Baking soda claims range from controlling powdery mildew to battling ants and slugs, killing weeds, and helping your tomato plants grow sweeter fruit.
This “natural” cure-all is, unfortunately, not able to live up to all those claims.
Before we get started, let me step up on my soapbox about the use of the word ‘natural’.
As a proponent of organic gardening and least harm, it irks me when people say natural is better, because sometimes it isn’t. Malaria, death cap mushrooms, and the flu are all natural.
Just because something is natural does not necessarily mean it is what you want in your garden. ‘Nuf said.
Baking soda as weed killer
Just dump baking soda on top of weeds and they will die! True? Yes, probably. Good idea? No, definitely. Baking soda, or sodium bicarbonate, is a type of salt. Remember reading about victors salting the fields of their enemies? This was done so that the losers couldn’t grow any food in those fields. Sprinkling handfuls of salt around your garden is never in your plants’ best interest.
Baking soda and soil pH
Baking soda is highly alkaline. You will find countless articles pointing to the use of baking soda as a way to boost flower production and improve fruit sweetness because of this increased alkalinity. This is only partially true. While improper soil pH can impact fruit and flower production, simply adding baking soda is not the solution. Low flower production can have many causes: not enough or too much sunlight, improper fertilizing, irrigation, or placement, pests or disease, or nutrient imbalances in the soil. Fruit sweetness or acidity is more often a function of irrigation levels and overall plant health, than anything else. To boost the flavor of your tomatoes and many other crops, forget the baking soda and try deficit irrigation.
If soil pH is making it difficult for your plants to absorb nutrients, you can try altering it, or you could select plants better suited to your local soil. Altering soil pH is difficult and it requires accurate testing and regular treatments. Simply sprinkling baking soda on your soil is more likely to raise the salt content to toxic levels.
Baking soda as pesticide
You have probably read that you can mix baking soda with sugar to create the perfect DIY ant poison. Supposedly, the ants take the mixture back to their colony, where they eat it and then explode. Nope. Doesn’t really happen. Think about it. From an ant’s perspective, the sugar granules are probably about the size of a tennis ball and easily discernible from the baking soda bits. Plus, I could not find a single piece of scientific research to back up the ‘exploding’ claim. As for slugs and snails, well, baking soda is a salt. Salt does terrible things to slugs and snails. Better to feed them to your chickens or just step on them and be done with it.
Baking soda as fungicide
Countless ads and articles point to baking soda as a fungicide. This is because most fungi grow best in a slightly acidic environment and baking soda has a pH of 8.4, which is more alkaline. When conditions become too alkaline, fungi stop growing. Until conditions improve, that is! Then, they take up exactly where they left off. Because of this, baking soda is considered fungistatic, and not a fungicide. Also, while baking soda’s fungistatic properties are well documented in lab situations, those results have not translated to outdoor growing conditions, such as are found in your garden.
If you can completely cover a surface with a baking soda solution, you may be able to temporarily halt the development of any resident fungi, such as those that cause black spot or powdery mildew. But, right away, problems begin to occur. First, ever-increasing amounts of baking soda are needed for the same effect. Also, being water-based, the solution needs to be replaced after every rain, and each treatment adds more salt to the soil than is healthy for plants or important soil microorganisms. You can, however, mix baking soda with horticultural oil for moderate, but inconsistent, results. Just be aware that phytotoxicity can occur. [Phytotoxicity means ‘poisonous to plants’.] When combatting powdery mildew, better results can be obtained by using potassium phosphate, potassium carbonate, sulfur, or even milk sprays.
That being said, baking soda solutions can slow the development of certain fungi on produce after it has been harvested. Commercial growers frequently treat thick-skinned produce, such as citrus, with a boiling bath of baking soda in solution to prevent fungal growths while the fruit is in storage or being shipped. This is because the fungi that cause the blue and green molds on citrus are particularly sensitive to alkalinity caused by baking soda. In fact, that’s where the whole baking soda craze got started - from a test on citrus molds conducted in the 1930s.
You may be surprised to learn that the use of a coarse organic mulch, such as arborist wood chips, provides better disease suppression than baking soda treatments. This occurs because the wood chips make life more difficult for fungal spores.
Baking soda performs wonderful tasks in the kitchen, making muffins, deodorizing the fridge, and putting out grease fires. Let’s leave it there, where it can do the most good, and not in the garden.
You can grow a surprising amount of food in your own yard. Ask me how!
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