It’s time to get into the how-to behind one of my all time favorite gardening tools: compost tea.
If you’re not familiar with compost tea, the particular method of tea we’re making here is known as ACT (Aerated Compost Tea). ACT is created by soaking quality compost in a container of water and then extracting the water soluble nutrients and beneficial microorganisms from the compost and into the water through heavy aeration. Food is then added to the water for the microorganisms to feed on, causing them to rapidly multiply. The result is an aerobic slurry of soluble nutrients and beneficial microorganisms which can be applied to your grow environment to add life to your plants and your soil.
Compost tea is safe, effective, and adjustable to suit your needs. The compost it utilizes can be produced for free from your own backyard, so it’s affordable too!
My Compost Tea Setup:
To start, let’s go ahead and walk through the various components of a compost tea setup:
Container: Probably the most important piece of this setup; it really holds everything together 🙂
A regular five gallon bucket is the most ideal container, in my mind. Five gallon buckets are cheap and easy to come across, plus very well rounded in shape, making them less prone to dead spots and easier to keep well aerated. Square shaped buckets should be avoided for this reason. To find more free buckets than you’ll ever need, periodically check the bakery section at your local grocery store. The icings and fillings that bakeries used in their baked goods come in five gallon containers and are often thrown out after emptied.
Air pump: My personal air pump is a 60 watt model designed by Hakko. When you’re buying an air pump for making compost tea, it can be tempting to go with fish aquarium aerators but these just don’t provide enough aeration for a quality brew. To properly brew compost tea, you’ll need an air pump that produces a bare minimum of .05 cfm (cubic feet per minute) per gallon of compost tea. For a five gallon system, that’s a minimum of .25 cfm (.4 cfm is far preferred).
Air distribution: Besides the hose carrying the air from my pump to my bucket, the next part is the air distribution. Many people seem to want to go with air stones for distribution, but I’m quite against these, as they clog up with the bio-slime that’s a by product of the brewing process. This slime can encourage anaerobic activity in your brew, so it’s best to avoid surface areas that are hard to clean. Instead of an air stone, I opted to custom build my own air distributor out of pvc. It’s basically an octagon made out of small pvc pieces and 45 degree joints with 1/16″ holes drill all around the inner perimeter. It’s easy to clean and provides even aeration, which helps eliminate dead spots in the brew.
Tea Bag: If you’re planning on applying your compost tea foliarly, then you’ll need to be able to contain your compost. Without a mesh bag, the compost particles that are in your tea can easily clog the tiny pores on spray applicators. The optimal mesh size for a tea bag is 400 microns; any smaller and you begin to block beneficial fungi from entering your tea. Some companies sell 400 micron tea bags specifically for brewing compost tea.
If you’re not interested in purchasing a bag specifically designed for compost tea, I’ve also heard paint strainer bags work quite well for compost tea.
The Brew Process:
Once you’ve got all of the pieces of your setup assembled, you’re ready to begin!
First, flip on your air pump, fill your 5 gallon bucket with water and let it aerate for a solid 15 minutes. Water from stagnant sources like rain barrels are often deprived of air and the extra aeration time will ensure the brew is charged with oxygen from the start.
While you’re waiting for the water to aerate, go ahead and take that time to collect your compost for the tea. 1 lb of fresh, clean compost or worm castings is usually an appropriate amount.
You’ll also have time to measure out your microbe foods. Common microbe foods used in compost tea are black strap molasses, kelp powder/seaweed extract, humic acid, and fish hydrolysate. Experimentation is important when it comes to your microbe foods, as they have a large impact on the quality of your brew. For some good compost tea recipes, you can check out these websites:
Once your water has been aerating for 15min, go ahead and add your compost and your microbe foods. If you’re using fish hydrolysate, I highly recommend adding it first before any of your other ingredients. The oils found in the fish product dramatically cut down on the foaming produced by the kelp and molasses. Your compost tea ingredients should be mixed with water separately before adding to your compost tea to ensure they are properly dissolved and incorporated. If you’re brewing indoors, I also recommend placing your brewing container inside of a larger bin. The foam and churning water can make quite a mess!
After you’ve added your microbe foods, let your tea brew for anywhere from 12 to 48 hours, checking in on it periodically to make sure that everything is smelling good and clean (a little bit of fish smell is okay if you used the hydrolysate in your brew). The exact amount of brew time will heavily depend on size of your container, the amount of microbe foods you added, and the power of your aerator. As the beneficial organisms in the brew begin to multiply, they use up the oxygen in the water. Keeping the aerator running ensures that your water can support a lot of healthy microorganisms, but eventually they will reproduce to the point where they will even use up the air that the aerator is providing. A that point, the tea begins to go anaerobic and can start providing conditions favorable to microbes that are potentially harmful. Many of the common pathogens found in the food industry are anaerobes, meaning they prefer environments with less oxygen, so it’s recommended not to utilize tea that is anaerobic for growing food.
Going a step beyond the sniff test, you can periodically examine samples of your compost tea under a microscope to check for signs of anaerobic activity going on in your brew. Getting a microscope is optional, but it’s a really great way to determine the quality of your tea, making it a valuable tool for experimentation.
Once you decide that your tea is complete, turn off the aerator. Because compost tea is a living, biological product, it doesn’t keep well after the air is turned off, so make sure you use it within 4-6 hours once you turn off your pump.
Applying Your Tea:
Properly brewed compost tea is completely safe for your plants and can be applied straight or diluted in any amount (as long as you’re not drowning your plants). How much mileage you can get out of diluting your compost tea will depend on the quality of your brew, but a 1:1 ratio of tea to water usually works great. Compost tea can be used as a soil drench and applied foliarly as well
Compost tea takes some experimentation, but if you’re willing to tinker with it, you’ll find yourself creating a useful, safe product that will nourish your plants and boost the diversity of microorganisms in your grow environment. For more information on compost tea, check out the websites I linked to in the microbe foods section, and take a look at the compost tea yahoo group, as well as the comment section below for support and questions!
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