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Is Ash Good for Compost? What You Need To Know!

ashes residue

Using wood ash in compost can be a huge benefit for your garden. When your summertime backyard fires die down or you dampen the roaring fireplace that keeps you warm in the winter, you’ll have tons of quality wood ash remaining. Rather than deal with disposing of it, learn how you can add this alkaline and nutrient-rich resource to your compost for an extra-abundant garden.

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Is Ash Good for Compost?

Wood ash from a fireplace can be a positive addition to compost, as its alkalinity can help neutralize overly acidic soil. It also introduces beneficial nutrients like calcium and potassium as well as trace amounts of other minerals including zinc, magnesium, and phosphorus. The lack of nitrogen in wood ash allows for its use alongside fertilizing components of compost without the added risk of burning your plants.

ashes from burnt wood
Image Credit: Alexas_Fotos, Pixabay

How to Use Ash Directly

Before adding wood ash to your compost, you must ensure your soil will benefit from it. Use a home testing kit to check the pH levels of your soil and obtain other nutrient information. If your soil is too acidic or deficient in the nutrients needed to grow your plants, wood ash could be a viable supplement.

If your soil has low pH or potassium levels, you can apply wood ash directly to the soil around your plants. Sprinkle a light dusting on the soil’s surface and work it a few inches into the ground with a rake. The best time to apply it is on a calm winter day when the wind won’t displace the loose ash. You can also mix it into the soil around growing plants—particularly fruiting vegetables.

Keep the application relatively light, as adding too much ash can limit vital nutrients such as iron. If the pH is around 6.0, you can safely use about 1 pound per 5 square feet of earth. Make sure to test the soil every year and add more if needed.

How to Use Ash in Compost

Adding ash to compost is an excellent method for managing its natural tendency to become acidic over time. It also helps to expedite the decomposition of worms, and it can repel garden nuisances like slugs. By adding your ash to compost rather than directly into the ground, you reduce the potential for any damage to the soil’s health.

Incorporate ash into your compost heap as you build it. If you add ash later, it can cause the pH to spike and create toxic soil characteristics.

Wood ash should take up no more than 5% of your compost heap’s constitution. When building it, make sure it consists of roughly 75% carbon-rich brown material, like leaves, dried grass, and hay, and about 25% nitrogen-rich green material, such as food scraps and tea bags. If you layer 3” of green material to start, add 9” of brown material and then about ⅛” of ash on top.

You can adjust the thickness of the three layers, but make sure you keep the ratio intact. Keep alternating these layers as you build the heap. Use a pitchfork to turn the layers each time you add a new one.

As you use the compost heap throughout the growing season, you’ll likely need to add more ash layers in similar proportions to additional brown and green materials. At the end of the season, if you have a leftover pile you want to save for next year, you can add ash to it if you haven’t done so already. The winter months will give it time to break down and incorporate so that it doesn’t overbalance your soil in the spring.

Garden shovel in a container filled with ash
Image Credit: NordHelena, Shutterstock

When You Shouldn’t Use Wood Ash

While wood ash can help plants that need neutral soil pH, it isn’t ideal for plants that enjoy acidic soil. Many evergreen trees prefer lower soil pH, and popular flowers like rhododendrons, daffodils, azaleas, and hydrangeas also enjoy a more acidic environment. Before using wood ash, be safe by researching the soil needs of your garden plants.

What Types of Ash Can You Use in Fertilizer?

Fireplace ash is safe to use in an organic garden because it’s free of chemicals and soil-harming substances. Ash from treated lumber, charcoal used in grills, or burned trash can introduce harmful residues, so you must be careful to keep it away from the compost.

Many people may also be interested in incorporating human ashes into the soil in tribute to a deceased loved one. While a small amount will generally be harmless, cremated remains contain a high level of salt, which can prevent any vegetation from growing. Instead of using ashes directly in the soil, you can look into special containers that some companies sell for growing plants with human remains.

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Final Thoughts

Incorporating wood ash into your compost heap is a clever way to recycle leftovers from a summer bonfire or an indoor fireplace. Store it on hand in airtight containers, ready for use when you need to amend your soil’s acidity. By following these tips on adding ash to compost, you’ll love how convenient it can be to keep your garden thriving.


Featured Image Credit: ivabalk, Pixabay

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