The advantages of using compost tea to fertilize your garden include easy application, increased root growth, better soil biodiversity, and disease suppression. Compost tea is also incredibly easy to make!
Supplementing your garden’s success with this agricultural superfood should be a no-brainer for the savvy gardener in all of us. Going forward, we’ll discuss these benefits in more detail with the help of a few scientific studies to validate our claims.
What is compost tea?
Compost tea is a soil amendment made from the best fertilizer one could apply to their crops, compost. So as the name suggests, compost tea is made by steeping said compost in water for about 24 hours. Molasses and dissolved oxygen are also common additives for aerobic compost teas to further promote the development of beneficial microbial communities.
Over time, nutrients from the compost (ie. Nitrogen (N), Phosphorus (P), Potassium (K), etc.) and a host of beneficial microorganisms will leech into the water. Note that this process is intended to drain just a fraction of the original compost’s nutrients.
This makes compost tea a lighter alternative that is less bulky to transport and is easier to apply in large quantities.
Compost tea is simple to make, transport, and apply
What makes compost tea so easy to brew is that most teas are made with very few ingredients. At its core, the bare essential ingredients for anaerobic compost teas (without oxygen) are simply compost, water, and some kind of mixing mechanism. While anaerobic teas lack the diversity of microorganisms compared to aerobic teas, the nutrients will transfer just as well as any other method. Aerobic compost teas require a few more ingredients like air bubblers to force oxygen into the water and molasses to feed the microbes, but the basic premise remains.
After brewing the concoction, the trouble of transportation boils down to finding a watertight vessel to contain it. Unless you plan on spraying your fertilizer through a machine or a showerhead nozzle, then don’t bother straining your garden tea. While dirt chunks and twigs are common features of compost tea these will not inhibit its effectiveness and your garden will accept the extra nutrients regardless.
Applying your water-soluble fertilizer is as simple as pouring it directly over the crop’s root zone.
You can also use compost tea as a foliage spray to suppress certain fungal diseases and pests from damaging the garden.
I recommend that for anyone who goes the foliage spray route to protect their eyes and mouth from the spray. While compost tea is organic, there are still microorganisms swimming around in there that I would not recommend ingesting or showering in for sanitation reasons.
Compost tea stimulates foliage and root growth
Applying compost tea stimulates foliage and root growth. Those results are observed in these two studies:
- Effect of Aerated Compost Tea on the Growth Promotion of Lettuce, Soybean, and Sweet Corn in Organic Cultivation. Link
- Compost tea at a concentration of 0.4% showed the most effective growth for root and foliage parameters in red leaf lettuce
- Concentrations of 0.8% showed significant root stimulation in sweet corn and soybean crops
- Soybean plants treated with higher concentrations of compost tea experienced root nodule formation about 700% higher than plants from the control group
- Bacteria were the most dominant microorganism out of all the anaerobic compost teas, regardless of the original compost’s composition.
- Effects and relationships of compost type, aeration and brewing time on compost tea properties, efficacy against Pythium ultimum, phytotoxicity and potential as a nutrient amendment for seedling production. Link
- This study observed significant inhibition of mycelial growth in the fungus, P. ultimum, through both aerated and nonaerated tea treatment. Furthermore, fungal suppression was significantly higher from teas made with lawn clippings.
- All the tested compost teas stimulated seed germination in tomatoes and root growth in sweet peppers
- After treatment with a nonaerated tea brewed for 168 hours, dried organic matter in tomatoes increased by 122% compared to the control group.
- The data showed that while aerobic and nonaerobic tea did not significantly differ in nutrient content, there was a significant difference in effective fungal suppression, in favor of aerated tea.
In my research, I found similar results in crop growth, even in studies that primarily focus on disease suppression.
Especially in the second study, compost tea outperformed chemical fertilizer, establishing its viability as an effective fertilizer in an organic agriculture setting.
These are exciting results for anyone looking for a sustainable alternative to chemicals fertilizers.
Compost tea fights off disease
The secret to how compost tea helps fight off disease in your garden lies in the biodiversity of microorganisms that the tea is brewed from. These effects are the most potent in aerated compost tea. If you are looking to brew a disease-fighting garden tea, consider investing in some molasses to feed those beneficial bacteria and a few bubblers to oxygenate their water.
By cultivating diverse colonies of beneficial bacteria, you create an environment where microorganisms have to compete for space and nutrients. Now, instead of pathogens feeding off of your hard work, they will be too busy trying to survive the onslaught of antagonistic bacteria, predatory microorganisms, and growth-inhibiting chemical compounds.
Here are what scientists have to say about the suppressive capabilities of compost tea on common produce pathogens:
- Bio-potential of compost tea from agro-waste to suppress Choanephora cucurbitarum L. the causal pathogen of wet rot of okra. Link
- Two compost teas were tested for this study. One tea was brewed from compost made from rice and straw, while the other contained palm oil tree litter and empty fruiting bodies
- When tested on a petri dish culture of fungus, both of these teas inhibited mycelial growth by 100% when left unsterilized by filtration or heat.
- The disease-fighting potential of these teas was significantly reduced when filtered through a millipore membrane or exposed to extreme heat.
- When sterilized with extreme heat, the compost tea performed statistically insignificant to the control group, which was treated with plain water.
- Despite the study’s initial results, treatment resistance was observed after excessive spraying, so the authors recommend spraying in short intervals to prolong the tea’s disease-suppressing qualities.
Compost tea has its disadvantages
To play devil’s advocate, let me clarify that compost tea is not a miracle cure-all without flaws. Here is are a few areas where compost tea falls short or could be improved on.
- Aerated compost has a short shelf life and will begin to spoil within 48 hours
Unlike commercial chemical fertilizers, you cannot store compost tea for extended periods without it spoiling. Especially for aerated teas, oxygen levels tend to plummet 24- 48 hours after brewing.
Once the oxygen dissipates, the tea will become anaerobic. This environment promotes the growth of harmful bacteria that you don’t want to spray on your plants. For these reasons, always plan on using your compost tea immediately after steeping or within 24 hours.
- Compost tea effectiveness is completely dependent on the quality of the original compost.
This is a simple premise of good in, good out. You can make compost from any dead organic material, and the tea that you make will reflect the quality of the compost it is brewed from.
Never expect your compost teas to be any more nutritious than the original compost, aerated or not. Compost tea only serves as a diluted form of compost that requires periodic spraying for maximum effect.
- Brewing compost tea can produce highly variable results
Compost teas are like snowflakes, no two are alike. Between the variability in microbial communities, nutritional content, and C:N ratios, it is very difficult to brew consistent batches of garden tea. Even if you managed to track the chemical composition of every input down to the micronutrient (why would you do that?) you cannot control the rate that those nutrients transfer into the water or the microorganisms that live there.
Speaking of microorganisms, scientists estimate that around 10 billion microorganisms from thousands of different species exist in every gram of soil. At the time of this article, there is little knowledge on the specific mechanisms that make compost tea so effective at disease suppression. In their words,
“However, it is not clear whether pathogen inhibition is due to parasitism, competition for nutrients and colonization sites, or if applied organisms produce antibiotics in situ once established on plant surfaces.”
Bio-potential of compost tea from agro-waste to suppress Choanephora cucurbitarum L. the causal pathogen of wet rot of okra. Link
Yasmeen Siddiqui et al.
Conclusion
Those are the massive benefits of fertilizing your garden with compost tea. Applying compost tea helps your plants grow fuller, stimulates their root growth, and helps fight off common crop pathogens. It is also incredibly simple to brew and easy to apply, so why not give it a try this growing season? Compared to other commercial fertilizers, the range of nutrient and disease-fighting capabilities can’t be beaten. It’s good for your plants and good for the planet, so why not give compost tea a try this gardening season? Your garden will love it!
Sources:
- Kim, Min Jeong et al. “Effect of Aerated Compost Tea on the Growth Promotion of Lettuce, Soybean, and Sweet Corn in Organic Cultivation.” The plant pathology journal vol. 31,3 (2015): 259-68. doi:10.5423/PPJ.OA.02.2015.0024
- Yasmeen Siddiqui et al. “Bio-potential of compost tea from agro-waste to suppress Choanephora cucurbitarum L. the causal pathogen of wet rot of okra.” Biological Control, Volume 49, Issue 1. (2009): Pages 38-44, ISSN 1049-9644
- C. C.G. St. Martin et al. (2012) “Effects and relationships of compost type, aeration and brewing time on compost tea properties, efficacy against Pythium ultimum, phytotoxicity and potential as a nutrient amendment for seedling production.” Biological Agriculture & Horticulture, 28:3, 185-205, DOI: 10.1080/01448765.2012.727667