Everything you should know about Composting Ashes

When you live in a cold place equipped with a fireplace, you are bound to have ashes. And If you are someone interested in composting (Like Me!), you often wondered about using ashes in compost. I decided to go deep and learned everything you need to know about composting ashes. 

Can you compost ashes? It would be best if you only composted untreated wood ashes. Coal ash, charcoal ash, and treated wood ash contain harmful chemicals and should not be added to compost. These can harm the plants and enter your food if you are using compost in food plants

Composting ashes is a little different from other materials. There are several things that you should keep in mind when using them. People often feel confused about various aspects of using ashes. Here we have analyzed these aspects and compiled everything you should know about composting ashes.

How to compost ashes

Ashes can be an excellent addition to your compost if appropriately used. Here are a few things that will help you utilize ash better

  • Wood ash contains calcium that can raise the ph of soil (Make it more alkaline). It can be an excellent substitute for lime for balancing highly acidic soil. Before using ash, you should check if your soil is not already alkaline. Adding ash to alkaline soils can upset the ph of the soil.
  • It would help if you always started with adding a small number of ashes. Adding too much can be bad for the compost.
  • A good rule of thumb is to ensure that the percentage of ashes in compost remains below 5%
  • Please make sure that ashes have adequately cooled before you use them. It sounds obvious, but I learned it the hard way!
  • Wear gloves, mask, and eye protection while handling ashes. This might sound like overkill, but it can protect you from serious irritations.
  • You should always scatter ashes instead of piling. This helps in equal distribution of minerals. 
  • It would be best if you turned the pile every time to make new additions.
  • If you have a hot pile, you can add it every month.
  • If the pile is cold, add ashes during fall or late summer. This gives it enough time to break down.
  • The nutrients in ash are water-soluble, so you need to protect it from the rain.

Types of ashes you can Compost

Not all ashes are created equal when we are talking about composting. Some are good for your compost, while others can ruin it. Let’s analyze different types of ashes. 

Type Of Ash Can You Compost  it
Untreated Wood Ash
Charcoal Ash
Coal Ash
Ash From Trash Fires
Ashes From Straw 
  •  Untreated wood ash: Wood ash contains a good amount of calcium and potassium. It       also contains magnesium, phosphorous, copper, and zinc. These can help in adding     essential minerals to the soil and balancing the acidity. Untreated and unpainted wood is mostly free from toxic compounds. This can be a      great addition to your compost (In small Quantity!).
  • Charcoal Ash – Charcoal used in barbecue contains additives to make It burn better. These additives are not optimal for compost. They can even add toxicity to the pile.
  • Coal Ash – Various studies have shown that coal contains many harmful chemicals. These chemicals include mercury, cadmium, lead, aluminum, etc. NRDC (Natural Resources Defense Council) even termed it Hazardous. A study by Nicholas school of the environment found that spreading coal ash can cause the contamination of carcinogenic chemicals. So it would be best if you avoided it. In case you are wondering, what to do with it? Recycle it!
  • Paper Ash – Paper Ash produced from burning regular paper should not be toxic and slightly raise the compost’s ph. It should be noted that glossy paper, incense paper, and other variants are treated with plastics and various chemicals. These can contain harmful chemicals and should be avoided.
  • Ash From Trash Fires: Trash can contain all sorts of things like plastics, pathogens, and other dangerous substances. Ash from a trash fire can look like regular ash, but it is filled with harmful substances that can ruin your plants. You should never add it to your compost
  • Ashes from Straw: These should be free from harmful chemicals (Unless the straw is grown using heavy amounts of pesticides and fertilizers). Ashes from a straw can be used similarly to wood ash.

Benefits of Composting Ashes

If appropriately used, Ashes can be beneficial for your compost. Here are some advantages of using ashes

  • Source of Potassium – Potassium is an essential nutrient for plants. It helps regulate water in plant cells, food transportation, and the synthesis of starch and sugar. If plants remain deficient in potassium, they are vulnerable to pests, disease, droughts, and floods.
  • A lime Substitute – lime is used to reduce acidity in the soil. Several acidic soils make it harder to grow anything. Lime is alkaline in nature and lowers the ph. Wood Ash works similarly and can very well be used in place of lime. You should note that the alkalinity of ash depends on the source. It is best to access this in advance to prevent over addition.
  • Reduces Pest Activity – Wood ash has been known to get rid of common garden pests. Many farmers add it to turnips to get rid of turnip flies. The pest repellent properties are, however, reduced if water is added to it.
  • Suitable For Compost Microorganisms – A 2010 study published in Applied Soil Ecology explored the impact of wood ash on the compost. They experimented with different percentages of wood ash. The study found that a moderate dose of wood ash is excellent for soil microbiota.
  • Improves Composting Process – A 2008 Study published in Agriculture, Ecosystems & Environment monitored various aspects of composting under different percentages of wood compost added to it. The study concluded that a moderate amount of wood ash improves the overall quality on=f the compost.
  • Speed Up The Process – One 2011 study published in Bioresource Technology found a relation between low Ph and delay in the early rise of temperature in composting process (Temperature rise is required for efficient composting). The study established that 4-8% of wood ash is sufficient for effective composting and produces a good product

Some things to watch out for

There are a few things that you should be cautious of while using the wood ash.

  • You should not mix the wood ash with nitrogen fertilizer. It releases ammonia gas in these situations.
  • Avoid using it on windy days. The ashes can quickly spread and get into your eyes.
  • Soils with a pH of less than 5.5 can benefit from adding wood ash. Once the pH reaches around 6.5, more ash should not be added.
  • Avoid adding it to plants that thrive in acidic soils like blueberries, azaleas, etc.
  • Perform soil pH test at regular intervals. It will help you determine proper doses of wood ash.

Final Thoughts

When adding ash to your compost, it all about analyzing the source. Natural sources free from toxic chemicals are generally acceptable to use. Well-planned use of ash can be a boon for your compost and your plants. Try not to overdo it, though. Too much of anything is bad


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