Is Coal Ash Good for Your Garden? A Gardener Shares How to Use It for Healthier Soil

• Coal ash can be added to a garden to raise pH levels for soil that is too acidic or alkaline-loving plants.
• It can have low amounts of harmless trace metals that can accumulate over time, so be sure to test for metals on occasion.
• Other waste materials—like wood ash, compost, coffee grounds, and eggshells—can be added to gardens for additional benefits.

There are so many ways to enhance and improve our soil, and it’s growing increasingly clear just how important it is to have a well-fertilized garden. With this in mind, we’re always on the lookout for potential ways to enhance our soil and add more nutrients for our plants.

Lately, we’ve been hearing more and more about using coal ash in our gardens, and were curious to know more. We checked in with a pro gardener and find out if this coal-burning byproduct is actually good for plants.

Is Coal Ash Good for Plants?

According to horticulturist Justin Hancock, coal ash is exactly what it sounds like—and yes, when used in the right situations, it can be good for your garden.

“Coal ash is the powdery residue left over after burning coal,” Hancock says. “Ash has been used in the garden as a fertilizer or soil amendment because it contains key nutrients needed for plant growth.”

Most homeowners collect their coal ash from charcoal stove or barbecue, and—once cooled—sprinkle it over their garden as a fertilizer alternative.

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Benefits of Using Coal Ash for Plants

The reason coal ash works well as a fertilizer supplement is because it has a high pH level, making it alkaline, or basic. As Hancock points out, this can help balance really acidic soils, but that also means it might not be as useful if your soil’s acid levels are normal or low.

“Coal ash can be good for plants that don’t require acidic soil as it provides nutrients like phosphorus and calcium,” Hancock explains, noting that if you have some on hand, sprinkling coal ash is a great way to use it.

“If you have access to coal ash, it’s easy to see why you might use it in the garden rather than throwing it away,” he says.

However, if you have plants that aren’t bothered by acidic soil there’s probably not much of a benefit to using coal ash at all over other organic soil supplements.

In order to know whether coal ash is right for your garden, Hancock says you should check your soil’s pH first. Once you understand the acidity levels, then you can decide whether or not it’s a sensible addition to your gardening routine.

Potential Problems Using Coal Ash

Because coal ash alters your soil’s pH levels, extended or heavy use could majorly impact which plants you can grow in your garden. That’s why it’s important to check your ideal plants’ acidity preferences before sprinkling coal ash over your soil.

“That could become problematic if your soil isn’t highly acidic or you’re trying to grow plants that love acidic conditions like blueberries or rhododendrons,” says Hancock. 

Along with messing with your soil’s pH levels, coal ash may also contain heavy metals like arsenic and lead. This probably goes without saying, but Hancock notes that this isn’t something you want in your garden. 

“The amounts of these heavy metals are generally pretty low, but over time they can accumulate,” he explains.

The added concern here is if you’re growing fruits, herbs, or vegetables, as these heavy metals can be absorbed by the plants.

“You may want to think twice, or at least be cognizant of the amount of coal ash you use,” says Hancock. “And test your soil regularly to see what the heavy metal content is.”

Other Organic Waste to Add to a Garden

Either along with or instead of coal ash, there are plenty of other organic wastes you can add to your garden with positive effects.

As Hancock points out, wood ash, like coal ash, is another possibility for fertilizing your garden with similar effects, and a great choice if you have a fireplace or woodstove. Hancock notes that this also tends to contain fewer heavy metals than coal ash, making it a slightly preferable option for some gardens.

Beyond ash, you can also use compost as another option for adding organic waste to your garden. In fact, Hancock says that this is his own personal preference.

“While it’s not as nutrient dense as ash, compost helps support more beneficial microorganisms, improves sandy/clay soils, and has other benefits,” he says.

If you’re interested in adding more organic waste to your garden outside of general-purpose fertilizer and compost sounds appealing, you can consider the below:

• Fruit and vegetable scraps
• Used tea bags and leftover coffee grounds
• Shredded newspaper or cardboard
• Crushed eggshells
• Garden waste, such as clippings, prunings, and fallen leaves