Compost tea has been lauded as an organic elixir to prevent diseases and add more nutrients to plants. But how true is this, and can they be stored for a long time?
Compost tea has a very short shelf-life, from a few hours to less than a week. It is unsuitable for storage due to the microbes contained in the liquid, which may grow in abundance along with harmful bacteria. This is why it is best used immediately once it is ready within 24 hours.
Below, I talk about this in more detail, along with several things you need to know before using it:
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Table of contents
What is Compost Tea?
It is a liquid made from steeping compost in a porous bag inside a bucket of water. It’s often used as an organic fertilizer due to its high nutrient content and has also been said to prevent plant diseases. Some people also use animal waste like worm castings or plant matter like comfrey (a perennial herb) to make this ‘tea’. Essentially, it’s a giant version of making tea, but not the drinkable kind.
There’s also another form of compost tea called ‘compost leachate’, which is somewhat different. It involves collecting the fluid produced during the composting process and diluting it before applying it in the garden. But for this article, I’ll be specifically talking about the steeped compost tea version.
There are two types of compost tea: aerated and non-aerated. The latter is a simple set-up of soaking a compost-filled permeable bag in water overnight or for a few days. The mixture stinks the longer you leave it, so gardeners tend to use it immediately after 24 hours. Over the years, several scientific research projects have shown that this non-aerated/non-aerobic compost tea can reduce disease in (some) plants.
However, the aerated type can get a bit more complex. It needs an air pump to provide oxygen for the microbes and requires ‘feeding’ in the form of sugars such as molasses. If you browse the many gardening recipes on the internet, you’ll quickly see how fussy the process is. Some say you must use it within a few hours of brewing to “maximize” the fungi and bacteria available to enrich your garden.
I’m not a microbiologist or a soil scientist, so I wanted to figure out what to do with this information. I dug around to see if science can back up the claims about this ‘aerated/aerobic compost tea’. And well, here’s what I found out:
- There’s no observable difference in growth or reduced disease issues on plants when using water or aerated compost tea side-by-side.
- Some plants exhibit more disease problems when treated with aerated compost tea.
- Due to the active brewing process of aerated compost tea, it has been found to carry pathogens such as E.coli and salmonella.
It seems that aerated compost tea is more trouble than it’s worth. But there are people out there who will vehemently disagree with me. For the record, I am not disregarding gardeners who have seen success when using it on their plants, whether homemade or purchased.
But here’s the thing: each person will likely have different compost with distinct quality and nutrient levels. This results in compost tea that is extremely useful or entirely useless – so it makes sense that it works for one person but not with another. Despite that, the available but limited scientific literature or research on it has yet to say it’s worth the time and effort compared to non-aerated/non-aerobic compost tea.
Cautions on Using Compost Tea
If you still choose to make compost tea and use it on your plants, here are some things to keep in mind:
- Clean and sterilize equipment used to make compost tea thoroughly before and after use. You want to ensure you don’t cross-contaminate your batches and encourage good AND bad bacteria and fungi growth.
- Use compost tea in moderation, at most once a week. This is mainly to prevent runoff, especially during the rainy season. Just because it’s organic and natural doesn’t mean it is safe for the environment in excess because it can still cause water pollution.
- Do not apply compost tea to edible plants, only to ornamental plants. This is especially important if you’re using the aerated/aerobic kind. It’s really risky because they can carry E.coli and salmonella, so it’s better to err on the side of caution.
- Apply compost tea directly to the soil around the plants. You have to avoid wetting the plant’s leaves when using this mixture. Otherwise, you may unintentionally increase the risk of foliar diseases.
- Do not store compost tea – use it within 24 hours of soaking or ‘brewing’. The longer you leave it out, the smellier it becomes. If that isn’t enough to convince you, you may end up harboring some pretty nasty pathogens that’ll be detrimental to your plants’ growth.
- Do not use compost tea as a solution for plant problems. It’s not a miracle solution to make your plant better. Check whether there’s a problem with the soil, overabundance of chemicals such as fertilizers or pesticides, planting, overall care, and plant quality. It’s always best to go back to basics and see what’s wrong with your plant first before jumping to conclusions.
If you’d rather not get on the bandwagon of #teamcomposttea, applying a compost mulch layer and raking it into your soil is the better alternative.
Frequently Asked Questions about Compost Tea
Compost tea should be used in moderation on plants to prevent runoff and causing water pollution. Despite being an organic mixture, it can still be harmful to the environment in excess due to its high level of nutrients. Ensure to only use it once a week on ornamental plants.
Compost tea is not dangerous to the plant when given in excess. However, it may cause detrimental effects to the environment during runoffs, leading to water pollution. Plants won’t necessarily exhibit problems when given frequent doses of the liquid. Apply it infrequently to boost its growth once in a while.
Compost tea doesn’t necessarily need diluting prior to applying to plants. However, if it is ‘leachate’, i.e., the by-product fluid produced from a compost pile, it’s best to dilute it before use. It is far more potent on its own than compost tea steeped in water overnight.
As a general rule, it is best to avoid ingredients that are also not allowed for composting when making compost tea, such as:
Dairy and meat products
Black walnut tree by-products
Colored or glossy papers
Charcoal or coal ash
Herbicide/pesticide-treated plant matter
If you’d like to know more about composting, this article details everything you need to know about the process.
It’s unnecessary to add nutrients to non-aerated/non-aerobic compost tea. However, it is one of the crucial components in making aerated/aerobic compost tea. People commonly use molasses to ‘feed’ the microbes during the brewing process. But it’s important to note that this particular tea has yet to be proven beneficial for plants.
After 24 hours of steeping or ‘brewing’, compost tea is ready to be used on plants for a quick pick-me-up. It’s often best to apply it immediately once it’s done. However, this also means you should only make a moderate amount each time to prevent wastage. It’s not advisable to store compost tea as it will only stink up after a while.
It is inadvisable to use incomplete compost for making compost tea because it hasn’t sufficiently broken down and may contain harmful pathogens. Always use fully decomposed compost that looks and smells like crumbly earth. If it has a foul odor, it highly likely contains bad bacteria that will stunt your plants’ development.
All in all, compost tea only lasts for a short time. Even so, you don’t necessarily have to use it if your plant is already doing well. But if you’d like to give it a go, the non-aerated type is your best bet. Happy planting!
- Compost Tea- Miracle Product or Snake Oil?: University of Illinois Extension. (n.d.). Extension.illinois.edu. Retrieved September 28, 2022, from https://extension.illinois.edu/blogs/good-growing/2019-08-14-compost-tea-miracle-product-or-snake-oil
- Chalker-Scott, L. (n.d.). Retrieved September 28, 2022, from https://s3.wp.wsu.edu/uploads/sites/403/2015/03/compost-tea.pdf
- Chalker-Scott, L. (n.d.). The Myth of Compost Tea Revisited. Retrieved September 28, 2022, from https://s3.wp.wsu.edu/uploads/sites/403/2015/03/compost-tea-2.pdf
- Chalker-Scott, L. (n.d.). The Myth of Compost Tea, Episode III. Retrieved September 28, 2022, from https://s3.wp.wsu.edu/uploads/sites/403/2015/03/compost-tea-3.pdf
- Joe, V., Rock, C., & Mclain, J. (2017). Compost Tea 101: What Every Organic Gardener Should Know. https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1739-2017.pdf
- HS587/MV054: Comfrey—Symphytum peregrinum L. (n.d.). Edis.ifas.ufl.edu. Retrieved October 6, 2022, from https://edis.ifas.ufl.edu/publication/MV054