What is compost tea?
Compost tea is a bit of a misnomer. Tea is technically an infusion that requires heating up water to boiling and pouring it over herbs to create a healthful drink. While compost tea is like a healthful drink for plants, it should almost be called compost beer because the process is closer to fermentation. It is a brewed liquid that concentrates bacteria, fungi, protozoa, and hopefully nematodes into an easily absorbed liquid form.
There are two schools of thought on brewing, and one of them involves throwing compost into a bucket of water, letting it sit, and hoping for the best. This is generally just called compost tea and it has a whole group of fans who swear by it. The second method is aerated compost tea, which requires oxygen and agitation. It’s a little more work, with a lot less smell.
What are the benefits?
While there are only a handful of studies that have researched the benefits of compost tea, without any true conclusions, there are thousands of gardeners who swear by it from their own personal experience. According to the many different articles published by various university extensions, compost tea used in conjunction with other good gardening habits creates healthy plants.
In an article analyzing compost tea, Dr. Linda Chalker-Scott, Extension Horticulturist and Associate Professor at Puyallup Research and Extension Center, Washington State University, stated, “There is no ‘silver bullet’ for plant health problems caused by poor soil health and improper plant selection and management.” But, she admits that compost tea has been shown to suppress pathogens in some plants.
For those who have experienced the benefits of compost tea, the results are clear due to two things it seems to do very well:
- Improving the nutrients in the soil. This seems like the most obvious benefit, because it is made of the same basic ingredients as compost (or is made from compost).
- Increasing the population of mycorrhizal fungi and predatory nematodes, both of which help defend plants against a variety of microorganisms.
By doing these two things, compost tea can help plants grow faster, increase yields, and improve their overall health, decreasing the number of pests and disease they experience.
How long does it take to brew compost tea?
It only takes about 24-36 hours to make either kind of compost tea noted above. Any longer than that and your concoction will be in danger of collecting some not-so-friendly bacteria like E. coli and salmonella. The microbes within will use up all the oxygen, which creates anaerobic conditions, and increases the likelihood that bacteria, viruses, and molds will thrive.
What is aerated compost tea?
Aerated compost tea, also known as aerobic compost tea or actively aerated compost tea is exactly what it sounds like: regular compost tea that is mixed with a lot more oxygen. The theory is that if microbes use up oxygen quickly, which begins to create anaerobic conditions, then aerating the compost will produce larger populations of good organisms faster and prevent the bad ones. This is done by using an aerating pump like the ones used in fish tanks to create a bubbling action in the liquid.
What other types of compost teas are there?
- Plant tea: Instead of soaking compost, a plant that has nutritious properties is soaked in water to extract those nutrients. The most common plants used are comfrey and nettle, which can add valuable nutrients like phosphorus and potassium to the soil.
- Manure tea: This is a very common fertilizer used by farmers, which is a mixture of various aged manures soaked in water. It’s not really the best home project as it becomes very stinky.
- Commercial microbial tea: Just add water! These instant tea mixes are usually designed to combat specific plant issues, but proponents of homemade compost tea believe that they do not have enough microbes to be worthwhile. However, they are technically much safer because they are free from bad bacteria.
- Compost leachate: There is a fine line between compost leachate and regular compost tea, because both require compost to sit in water. However, leachate is created when water leaches through vermicompost (worm compost) or your compost bin and out the bottom. Because it’s not fermented, it is considered to be only valuable for the nutrients it contains, rather than the living microbes. The Green Cone, a solar waste digester, is one such composter effective at creating nutrient-rich leachate for surrounding plants.
What are inoculants and do you need them?
When compost tea brewers refer to inoculants, they are referring to ingredients that encourage the growth of microbial inoculants, or soil inoculants, which includes any kind of microbe that helps plants. These usually fall into two categories: bacteria and fungi. The bacteria can fix nitrogen and break down inorganic soil phosphates, and the fungi live with host plants and improve the soil conditions. So, long story short, you do need inoculants if you want to experience the true benefits of compost tea, but they come from worm bin castings or high-quality compost, which is the main ingredient anyway. If you make the compost tea right, you’ll hopefully have the inoculants that you want.
Best Compost Tea Recipe for Boosting Plant Growth
All compost teas follow the same basic recipe.
Ingredients and Supplies
- Non-chlorinated water (use rainwater, or allow tap water to sit for over 24 hours)
- 1-2 cups of inoculant (either worm castings or compost)
- ¼ – ½ cup of food source for bacteria or fungi
- 5 gallon bucket
Bacteria need simple sugars and proteins, and usually one of the easiest sources is unsulphured molasses. Fungi need more complex sugars, with common sources including fish hydrolysate (essentially ground up fish), kelp/seaweed, and humic acid.
Many people create a mixture of both molasses and fungi food to create a good balance of nourishment for both fungi and bacteria, and it may come down to what you have readily available.
If you want to avoid purchasing chemical products like humic acid, a great recipe includes:
Easy DIY Compost Tea Recipe
- Non-chlorinated tap water (enough to fill a 5-gallon pail)
- 2 cups fully finished organic compost (it should smell nice!)
- 1 tablespoon unsulfured blackstrap molasses
- 1 tablespoon liquid kelp fertilizer (or soak kelp meal in water)
- 1 teaspoon liquid fish fertilizer
Building a DIY Compost Tea Brewer
For the simplest kind of compost tea brewing, all you need is:
- A 5 gallon bucket
- Porous fabric, such as a nylon stocking or porous cloth for filtering the compost
- Enough non-chlorinated water to fill the bucket
- A sprayer or plastic watering can
For aerated compost tea, you will need everything above, plus:
- An air pump
- An airstone (aquarium bubbler)
You can make your own non-chlorinated water by collecting some rainwater or simply letting tap water sit for 24 hours. Fill up the bucket, and when it’s ready you can add the inoculant.
Many people dump the compost straight into the bucket and then just strain it through a burlap bag to separate the tea from the solids. However, it’s easier and very little work to put the ingredients into a nylon stocking or porous cloth tied into a bag. Make sure you have a rope or long end to pull it up so you don’t have to put your hand in the tea. If you are using an air pump, drop in the airstone and fire up the air pump.
Now, let it sit for about 24 hours. Too much longer than that and bad bacteria will start to take over. In fact, if it starts to stink then you’ve gone too far and it needs to be thrown out. Once you’re ready to use it, your tea needs to be used within four hours so that the active microorganisms won’t start to die.
If you want to brew a larger batch, a hybrid compost tumbler-rain barrel works very well.
How do you apply compost tea?
It is usually recommended to dilute the tea to at least a ratio of 1:4 – or 4 cups to 1 gallon, and many people use a ratio of 1:10. You can apply your tea directly to the soil with the sprayer or watering can, or you can also use it as a foliar spray. Foliar feeding is mostly helpful in boosting the health of plants that are sick or infested. More than one application is necessary to see real results, and most people recommend at least bi-weekly.
Is your tea working?
If you have access to a 400X magnification microscope you can see the microbes yourself. Look into the diluted solution and you should be able to see thousands of bacteria and hopefully a helpful nematode. Every now and then you should also find an amoeba and flagellate.
But how quickly will your compost tea work? Most fans of compost tea have done their own side by side test, adding compost tea to one plant and not to an identical plant right next to it. While you won’t see immediate results, as time passes you will see a clear difference between the two. One will appear healthier, more vibrant, leafier and possibly have a higher yield. However, it will only happen with routine application over the growing season.
Have you had great results with compost tea? Share your tea experiments below!