Composting is an excellent method to recycle all sorts of organic materials. From food scraps to grass clippings to newsprint, you can throw it all into your compost heap. You can even add sawdust and ash to your pile. But you should consider the type of shavings or ashes you are adding. These materials are not created equally. For example, you might have ash left from your coal-burning stove. Can you put coal ash in compost?
No, coal ash should not be added to your compost. Coal ash can contain chemicals or metals that can compromise your compost and eventually damage your plants or garden.
Chemicals and metals in compost sound scary to us. We researched the topic in depth. Keep reading as we answer some questions and help you understand why you should keep this type of ash out of the compost heap.
Harmful Elements In Coal Ash
Coal ash contains chemicals like arsenic. And the ash can also contain heavy metals like aluminum, lead, mercury, and cadmium. Too much exposure to these elements can be toxic. And the levels of toxicity can vary. The amount of coal ash you produce at home is probably fine; you’re not running a power plant. But, ongoing exposure to coal ash can cause health problems.
Some view the coal industry as dirty. Others find coal to be an excellent resource. Ash from coal is a controversial topic, especially when it comes to soil. Studies such as the one from Duke’s Nicholas School of the Environment states that spreading ash on soil raises the risk of contaminating the water supply with carcinogenic elements.
Now we realize that coal plants have a massive amount of ash to deal with and dispose of, and you probably don’t. But keep in mind, your compost should be free of anything harmful. All the ingredients that you put into your compost should be organic. Coal ash is a byproduct that has the potential to be damaging.
Small amounts of ash might be okay to add to your compost bin, but why take the risk?
How Much Coal Ash Can You Put In Compost?
Since coal ash can contain chemical residue, we don’t recommend that you put this type of ash into your compost. But, according to an article in Scientific American, small amounts of fly ash, a subcategory of coal ash, mixed with compost can help plants grow and increase crop yield.
If you decide to add some coal ash into your pile, make sure that your heap is well balanced with other organic items. You should also be in the habit of regularly turning over your compost or using a tumbler to mix it. For more details on tumblers, check out our post How Long Does it Take to Compost in a Tumbler.
Should You Be Going Out Of Your Way To Add Coal Ash?
There is no need for you to add coal ash to your composting pile. The ash you create is somewhat different from the ash that power plants produce, but there isn’t enough evidence to support ash will help a compost. Coal ash might harm your pile.
If you want to use the ash you have, add small amounts to your compost bin or heap. Once it’s cured, add the cured material to your soil and test it. If the soil is well balanced for your plant’s needs, then you are good to go.
You can also try using ash with certain plants or trees in your yard. You should test your soil’s pH level as well as other nutrient levels like phosphorus and potassium.
The compost you create is an amendment to the soil you use. So knowing what the soil is lacking will help you decide if coal ash is of any help.
Can You Put Coal Ash Directly On Garden Plants?
You can put coal ashes on garden plants but do so with caution. Coal ash might increase the pH of your soil. It’s best to have your soil tested so that you have a better understanding of what it needs.
In our research, we’ve encountered many folks who claim that ashes help them grow better plants and gardens. One reason might be that ashes can impact a soil’s pH. Tomatoes or potatoes, for example, benefit from soil that has a high pH. Whereas blueberries would not benefit from coal ash as they need more acidic soil.
If you need to amend the soil for your garden plants, coal ash might help break up clay soil and improve drainage. If you have clay soil that is challenging you, read our post How To Improve Clay Soil For Lawns.
And, keep in mind that coal ash contains heavy metals. The amount of metal in your coal ash is unknown and might be so small it doesn’t matter. Many people use coal ash in their gardens without hesitation. They stand by the benefits of coal ash with their thriving gardens.
At the same time, though, other people are uncomfortable not knowing if the coal ash might be toxic. If you are worried, stick to the safer side and don’t add coal ash to your garden.
What Is Coal Ash Used For?
Coal ash is a catchall term to describe what’s left after coal has been burned. The residual ash is organized into three subcategories: Fly Ash, Bottom Ash, and Boiler Slag. The coal industry tries to repurpose each of these subcategories of ash.
Fly Ash
Fly ash is light and flies up exhaust stacks. The fine particles of ash float into a stack. The ash is commonly added to construction materials like cement. The use of fly ash is a hot topic. Using it in building products is thought to be safe. But it’s still a byproduct of coal and contains heavy metals.
Bottom Ash
Bottom ash is coarse, dense and hard. This ash is heavier than fly ash and settles on the bottom of the boiler. Bottom ash is also recycled into cement. Other uses include a road base or filler material for roads. Some states spread the ash on snowy or icy roads. The coal ash at your home will be more like bottom ash.
Boiler Slag
Boiler slag is molten bottom ash. Like fly ash and bottom ash, it can be used in cement. And, this type of ash can also be used on icy roads to create friction. Boiler slag is also used as roofing shingle granules.
Even though coal ash has many uses, what’s not recycled sits in landfills. And, those landfills are potentially dangerous.
Is Coal Ash Considered Hazardous Waste?
If you want to know the answer to this question, it depends on who you ask. According to The Natural Resources Defense Council (NRDC), coal ash is most definitely a hazardous waste.
The U.S. Environmental Protection Agency (EPA), on the other hand, doesn’t classify coal ash as hazardous waste.
There are events in history where coal ash sludge from the landfills it sits in have accidentally spilled into waterways or covered miles of land. These events have caused a lot of damage and put people’s health at risk.
Recycle And Reuse Ash
As we discussed in the post, coal ash can be recycled. And for some products like cement or wallboard, the result is a stronger, more durable product. And, as far as we know, the toxins are eliminated during the recycling process.
There are also successful commercial uses of recycled fly ash used to amend soil on large farms and crops.
But trying to repurpose coal ash in your compost might not be that simple. Given the risk of the many toxins from metals that can potentially leech into your soil, it might be best to pitch the coal ash into the trash.