Should You Use Baking Soda in Your Garden?

Updated: Sep. 15, 2023

Spoiler alert: Baking soda is great for some things, but not necessarily in the garden. Here are common baking soda myths explained and debunked.

Like castor oil and apple cider vinegar, baking soda is one of those old-school kitchen pantry staples celebrated as a cure-all for everything from health problems to school science projects. Gardeners often tout it as a safe and healthy way to prevent common gardening headaches like pests and diseases.

But is this just another gardening hack that’s too good to be true?

“Like most things, the answer is, it depends,” says Em Shipman, executive director of KidsGardening.org. “Overall, in a pinch, there are certainly some uses for baking soda, and when applied correctly, it can be effective.

“However, it should come with a warning. In the same way it can be used to kill insect pests and burn away crabgrass and unwanted weeds, it can also harm beneficial insects that keep pests in check and burn landscape plants if applied incorrectly.”

What Is Baking Soda and How Does It Affect Gardens?

Baking soda, or sodium bicarbonate, is a salt that, when added to water, separates into sodium and bicarbonate ions. Sodium is a micronutrient that many plants need, but only in small doses, so too much can do more harm than good. Baking soda also has a pH of about 8.3 when mixed with water, which is too high for most plants.

Is It Okay To Use Baking Soda To Kill Weeds?

Technically, yes. But practically speaking, it’s not ideal.

Because high concentrations of sodium are toxic to plants, if you dump a bunch of dry baking soda onto a small plant, it will probably die. Also, because sodium is soluble, it’s likely to hurt or kill nearby plants that you didn’t want to harm.

“If you have some weeds in the cracks of a sidewalk or walkway that you’re looking to kill with less-harmful chemicals, baking soda can be a useful solution, especially when the weeds are small,” says Shipman. “But for those in your beds, it’s smarter to just pull them by hand.”

Can Baking Soda Cure or Prevent Fungal Disease?

Yes and no. The internet is full of recipes for homemade pest and plant disease control.

However, Shipman says, “There is little scientific evidence to confirm or deny the efficacy of these formulas and their ability to cure or prevent fungal diseases like powdery mildew. A baking soda spray might work in a pinch and can slow the spread of some fungal diseases. However, it will not cure already existing damage, and there’s a chance it will burn leaves.”

Instead, try neem oil, also considered safe to use around pets and children.

Can Baking Soda Kill Insect Pests?

Yes. But most DIY baking soda insecticide recipes call for a blend of water, baking soda and either soap or horticultural oil, which functions as a surfactant to help the solution cling to the leaves.

“It’s likely that the soap or horticultural oil is doing most of the work to deter or control the insect, rather than the baking soda,” says Shipman.

Does Baking Soda Freshen Compost Piles?

Possibly, but there are better alternatives.

Just like in the refrigerator, baking soda can absorb or neutralize acidic gases and rancid smells in compost, but it needs to be applied directly to the pile and mixed in. In most cases, unpleasant compost odors are caused by an imbalance of ingredients in the compost, such as too much nitrogen-rich material.

“Adding carbon-rich materials, such as dead leaves or straw, is a better alternative,” Shipman says, “because this will absorb the liquids that cause most unpleasant odors, provide the proper environment for the microbes doing the composting, stop the smell, and produce high-quality finished compost.”

Does Baking Soda Make Good Fertilizer?

Nope, that’s a myth. While sodium is a micronutrient needed by many plants, they only require small amounts. Therefore, adding baking soda to the soil will likely cause an excess of sodium and do more harm than good.

“A better way to provide plants with the array of nutrients they need is by adding compost or other natural fertilizers,” says Shipman.

Does Baking Soda Make Tomatoes Sweeter?

Probably not. Some vegetable gardeners claim adding baking soda to the soil around tomato plants produces sweeter fruit. The logic: Because baking soda is alkaline, it reduces acidity in the soil. Less acidic soil means less acid in the plants and therefore sweeter tomatoes.

“Unfortunately, there is no clear evidence for this,” says Shipman. “The sweetness of tomatoes is due to many factors, the most important being the varying chemical composition of different types of tomatoes. It is unlikely that baking soda would have a significant effect, and it may cause problems with excess soil sodium.”