Chopped weeds left to steep in rainwater for a week or two collapse into a black, pungent slurry; strained and diluted to a tenth strength, it sprays onto leaves and soil without scorching them. Fermented weed tea works by strengthening the plant’s own defences rather than killing pests, so it rewards those who apply it before trouble arrives.
Here are the steps to prepare them and a summary of their specific advantages and characteristics.
Take note that generally, fermented tea is best used as a preventive treatment, and often cannot treat a disease once it has contaminated a plant.
Over time, gardeners learned that most weeds would make great fermented weed tea. In effect, the basic recipe is always very similar, but certain weeds have different steps.
Different weed teas have slightly different recipes.
Although it’s possible to use almost any kind of weed to prepare nutritious weed tea, some weeds appear more often than others in traditional recipes. Each one has different properties and helps deal with different problems.
Stinging nettle weed tea – boosts the plant’s immune system, especially against different types of fungus. Aphids are repelled by it.
Rhubarb fermented tea – quick to prepare. Mostly used against insects like allium leaf-mining flies and aphids.
Garlic (decoction) – effective to prevent fungal disease. Fends off aphids, thrips, mites and ticks.
There are more, of course, such as fermented horsetail or the well-known comfrey weed tea.
Comment below to ask if a local weed that’s driving you crazy might be converted to a useful fermented weed tea!
Almost any weed can be fermented, but the ones that come up again and again in traditional recipes each have their own speciality. Use this to pick the batch that matches the trouble you expect.
| Weed tea | Main action | Pests it deters |
|---|---|---|
| Stinging nettle | Boosts the plant’s immune system, especially against fungus | Aphids |
| Rhubarb | Quick to prepare, aimed at insects | Allium leaf-mining flies, aphids |
| Garlic (decoction) | Prevents fungal disease | Aphids, thrips, mites and ticks |
Batches can also be mixed, in which case you gain the benefits of each plant used.
It’s perfectly possible to make batches of fermented weed tea by mixing material from different plants together. You’ll have the benefits of each.
Fans of the process have a continually fermenting pot or barrel somewhere in their garden where they keep adding plant material as they weed the garden.
Water – must be as close as possible to natural rainwater. Avoid tap water if possible. If you must use it, let it sit for at least an hour, at best a whole day, without a lid. Chemicals that keep it safe for drinking, like chlorine, will evaporate.
Trigger – usually enough micro-organisms are present on the leaves themselves to launch the fermentation. These are called epiphyte organisms, meaning they live on the plant without parasiting it.
Timing – you can harvest the weeds anytime, but fermentation starts fastest and nutrient conversion is highest when you follow these tips:
Put a cover on your fermenting weed tea to keep insects out and smells in. This will keep mosquitoes from multiplying and small animals from falling in.
Usually degraded plant materials are filtered out. This makes it easier for sprayers and watering cans. But you can keep them to trigger the next batch, enrich your compost or mulch needy trees with it!
The most important advantage is that this tea is “alive” as opposed to “sterile” products.
It creates and strengthens the ecosystem. Consider your plant as part of a community. Fermented teas try to build the community up and increase biodiversity. Chemicals are more single-minded about things.
| Insight | Chemical products | Fermented tea |
| Mode of action | Harms the pests | Empowers the plant |
| Effect on plant | Weakens the plant | Strengthens immunity |
| Effect on beneficial animals | Eliminates them, too | Usually not impacted |
| Effect on soil | Slowly sterilizes it | Makes it richer |
| Effect on water | Leaches to the watertable | None |
| Effect on humans | Toxic warnings when handled |
Depends on weed used, some can even be drunk |
| Repeatability | Repeat application at each new infection. |
Immunity increases, need to repeat decreases |
| Long-term effect | Pest develops resistance to treatment |
Plant develops resistance to pest |
| Battlecry | Kill them all! | Crowd the invaders out! |
There are a few disadvantages, which are mostly related to how we organize our work. Indeed, chemical products are just a click away online, or a short drive to the garden center. They’re usually immediately effective and make for faster treatment.
Plants never exist “alone” in their environment. They are surrounded by living creatures. We’re familiar with most insects and caterpillars, but there are also microscopic members in this community.
Epiphyte micro-organisms are those tiny germs, fungus, yeasts, molds and mites that live on the surface of plants. They cover leaves, stems and trunks.
Mychorrhizae are underground fungi that work with plants together to extract nutrients from decaying material and available minerals.
Fermented teas develop lots of yeasts and beneficial germs. Spraying on both leaves and soil helps. They make the plant’s work easier by:
The technical term for this is “infection antagonists”, meaning they fight infection together with the plant.
In a way, one can say “it brings out the best in all of us”, since even us humans are made more aware of the intricate beauty of nature!
In an experiment involving beneficial yeast and bacteria on tomato plants, a significant reduction in infection took place. This was conducted on Septoria fungus, a common cause of leaf spot.
Infections dropped by 20 to 80 % compared to untreated specimens. Results varied depending on the yeast and bacteria used, but every case showed an improvement against the control sample.
Whenever plants need nourishment or are under stress, fermented weed tea can help.
With this in mind, it’s worth working these natural solutions into your usual gardening routine. By and large, weed tea will work wonders for the garden, your wallet, and everybody’s health, including the planet’s!
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When preparing it, find a spot that’s a bit far off, because it sometimes releases quite a stench! Also, place a lid (not an airtight one), it’ll help lock the smell in.