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Potassium Bicarbonate: Effective Fungicide for Gardens and Orchards

Discover the world of potassium bicarbonate, an approved organic product for fighting fungal diseases in vegetables and fruit trees. Learn how it works and how to use it effectively.

by BioGrow

Potassium bicarbonate is widely used in organic farming as a fungicide. This potassium salt is also called potassium hydrogen carbonate. Thanks to its particular action on the blade of the leaves, it manages to protect the plants from agents fungal pathogens, be they vegetables, vine plants or fruit trees. It appears as a white powder, very similar to sodium bicarbonate, but with some differences, which make it preferable to the latter for professional use. Potassium bicarbonate is also used in oenology, as an acidity corrector in the wine production process.

We therefore know this product, its properties and practical uses in our organic crops.

What Is Potassium Bicarbonate?

Potassium bicarbonate
Potassium bicarbonate, also known as potassium hydrogen carbonate, is a salt of carbonic acid. It is obtained through a chemical reaction involving potassium carbonate, carbon dioxide, and water. Here is its chemical formula: K2CO3 + CO2 + H2O → 2KHCO3.
In the market, it is available as a pure, fine white crystalline powder, typically at 99% purity. It is highly soluble in water, with 33.2g dissolving in 100g of water at 20°C. Once dissolved, potassium bicarbonate dissociates into potassium and bicarbonate ions, with a pH value of 8.54 for a 1% solution. The pH is strongly alkaline. It is not irritating to the eyes or skin, making it safe for use. Studies have not indicated any mutagenic, carcinogenic, or neurotoxic risks.

Potassium Bicarbonate in Organic Agriculture

Potassium bicarbonate is among the products permitted in organic agriculture and can be used without the need for a phytosanitary license. At the European level, its use is included in Annex I of Directive 91/414/EEC for fungicidal purposes and is authorized in organic farming by European Commission Regulation No. 404/2008.

Antifungal Properties

Let’s delve into how potassium bicarbonate acts on plants and its antifungal action. The mechanism is quite simple: upon contact with the leaf surface, potassium hydrogen carbonate immediately raises the pH value to at least 6.4. This creates an inhospitable environment for fungal growth. Its action on the pathogen is rapid and direct, altering osmotic pressure and creating an alkaline environment. This inhibits mycelium growth, causing spore collapse and dehydration of the fungal hyphae. Thanks to its immediate action, this type of bicarbonate can even be used as a curative product, especially when plant diseases are in their early stages. However, it is more effective preventively and should be used when conditions are favorable for the pathogen. It can be used as a tonic to enhance the natural defenses of plants.

Which Diseases Does Potassium Bicarbonate Treat?

Cryptogamic diseases are a real scourge for farmers, both hobbyists and professionals. Potassium bicarbonate is effective in preventing the most common fungal diseases in vegetables and fruit trees. These include:

  • Downy mildew of grapes and tomatoes;
  • Powdery mildew in grapes and cucurbits (pumpkin, zucchini, cucumber etc);
  • Botrytis or gray mold on grapes and other crops;
  • Leaf curl of medlar and apple;
  • Monilinia or brown rot in stone fruits (cherry, peach, apricot, plum etc);
  • Peach leaf blister.

How to Use Potassium Bicarbonate

Potassium bicarbonate should be dissolved in water and sprayed on plant foliage. But what product should you use, and at what dosage? The answer depends on the type of commercial formulation you have purchased. This type of bicarbonate is available both in agricultural supply stores and in winemaking shops. (Pure powder available here) is used in winemaking. For agriculture, there are specific formulations with an 85% concentration. With this second type of product, you will have precise dosage instructions on the label. If you choose to use pure powder, it is advisable not to exceed a concentration of 0.5%, which is 500g of potassium hydrogen carbonate per 100 l of water.


The potassium bicarbonate solution should always be used in the evening. This increases the persistence of moisture on plant foliage. Never apply the treatment in full sun or at temperatures above 35°C. Treatments should be repeated after rainfall, as potassium hydrogen carbonate easily dilutes, losing its protective effect. Typically, preventive interventions are done in spring and autumn when fungal diseases are prevalent.

Precautions for Use

Be careful not to exceed the number of treatments. Potassium bicarbonate, when it leaches into the soil, alters the soil pH, making it more alkaline. This can be positive for most crops, so it can also be used as a corrective for acidic soils. However, on already alkaline soil, one must be careful not to overly alkalize, as this can hinder the absorption of other nutrients such as calcium. It can also be used alternately with conventional copper-based products for more effective defense in both vegetable gardens and orchards.

Similarities and Differences with Baking Soda

As many already know, baking soda is also used as a fungicide for plants, especially in domestic settings. Its action is the same as that of potassium bicarbonate, altering the pH of the leaf surface and preventing fungal growth. However, if used too frequently and at incorrect dosages, it risks damaging leaves, causing burns. Additionally, it releases sodium into the soil, which can become a long-term problem. Nevertheless, it is available in supermarkets, is cost-effective, and is a common household item. It also has excellent efficacy. Potassium hydrogen carbonate, on the other hand, is less harsh on leaves and acts more quickly.

Potassium Bicarbonate in Winemaking

Potassium bicarbonate (E501) is used in winemaking as a deacidifying agent. It can be added to the must or directly to the wine. It reacts with tartaric acid, producing potassium bitartrate. After cold stabilization, this compound will precipitate, further reducing total acidity. Essentially, it softens the wine, often necessary in artisanal winemaking. The maximum deacidification allowed in wines by law is 0.65 g/L expressed as sulfuric acid (1 g/L expressed as tartaric acid), which corresponds to a dosage of potassium hydrogen carbonate of 1.3 g/L. It is used by dissolving it in a portion of the must or wine, which will then be added to the final volume. When used before final bottling, it’s advisable to wait at least 1 month before bottling. Enological potassium bicarbonate can be found here.

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