We write about this topic every year because, quite frankly, there’s a lot of misinformation out there on the internet about the benefits of using fireplace ashes in your garden. And since, we are entering fireplace season, this seems like a good time to review how the potential negative side effects outweigh any potential benefits associated with placing fireplace ashes in your garden.

If you poke around the internet, you’ll find articles suggesting that fireplace ashes are a great source of potassium for your garden. Potassium is one of the big three nutrients we try to manage in our gardens (nitrogen, phosphorus, and potassium). If you read our articles, you will know that nitrogen is known as a mobile nutrient while phosphorus and potassium are known as immobile nutrients. Nitrogen moves easily in the soil while phosphorus and potassium do not. Those two tend to stay in place.

Nitrogen is kind of like fuel, it gets consumed. On the other hand, levels of phosphorus and potassium do not vary much, they just need to be present at the correct levels. Since they don’t get consumed like nitrogen, we need to be careful about just adding these nutrients when we choose. Since they hang around in the soil for a long time, it would be easy for them to build up to unhealthy levels if we just keep adding without knowing whether we need these nutrients or not. You probably get tired of hearing us say this, but the only way to know your nutrient levels for sure is to get your soil tested. We have information on our website in the Lawn and Garden section under Soil on how to get a soil test (www.tulsamastergardeners.org).

But there’s a potentially bigger issue with adding fireplace ashes to your garden, it can affect your soil pH. As gardeners, we need to keep our garden soil at a mostly neutral pH of around 7.0, maybe even a little less. Why? Because the pH level of your soil affects nutrient availability. With a neutral pH, most nutrients and micro-nutrients are available to your plants. Of course there are exceptions, but for the most part, this is true. The problem with fireplace ashes is that they have a pH of around 11 or 12 which can contribute to raising your soil pH to unhealthy levels for your plants. Now, if you needed to raise your pH and you had a potassium deficiency, fireplace ashes could help, but to know that you would need to get a soil test. Adding fireplace ashes without this information is likely going to work against you in the long run.

So, our recommendation is to avoid putting fireplace ashes in your garden. In all likelihood, they won’t help and more than likely they will make growing conditions in your garden worse. In other words, just say no. Good luck!

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th Street, or by emailing us at mg@tulsamastergardeners.org. Photo: Pixabay