Leave a kilo of fresh horsetail stems in nine litres of rainwater and, within a fortnight, the liquid turns black and the leaves collapse to slime at the bottom. Diluted one part in ten, this free fungicide guards fruit trees and vegetables against powdery mildew, rust and scab, provided you spray regularly, before disease appears.
Horsetail can be harvested virtually anywhere since it is one of the most common wild plants. Fermented tea is very easy to prepare from it, and waiting time before use is short.
Finally, avoid growing it in your own garden, it is a truly invasive species that will overtake your plot unless you lock it in as if it were bamboo!
An alternative is to have it grow in a large tub. It also does great at the foot of conifer hedges, that can be locked in by pavement on either side.
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This technique is a simple two-week cold maceration: no boiling, just waiting.
An alternative recipe, instead of two-week cold maceration, is to let it macerate for only 24 hours. After this day-long maceration, boil the leaves and water together for 20 minutes. Cool and filter before use. This makes the fermented tea available for use much earlier.
Boiling, however, degrades some of the nutrients of the plant so it won’t have such a high fertilizing side-effect, but that’s a secondary consideration when treating against diseases.
Out of season, it’s hard to get fresh horsetail. You can still make this “magic potion” from dried horsetail! That way, all you need to do is dehydrate the weeds in season and then rehydrate them later on, when you need to use the plant.
Powdering helps the plant break down faster when preparing the mix, but it will also work well with whole dried plants.
Again, you’ve got two options here: you’ll get more nutrients if you ferment this material, but you can use your mix faster if you boil it. For both options, just follow the steps described above, adjusting for dried weight (use only 10% of the basic recipe).
Other than that, follow the same process!
The article gives three routes to the same spray: a slow cold maceration, a quick boil, and a version made from dried plants out of season. Choose according to how soon you need the liquid and whether you also want its fertilising side-effect.
| Method | Plant material | Waiting time before use | Nutrient value |
|---|---|---|---|
| Cold maceration (basic recipe) | 35 oz (1 kg) fresh leaves in 9 quarts rainwater | 1 to 2 weeks, stirred twice a day | Highest, keeps the fertilising side-effect |
| Short maceration then boiling | Same fresh weight, boiled 20 minutes | 24 hours, plus cooling and filtering | Reduced, some nutrients degraded |
| Dried horsetail, fermented | 3.5 oz (100 g) dried material for the same volume | 1 to 2 weeks, as for fresh leaves | Good, fermenting retains more nutrients |
| Dried horsetail, boiled | 3.5 oz (100 g) dried material, boiled | Fastest of the four | Lowest, but adequate for treating disease |
Whichever route you take, filter the liquid and keep it out of metal containers.
Fermented horsetail tea is mainly used in spring and in fall, when diseases are most certain to appear.
Mixing ratio is 10% fermented horsetail tea to 90% water.
Spray regularly to avoid all chance of disease.
Coat both leaf surfaces until they glisten, since downy mildew and rust usually colonise the undersides while powdery mildew often starts on top, so complete coverage guards against whichever pathogen turns up.
Heavy rain washes foliar sprays such as horsetail preparations off the leaves, so reapply after a downpour rather than relying on the earlier application to remain effective.
Strain the diluted tea through a fine cloth as you fill the sprayer; leftover slime from the maceration quickly blocks the nozzle.
Horsetail tea is particularly effective against:
Horsetail tea shields healthy tissue rather than curing it, so pick off and bin badly spotted leaves before you spray.
Soluble silicon absorbed by plants can stiffen cell walls and hinder fungal penetration in some crops, but horsetail’s silica is largely insoluble, so evidence that horsetail preparations deliver this protection remains limited.
It does nothing against bacterial or viral troubles such as fireblight or mosaic virus.
Fermented tea can keep for several weeks in a rather cool and dark place.
Again, choose a sealed container that is not made from metal.
Use a wood barrel or plastic jug or barrels.
Avoid iron, copper and other metal-like containers since they would react with active ingredients and render them ineffective.
Most important is to keep the fermented tea “alive”: all yeasts contained in such fermented weeds must be protected from freezing and from heat waves.
Although the base material is free, the time you put in it needn’t go to waste. You can spray leftover tea on healthy plants to give their immune system a boost, too!
Indeed, sometimes fungal diseases are present even if the plants don’t show any symptoms yet. For instance, on some Septoria host plants like tomato, incubation can last from 2 to 4 weeks before the first spots appear.
When planting flowers or preparing soil mix, moisten the soil up with fermented horsetail tea to cleanse it from damaging fungus.
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