Can you put wood ash in compost

How to Compost Wood Ashes

Up here in Vermont, the winters are long.

For me, this means months spent curled up by the wood stove with a book and a cat on my lap.

It also means the creation of a lot of ash – which always leads me back to the question of whether or not I can compost ashes.

As it turns out, the answer is yes, with a couple of crucial caveats.

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This article will explore how to use wood ashes in the compost and in your garden, and when it is appropriate to do so.

What You’ll Learn

• Benefits of Wood Ash
• Test Your Soil
• When to Compost: Timing and Moderation
• How to Compost
• Adding It Directly to the Garden

Benefits of Wood Ash

Wood ash from your fireplace contains a number of nutrients that can be very beneficial to a garden – in the right circumstances.

But never use the ash from charcoal, trash fires, or treated wood, which can contain toxic chemical residue from additives.

Wood ash contains potassium and calcium in considerable quantities, as well as lesser amounts of magnesium and phosphorus, and micronutrients such as copper and zinc.

Due to its high level of calcium, it can increase the pH of soil, making it an ideal natural substitute for lime, an amendment often used to balance soil that is too acidic.

It can be a very useful amendment where acidity is too high for growing most veggies, in a pH range of 6.0 and below.

But you’ll need to be cautious. If the soil is already neutral or alkaline, adding ashes will cause excess alkalinity and add soluble salts, ultimately doing more harm than good.

So how do you know when it makes sense to add ashes to your compost or garden?

Let’s explore.

Test Your Soil

Before adding ashes (or any other amendment, for that matter) to your garden, be sure to get your soil tested!

You can easily request a test through your local agricultural extension office.

You can buy home pH test kits or meters at your local hardware store or online, though I would recommend getting a test from your local extension office at least once.

The results of these tests are more comprehensive and they will tell you a whole lot about your soil, including information about any other nutrient deficiencies.

If you don’t have access to professional testing or a kit, it is possible to DIY a basic test of the pH with just two cups full of soil, some vinegar, and some baking soda.

Pour vinegar into the first cup. If the soil begins to fizz, it is alkaline.

Add some water to moisten the soil in the second cup, then add baking soda. Fizz this time means it is acidic.

This method is not especially accurate, and you won’t be able to determine the exact pH level of your soil this way. It is still a good idea to get a more accurate test when you are able.

In the meantime, however, this simple method should at least give you a general sense of whether the soil is acidic or alkaline.

When to Compost: Timing and Moderation

The key is to add small amounts of cooled ashes to a new or uncooked pile. Because it has such a high pH value, it is important that you don’t add too much to your compost.

According to Olivia Saunders, Extension Field Specialist in Food and Agriculture at the University of New Hampshire Extension, “it should not make up more than 5% of your compost.”

Additionally, once the compost nears maturity, the addition of ash could raise the pH too much, increasing the bioavailability of heavy metals to harmful levels.

How to Compost

Before you start, be sure to suit up with gloves, eye protection, and a mask to avoid any potential irritation to the skin, eyes, or lungs. Also, ensure that the ashes have completely cooled before handling them.

Sprinkle the ash onto your compost pile along with the appropriate ratio of brown and green material.

What does this mean? Add about a quarter inch for each 18-inch section of browns and for every six inches of greens. Be sure to turn the pile each time you add new material.

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.

To learn more on the basics of composting, check out this article.

If you have a hot compost pile, add a small amount of ash along with other new materials every month or so while it is active.

If the pile is cold or rarely added to, only add ash in the fall or late summer, allowing time for everything to break down before being used in the garden during the growing season.

You can collect ashes and store them in a covered container through the winter.

Adding It Directly to the Garden

If you have determined via a test that your pH is low – below 6.5 – you can also choose to add ashes directly to the garden to reduce acidity.

Incorporating ashes can also increase the bioavailability of potassium, phosphorus, and various micronutrients, thereby increasing fertility.

A Note of Caution:

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.

Spread on calm days to prevent it from blowing around and scattering to unwanted areas – including all over your clothes.

Apply in moderation, lightly dusting a small amount on the garden surface and working it into the soil several inches deep with a fork.

According to Rosie Lerner, Horticulture Specialist at Purdue University, “Acidic soils (pH less than 5.5) will likely be improved by wood ash addition.

Soils that are slightly acidic (pH 6.0 to 6.5) should not be harmed by the application of 20 pounds per 100 square feet annually, if the ash is worked into the soil about six inches or so.”

Be sure to test the soil again the following year. You can reapply if the pH is still too low, but if it has reached 6.5, don’t add any more. If you raise the pH too much, this can deplete the bioavailability of essential nutrients.

Do not apply to acid-loving plants such as blueberries, rhododendrons, or azaleas.

Continue to test your soil every few years and amend as necessary.

Ashes to Dust

While it is never wise to dump a whole bucket on your compost or in the garden beds, used in moderation with careful planning and an understanding of your soil, wood ashes can be repurposed as a useful amendment.

Though my wood stove churns out far more than I can safely use each winter, I am still able to recycle much of it back into my compost.

Have you used wood ashes in your garden? Please share your experience in the comments below!

If you enjoyed this article, you can learn more composting tricks in these guides:

• Compost Tea: It Feeds and Protects Your Plants
• How to Use Eggshells in the Garden for Soil, Compost, and as Pest Control
• How to Start Worm Farming: Adventures in Composting and Vermiculture

© Ask the Experts, LLC. ALL RIGHTS RESERVED. See our TOS for more details. Uncredited photos: Shutterstock. With additional writing and editing by Clare Groom and Allison Sidhu.

Can I Compost Ashes (The Truth about Ashes in Compost)

Understanding if and how you should use ashes in compost can be confusing.

For example, you hear a lot of gardeners using ashes as fertilizer in the soil. So should you just throw it directly onto earth, or is it better to put it in compost?

And if you regularly use a fireplace or stove, you probably accumulate a lot of this waste material. 

So what’s the best way to deal with it?

In this article, I’ll explain the ideal way to include ashes in your home composting and how to avoid the possible side effects of using ash for the garden.

Ashes are an excellent addition to compost because they are high in potassium and other micronutrients. It helps make compost more versatile for soil amendment. Ashes are also very alkaline and help modify the pH values of compost. But not all types of ashes are ideal for composting.

Ashes are known to be a good source of potassium (they contain up to 10% potash). 

Potassium is needed by plants to create chlorophyll, the amazing substance that makes photosynthesis possible. It can also help make plants more disease-resistant. 

Ash is also high in calcium (up to 25%). Calcium carbonate is a well-known limining material. In other words, it increases alkalinity levels.

On top of that, ashes contain many other valuable micronutrients, such as magnesium, phosphorus, iron, boron, zinc, and manganese.

Compost made with ashes will have an increased spectrum of nutrients. The larger the variety of organic matter you put in your compost, the better it can replenish nutrients in the soil.

One of the beneficial side effects of using ash in compost is that it helps neutralize odors.

You should also know that ashes can strongly affect acidity levels. In addition, they contain soluble salts, which can be potentially harmful to plants. For these reasons, it can be more beneficial to put ashes into a compost bin rather than spreading them directly in the garden.

But a word of warning…

You need to consider the origin of your ashes to ensure they don’t harm your compost and gardening efforts. 

Are ashes bad for compost?

Ashes are generally considered good for composting. This is because not only are ashes high in potassium, but they also contain a good amount of calcium. This is a common liming material for correcting acidity. But it can be confusing to know the correct type of ashes to use and how to use them.

As a general rule, you might be better off composting ashes than adding them to the soil.

There are a couple of reasons for this.

The soluble salts contained in ashes are possibly harmful to some plants. When you put ashes into compost, these salts are slowly washed away. Heavy rainfall and watering encourage the salts to leach out.

Ashes are also very alkaline. So adding them to soil lowers acidity levels. This is good if you know your soil is overly acidic, but avoid overdoing things. However, compost is quite acidic, especially in the early stages of decomposition. So adding ashes can therefore help balance pH levels in your compost.

One crucial thing to keep in mind is where do your ashes come from?

There are a few situations where you don’t want to use ashes at all…

Can I compost charcoal ashes? 

The term “charcoal” refers to the manmade type of coal made from burning wood. Ash produced from charcoal results in the correct type of ashes for adding to compost.

It’s essential to understand the type of ashes you use for composting.

The powdery residue that remains after a wood fire in stoves and fireplaces is good to compost.  

Keep in mind that the type of wood you burn slightly impacts the level of beneficial potassium contained in the ashes. For example, young wood will result in higher potassium levels than old-aged wood.

You should also make sure the wood used in the fire is not treated wood. Chemically treated timber could leave trace residues which might be harmful if put in compost.

Can you put coal ashes in compost?

Natural coal is a mined mineral that includes heavy metals, chemicals, and sulfur traces. These substances are potentially toxic for plants. So ashes from mined raw coal should not be composted.

As you can see, it’s helpful to understand the source of your ashes if you want to avoid adverse effects on your compost biology and plant health.

Can I compost fireplace ashes? 

Fireplace ashes can be composted if the fuel used in the fire is wood. Do not use fireplace ashes if you use natural coal or artificial firelogs. Also, avoid ashes from burnt, treated timber.

Fireplace ashes generally refer to the powdery substance remaining after a wood fire. This is safe to use if you know the wood is from a natural, untreated source. If the wood was painted or stained, then avoid using the ashes.

Can I put wood ashes in compost? 

Wood ashes are safe to use in compost. This is the best type of ash to add to a compost bin. Wood from young trees will give you the best potassium content

Can I compost paper ashes? 

Paper is generally made from wood pulp and contains cellulose. Some paper uses cotton, but both these materials are organic and can be safely used after burning. 

Remember that the paper-making process reduces the amount of beneficial nutrients in the paper, adding less goodness to your compost heap.

Can you compost ash from BBQ?

Avoid using ashes leftover from a barbecue. It can be contaminated with fats from cooked meat. Also, if the barbecue was started with chemical firelighters, the ashes could be contaminated with harmful chemicals.

Even if you used natural wood charcoal as fuel for your barbecue, the resulting ashes could still end up with contaminants. If you add these to compost, they will harm composting microbes.

Ash is relatively high in carbon. This makes it a brown composting material. The calcium carbonate content of ashes also makes it strongly alkaline, so you need to be aware of its effect on your compost heap.

The C: N ratio of ashes is 25:1. In other words, it is 25% organic carbon. 

Thanks to the calcium carbonate content, it is more alkaline in nature. 

Wood ashes are alkaline in nature. Ashes have a liming effect which means they help neutralize acidity. When added to compost, they make it more alkaline.

Wood ash is very alkaline, with a pH level between 9 and 11. Adding them to compost helps neutralize acidity levels. Adding them to fresh composting materials makes sense because compost usually starts out on the acidic side. 

Remember that pH measures the acidity or alkalinity of a substance. A pH of around 7 is considered neutral.

The resulting ash compost can be good for very acidic soils. Use it as mulch around lime-loving plants. But avoid using it on acid-loving fruit bushes like blueberries or raspberries and flowering plants like rhododendrons.

The most important plant nutrients are most readily available in somewhat neutral soil (pH of 7). However, some micronutrients become more freely available when the soil is slightly acidic (pH between 5,5 and 6).

Adding ash compost to soil can be an excellent way to achieve an optimal pH range for plants between 6.2 and 7.3

It’s always a good idea to test your soil pH beforehand so you know the starting point of your soil.  

A soil test kit like this one (Amazon) gives quick results, but if you want a more lasting solution, you can get some excellent pH and moisture meters like this one.

Add small amounts of ash to your compost heap. As a general rule, sprinkle a thin layer of ash every 12 to 18 inches of organic matter. Avoid using too much ash at a time because of its high alkalinity. 

You should try to remove any large unconsumed pieces of wood using a garden sieve – here’s an example on Amazon. 

How much ash should I put in my compost?

You only need to add a thin layer of wood ash for every foot or so of organic materials. 

Some nutrients can get washed out if your compost isn’t covered and gets soaked by rainwater. This includes the unwanted salts, but also some of the beneficial potassium. To counteract this, it’s a good idea to add several layers of ash as you build up your compost heap.

Can you put too much ash in compost?

It is possible to use too much ash when composting, so avoid excessive ash doses. Considering the high alkalinity of ash, you should limit the amount of wood ash to thin layers. 

Too much potash can unbalance the pH levels of compost. Composting microbes and fungi work most efficiently at a neutral range of pH values. 

Avoid adding large amounts of ash, especially to more mature compost, which is already more alkaline than fresh compost.

Features and secrets of feeding plants with wood ash

Wood ash as waste in rural areas often accumulates in enormous quantities. At the same time, knowledgeable summer residents find it quite reasonable to use it as a natural fertilizer for feeding various plants. The high content of potassium, magnesium and calcium in the ash really motivate such use, however, this growth stimulation option may not always be appropriate. There are certain nuances that must be considered when using such a natural fertilizer. nine0004