Answer: Wood Ash In Compost – Good Or Bad

Pinterest Hidden Image

Wood Ash in Compost? Composting is a lot like Japanese recycling – There are many rules on what can or cannot be composted and many ways to sort the compostable material to get the best results.

Unfortunately, getting started in composting can be just as daunting as moving to Japan and getting a copy of your local recycling chart. Still, once you get going, it becomes second nature.

Wood ash in CompostPin

One of the best examples of this is wood ash. Depending on who you talk to, wood ash can be a good composting material or a terrible one, but the reality is a little more complicated.

Read on to learn about wood ash and when it can or cannot be composted.

Wood Ash in Compost: Good or Bad?

The answer to this question is… yes!



Before we show you how to compost with wood ash, we must review the rules.

Warning: Not All Wood Ash is Created Equal!

This is why some people swear by wood ash in composting while others swear at it.

The simple truth is that some ash sources contain contaminants that might harm your garden.

As a general rule, you should NEVER use ash from coal fires, treated wood, store-bought charcoal, or trash fires.

Also, remember that wood ash from a firepit or barbecue grill is only safe if you don’t use a chemical such as lighter fluid to start or encourage the fire.

However, untreated wood, homemade charcoal, and other types of pure wood ash are all quite acceptable.

In fact, if you harvest your wood for a fireplace or fire pit, these are both perfect for the compost pile.

Likewise, suppose you use sawdust from untreated wood (a surprisingly useful byproduct of having a workshop) for smoking meat and fish.

In that case, you can recycle the ash from your smoker and fireplace ashes for use in the compost pile, even if there are some drippings from the meat.

Ash created from burning paper products (that don’t contain chemicals is fine for use but will have fewer nutrients than unprocessed wood pulp.

Did You Know? Wood ash from burning cardboard can contain harmful chemicals, but composting cardboard directly (after sorting out which cardboard items can be used from those that cannot) doesn’t have this problem – so only burn the cardboard. You can’t compost and discard the ashes.

The Benefits of Wood Ash In Compost

Wood ash is a veritable smorgasbord of important macro and micronutrients.

It contains high levels of potassium and calcium, which are important for healthy, strong plant growth.

There’s also a decent amount of copper, magnesium, phosphorus, and zinc. Apply wood ash in small amounts to the compost heap where, once mixed in, it will blend readily with other materials.  

The high quantity of calcium makes wood ash an excellent substitute for lime, making it a perfect amendment for soil with a highly acidic pH of 6.0 or below.

Another great benefit to adding wood ash to your compost is that it’s considered a brown material. 

When sprinkled onto each layer, the wood ash aids in breaking down materials, speeding up the composting process.

It also helps reduce the smell of rot caused early on by the green materials, which can help reduce the number of unwanted insects attracted to your pile.

Too Much Of A Good Thing…

And here is another point why many are wary of using wood ash.

The high calcium makes wood ash an alkaline substance, which can do more harm than good if you use too much.

 As a reminder, browns include carbon-rich materials such as straw, hay, and dried leaves, while greens are more nitrogen-heavy items such as kitchen scraps and fresh grass clippings. 

As a result, you should never have your compost pile be more than 5% percent wood ash.

In addition to improving soil health, adding wood ash compost around plants may be beneficial in repelling some types of insect pests, like slugs and snails. 

Composting ashes can add to the richness of your garden soil as well as being a convenient and eco-friendly way of disposing of your fireplace or campfire ashes. 

Why Is Composting Better Than Direct Application?

It’s not uncommon for people to sprinkle wood ash directly on their garden soil, but this poses some huge risks that composted ash avoids.

First of all, wood ash reacts to nitrogen, which can result in the release of dangerous ammonia gas.

This reaction is far more controlled in a compost pile, which can greatly reduce any risk of inhaling the fumes.

However, when directly applied to soil treated with a nitrogen-rich fertilizer, the resulting gas can pose a major health risk to anyone not wearing proper protection.

Another major problem is the pH level of your soil.

When applied directly onto the soil, wood ash can significantly raise the soil’s pH.

This can be good for solids with a toxic pH of 5.5 or below, as very few plants will survive in such acidic soil.

However, great care must be taken when applying to acidic soil (6.0 to 6.5 pH) to avoid making the soil alkaline.

The most wood ash you should add directly to soils in the acidic pH range is 20 points per 100 square feet in the spring.

For accent plants like coral bark maple, paperbush (Edgeworthia chrysantha), and thread leaf yucca, look on the label for the mature width.

This must be worked into the soil to a depth of 6” inches to avoid harming your plants.

But properly mixing wood ash into the compost pile eliminates any risk.

This is since many of the other components in your compost pile add acidity, which will balance out the alkaline effects of wood ash.

In many cases, this can even make wood ash safe for use around acid-loving plants such as azaleas and blueberries.

Finally, wood ash contains mineral salts that can be harmful to your plants if applied directly.

However, when mixed into the compost pile, these salts are slowly leeched away by the decomposition process, making the ash safer for use around more sensitive plants.

When mixed with other components in the compost heap, the resulting alkaline compost can be used as a mulch around most ornamental plants and vegetables unless, like raspberries, rhododendrons, and roses, they require acidic soil. 

Fruit, too, performs best in slightly acid soil, so wood ashes are unsuited for use in the fruit garden. 

How To Use Wood Ash In Compost?

Wood ash must be applied only to a fresh compost pile, as waiting for the pile to start breaking down may cause the pile’s pH to rise too far. 

Wood ashes are safe to use in compost. This is the best type of ash to add to a compost bin. 

Likewise, you’ll want the ash to be fully cooled before adding it. Never mix ashes with nitrogen fertilizer. It can cause a reaction that releases ammonia gas. 

Always wear eye protection, a face mask, and gloves when handling wood ashes. 

As you create each layer of the compost pile, sprinkle the wood ash into your brown layers. It helps make compost more versatile for soil amendment. Ashes are also very alkaline and help modify the pH values of compost.  

To counteract this, it’s a good idea to add several layers of ash as you build up your compost heap.

A good rule of thumb is to add ⅛” an inch of wood ash to a 9” inch of brown layer, then add 3” inches of green layer on top of the ash, continuing this process until your pile has achieved the desired height or amount of layers.

When turning the compost, it’s possible to add more wood ash, but only if you add a full brown layer.

Otherwise, it could harm the composting process.

JOIN Our FREE Plant Care Newsletter 

By entering your email address you agree to receive a daily email newsletter from Plant Care Today. We'll respect your privacy and unsubscribe at any time.