What’s Brewing? Podcast Episode 9: What is Compost Extract?

What’s Brewing is a podcast all about compost tea hosted by Troy Hinke.

Troy Hinke served as Rodale’s Compost Research Specialist alongside the founder of Soil Foodweb Inc., Dr. Elaine Ingham. Troy now runs Living Roots Compost Tea, where he offers several services including consultations, compost sprays, and compost brewing, among others.

Episode nine of a 10-episode series on compost teas, host Troy Hinke talks about compost extract: what it is and how to make it.

Compost Extract vs. Compost Tea (01:05)

Compost extract is similar compost tea in that they are both biological inoculants. The difference is that compost extract contains a lower population of microorganisms than compost tea.

The number of organisms you can extract from the surfaces of the compost that you are using is what you’re going to start with. So, say you have a hundred thousand microorganisms, you’ll hopefully extract a hundred thousand microorganisms from that compost into the water, and then it’s ready for use. With compost tea, we add microbial foods to get those 100,000 microorganisms to multiply to millions and billions before it’s ready for use.

The materials needed to make compost tea are the same materials needed to make compost extract, save for the microbial foods. After extracting the microbes from the compost and into the water, it’s ready for use.

While compost tea is best used for foliar applications, compost extract is better for soil application.

How Do We Make Compost Extract? (03:13)

Just like for making compost tea, we need a clean container, clean water, compost or vermicast, and then a brew bag.

The first step to making compost extract is to fill the clean container with clean water, but unlike in making compost tea, the water temperature isn’t as important, as we aren’t getting the microbes to reproduce.

That said, we’ll still off-gas any chlorine or chloramine from our water. Letting the water sit out for 24-48 hours will get rid of the chlorine or chloramines, but if you can cut the time down to 12 hours by using an air pump or a bubbler.

Next, we fill up the brew bag with compost using the same measurements as we would make compost tea. As with compost tea, it’s best to make use of compost of varying ages to get a good diversity of microorganisms.

Compost Extract VolumeCompost Volume
5 gallons2-4 cups
50 gallons1 gallon (16-18 cups)
100 gallons< 2 gallons (28-30 cups)
1000 gallons6-8 gallons

After the brew bag is filled, we place it in the water and agitate and massage the compost, making sure to break down any large clumps and get as much surface area as possible. We can work the compost by squeezing, pushing it against the sides of the container, swirl it, and shake it to get the most biology out of it.

As far as massaging and agitating, it’s best to massage the compost for a good 3-5 minutes and agitate it for 5 minutes or put it on air for up to 12-24 hours. The more we agitate the compost, the more we’ll get out of it. Some fungal hyphae cling tightly to material, so agitating the compost will help get those hyphae into the extract.

After we’re finished agitating, we’ll run the extract through a filter to get rid of the sediments, and then we’re good to go.

A Trick with Compost Extract (07:28)

If you want to increase the number of microorganisms in your extract, you can fill up your brew bag more than once. After agitating the compost in the water, you can replace the compost with a new batch to get double to population of microorganisms.

That said, you wouldn’t want to keep doing this repeatedly because at a certain point, you’re going to have so much sediment buildup in the water that it might possibly cause issues with clogging filters on spray equipment. But if spray equipment isn’t an issue, then feel free to keep going.

Adding Microbial Foods? (09:14)

If, for some reason, you’d like to add microbial foods, then save yourself the extra work of scrubbing the brew bag by adding them in after the agitation process and after the filtering process. Add them in the spray tank so that you’re directly feeding the microorganisms from your extract.

Benefits of Compost Extract Over Compost Tea (10:05)

Compost extract can be used immediately. If, for whatever reason, you immediately need a biological inoculant to put on your plants, and you have no time to brew compost tea, then you can whip up compost extract in a few minutes.

Another benefit is that you don’t have to worry about it brewing too long and going anaerobic. When brewing compost tea, and you hit peak microbial populations, it will start to become anaerobic, and the anaerobic populations will begin to take over. You don’t have that worry with compost extract because the microbes don’t reproduce and won’t hit that peak population.

Compost extract also has a longer shelf life compared to compost tea due to the lower microbial count in the water. Because the microbes aren’t reproducing, the oxygen won’t be used up as quickly, either.

“You can keep things a lot simpler on a farm with minimal communication or volunteers and just use compost extract. It makes it a lot easier for everyone involved.”

A Recap of Some Compost Extract Uses (14:15)

            -Soil soaks (for agricultural and landscape applications)
            – Seed soaks
            – Hydroponics
            – Irrigation needs
            – Keep cut flowers longer
            – Sprout and microgreens production

Overview (16:32)

Compost extract is made the same way compost tea is, except that (1) we’re not adding microbial foods; and (2) we’re not brewing to increase those microbial populations. We are simply putting compost in a brew bag, putting it in water, and then agitating it to extract or pull the microorganisms from the surfaces of that organic matter.

Compost extracts can be used immediately without having to wait to brew, which is one of their advantages. Compost extracts will also have lower populations of microorganisms than compost tea. And lastly, compost extracts won’t contain any sticky residues from microbial foods, making them more ideal than compost tea for irrigation needs.

Learn More

Learn more about Troy Hinke and his work on compost teas over at Living Roots Compost Tea, Instagram, and Facebook!

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