don’t want to build one yourself, you can buy a pre-made brewer setup and pre-made compost tea bags.
Step #1 is to build your brew system. You need the following materials:
Aquarium air pump with 2 outlets
Two T-connectors
25′ length of aquarium hose (1/4 inch)
One-gallon strainer bag
Twine or rope to hold up your strainer bag in the bucket
I used the video below to guide me through building my compost tea brewer. I don’t use a lid like he does.
Now it’s time to brew your tea. The recipe requires the following:
1 pound worm castings (to go in strainer bag)
2 oz humic acid
2 oz unsulphured molasses (this is the sugar supply for the microbes)
Set up your brew system as follows:
Fill your 5 gallon bucket with water. I try to use rain water since the water from my hose is chlorinated and may affect bacteria levels.
Add the humic acid, fish/seaweed fertilizer, and molasses to the bucket. I use this to measure everything out.
Fill the strainer bag with 1 pound of worm castings.
Place the one-inch air stones into the strainer bag and work them into the worm castings. The air will help move the microbes from the worm castings into the solution. Tie the bag closed with some rope or twine and place in your bucket. Hold the bag up by tying it to the bucket handle, making sure not to let the bag touch the bottom of the bucket.
Place 5-inch air stones into bottom of bucket.
Hook up to you air pump and let brew for 24 hours!
After 24 hours it’s time to apply your compost tea to your garden. I use a pump sprayer, but I remove the filters on the tube and screw off the end since they tend to clog up on me. Before pouring the compost tea into the sprayer, I strain it through a cloth to remove any biofilm or debris that might clog up my sprayer. The sprayer I use is 2 gallons which means I have to refill it multiple times. I would recommend getting a bigger backpack sprayer so you can do it all in one trip. Some of these have external filters to prevent any debris from clogging up the system, but be aware that if they don’t, they may contain internal components that can get clogged up.
Straining out the tea so it doesn’t clog up my sprayer.
You can apply the compost tea to the soil or use it as a foliar spray. I typically apply it to the soil since that is what I’m trying to build up. I always apply it the day after I start brewing it. Even after 24 hours there is a huge amount of biofilm accumulated on the air stones!
Look at all that biofilm after just 24 hours!
How to get a microbiologist excited.
Once you have applied all your compost tea, water it in to make sure the organisms penetrate down into the root zone. I spread the used worm castings around my pumpkin patch and then clean my supplies, making sure to collect any leftover debris into a bucket to spread over my patch as well.
And that’s it! Wishing you some happy plants and big pumpkins!
Update: I now use a fertilizer injector to apply the compost tea. This allows me to siphon the tea directly into the hose so I can water it right into the soil without having to transfer, lift, or filter anything. This will only work if you have a high amount of pressure running through the hose. I use a fireman’s style hose nozzle. If this ever starts to get clogged, I just loosen the nozzle which release the clog. The Amazon reviews recommend drilling a hole in the bottom to prevent it from getting clogged.