Baking Soda in the Garden: Is it Really Harmless?

Baking soda is recommended for all sorts of garden uses including sweetening tomatoes and boosting plant growth but much of this advice is rooted in folklore not science. Let’s look at what baking soda is and if we should be using it on plants.

If you’re interested in misleading tips about using kitchen items in the garden, see popular garden myths we’ve all fallen for here.

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Using Baking Soda in the Garden

Have you seen baking soda recommended for things like “sweetening” tomatoes, pest control, or boosting plant growth?

Just about everything we can find in our kitchen cupboards is included in the plethora of homemade remedies gardeners share.

We’ve seen this with Epsom salt, dish soap, table salt, vinegar, milk, and more.

And who doesn’t love a simple household hack? I know I love them—if they work and cause no harm.

Some remedies start with a grain of truth and quickly morph into the solution for everything.

And, once someone is convinced their anecdotal evidence is reliable, no amount of reason or facts seems to help, even if the thing is truly useless or harmful.

A common belief is if something is readily available and used in the kitchen, it must somehow also be safe, “natural,” or good for garden uses as well. Nope!

A lie gets halfway around the world before truth puts on its boots.

It would be impossible to fact-check all of the claims made about baking soda—there are too many. But, by drawing on what we already know about both baking soda and how plants grow, we can separate the plausible from the far-fetched and gain an understanding of any potential benefits.

“Amazing” Uses For Baking Soda

You have probably seen a number of recommended uses for baking soda in the garden.

If you search Google for baking soda and garden, you’ll see results like this:

• 3 Ways to Use Baking Soda in the Garden
• 7 Amazing Ways To Use Baking Soda In The Garden
• 20 Great Ways to Use Baking Soda in The Garden
• 30 Ways To Use Natural Baking Soda In The Garden

Baking Soda as a Fungicide

For more than 80 years there have been claims about using baking soda for garden-related problems and boosting plant growth.

Let’s start with a popular one that at least has some credibility: baking soda as a fungicide.

As far back as the 1930s, laboratory tests showed baking soda can raise the pH level on the surface of the plant, making it less hospitable to fungi. By the 1990s we learned that it’s even more effective when mixed with oil to help it stick to plant surfaces. The mixture doesn’t kill the fungi but could stop it from spreading by preventing fungal spore germination.

We have to emphasize that this was laboratory studies under controlled conditions—something quite different than your garden or mine. You can read more about dealing with powdery mildew here.

Subsequently, it was discovered that potassium bicarbonate (KHCO3) is a better option than sodium bicarbonate (baking soda). It is used in organic farming—but that’s not what we have in our kitchen cupboards.

With baking soda, we’re talking about maybe stopping the spread of certain fungi on a plant surface, not eliminating it all together.

If you look at the baking soda folklore recipes for fungicides, they make it sound like you just spray it on your plants and, poof, problem solved.

But no. At best, in some applications, the fungi may be stalled, but there’s also a catch.

Baking soda contains sodium—something we do not need more of in our ecosystems. Yes, sodium is naturally present in soil but rarely in short supply. By combining baking soda with water, we’re releasing additional sodium which is both damaging to plant tissues and harmful to waterways.

But it’s just a small amount!

Now imagine how many hundreds of thousands or millions of home gardeners use these remedies.

That adds up to a lot of potential damage with few or no results to show for it.

Instead of throwing the kitchen cupboard at a garden problem, we’ll do better to learn the cause and research any proven solutions that do no additional harm.

Or, accept that not every garden problem warrants action.

Frequently Asked Questions

Here are answers to commonly asked questions about using baking soda in the garden.

Will my tomatoes be sweeter if I add baking soda to the soil?

No, baking soda does not sweeten tomatoes. This idea may have come from the fact that because baking soda is alkaline (pH 8), perhaps it somewhat neutralizes soil acidity and in turn decreases the acidity of tomato fruit—and that would somehow provide a sweeter taste? Kinda, sorta, maybe?

But, this is not how it works. Certain varieties of tomatoes like sun golds are naturally sweeter than others and that sweetness comes from other factors, not the application of an alkaline substance to the soil or potting mix.

Is baking soda a good fungicide for plants?

No, baking soda is not recommended as a fungicide due to its high sodium content which can damage plants and water.

Is baking soda a good insecticide?

No, baking soda is not a good insecticide. Some homemade concoctions suggest mixing baking soda with cooking or horticultural oils and spraying them on pests. It is possible that the alkalinity of the baking soda will injure the insect and the oil may smother it, but it’s an imprecise application that can cause other harm. There are better options.

Can I use baking soda to balance my soil pH?

No, baking soda is not recommended for adjusting soil pH levels. The process of altering soil pH levels is a monumental task and, at best, managed—but not permanently changed—with the ongoing application of specific agents. What you use and how often reapplication is needed will depend on your specific soil conditions. The list of commonly used amendments does not include baking soda. In most instances it is probably wiser to grow plants that suit your natural conditions or grow in containers and raised beds where you have more control over the soil.

Does baking soda kill weeds?

Baking soda is not recommended for treating weeds. While you might be able to smother a weed by piling it (or anything else) on, baking soda does not have any special properties that suppress weeds or other plants. Yes, the sodium could cause some damage but many weeds do not usually give up until their roots are removed or killed. And sodium moves easily in the soil and doesn’t know which plants you consider to be weeds.

Does baking soda improve soil? Is it a fertilizer?

No, baking soda (sodium bicarbonate) does not improve soil. Soils are rarely deficient in sodium. This means excess either builds up in the soil, which is harmful to plants, or washes away, which is harmful to waterways.

While it would be great if more of these homemade solutions worked, in practice they can be wasteful and potentially do harm.

As gardeners, are job is not just to react to a problem at hand, but to consider the totality of our actions including the impact on the environment to decide what, if anything, we should do.

Resources

Read More

• Is Cinnamon a Natural Fungicide?
• Powdery Mildew in Home Gardens (What to Do)
• Damping Off Disease: How to Deal With This Seed Starting Problem

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~Melissa the Empress of Dirt ♛