Wood ashes in compost

Learn More About Using Ashes In Compost

Is ash good for compost? Yes. Since ashes do not contain nitrogen and will not burn plants, they can be useful in the garden, especially in the compost pile. Wood ash compost can be a valuable source of lime, potassium, and other trace elements.

Fireplace Ashes for Compost

Composting ashes is an ideal way to put them to use in the garden. Fireplace ashes for compost can be used to help maintain the neutral condition of the compost. It can also add nutrients to the soil. Decomposing materials in the compost pile can become somewhat acidic and wood ash can help offset this, as it’s more alkaline in nature.

However, it may not be a good idea to use charcoal ashes, such as those from grills. Compost with charcoal can have chemical residue from the additives in the charcoal. These chemicals can be harmful to plants, especially when used in large amounts. Therefore, it is better to stick with wood ash—provided that the wood used has not been treated or painted.

Using Wood Ash Compost Instead of Direct Ash Applications

Ashes tend to raise the soil pH, so you shouldn’t use it directly on plants, especially acid-loving ones like rhododendrons, azaleas, and blueberries. Also, in high amounts, wood ash can inhibit plant growth by restricting nutrients, like iron. Don’t apply it directly unless a soil test indicates a low pH level or low potassium. Adding wood ash within the compost pile, however, will lessen any chance of future issues and can be safely added to the soil as a balanced fertilizer.

In addition to improving the 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.

A question that often comes up when talking about different composting techniques is weather or not ash can be used in compost or the garden.

The answer is yes, you can compost wood ash from your fire pit or fireplace. There are a few caveats to this however and even depending on where you live can have great impacts on how much wood ash you should be adding to your compost or garden on its own.

If you’re like me, you love having the occasional bon-fire in the backyard with friends or family. Maybe, you like to enjoy the fireplace on a cold winter’s night. Or, maybe you even heat your home with wood. No matter what the reason, you have ended up with enough wood ashes to consider how to treat them so that they would benefit the garden best.

One of the biggest warnings you will ever hear about using wood ash in and around your lawn and garden, including in your compost pile, is that ash is very alkaline compared to most items you normally would add.

Soil is different around the world when it comes to its acidity. Depending on where you live, a soils “pH” will differ drastically. The pH scale will measure a soil’s acidity or it’s alkalinity. The scale ranges from 0 or extremely acid to 14, extremely alkaline. 7 is neutral. There is a great page explaining Soil pH at the ESF SUNY College of Environmental Science and Forestry’s website but for the sake of our conversation here, just know that most plants like a slightly acidic soil of 6.5.

Before we get into using wood ash in the compost or on its own in the garden, it is pretty important that you have an understanding of your garden’s pH. This really will only pertain if you are planning to use a large amount of wood ash or on a regular basis in the garden and pile.

The reason for this is that wood ash, from the most common hard-woods and some soft-woods is naturally very alkaline. Like somewhere in the 9 or higher range of pH. When adding a substance of this alkalinity to your compost pile, let alone your garden itself, it can drastically change the soil’s pH without question.

Like I mentioned earlier though, if you’re only using a small amount, like under a pound or two in an entire season’s worth of composting, you will most likely be fine as the volume of other materials in the pile over that time will dilute the alkalinity down to normal 6.5 to 7.

If you plan on testing your soil, which I recommend if you are going to be adding ash regularly to your composting regimen, I suggest getting a simple soil pH testing kit. These kits are affordable and usually can be used several times if not indefinitely. For a list of the ones that I have used in the past or that I recommend, check out the soil test kits at our Tools For Composting page.

Now don’t let me scare you here about adding wood ash to your compost pile. In most cases, the addition of some ash every now and then will usually help and depending on what your soil’s pH ends up being, the benefits of it will far outweigh the risks.

Some cautionary advise. I never have had any reason to add wood ask directly to the garden or lawn directly. I have always added it to my compost and let it break down there. The reason is that I’d prefer that it break down in the compost pile and let the minerals dilute there and then add that to the garden later. This reduces the risk of drastically increasing your soil’s pH in any one area in the garden.

Plants That Do Not Like Highly Alkaline Soil
With all that said, some plants that probably really won’t need any addition of wood ash or highly alkaline compost will include…

  • Azaleas
  • Rhododendrons
  • Chrysanthemums (mums)
  • Marigolds
  • Daffodils
  • Hydrangeas
  • Blueberries
  • Magnolia Trees
  • Holly Shrubs

If your yard contains a large amount of these plants, and they seem to be doing very well, you may want to hold back on adding any wood ash to the compost.

What Makes Up Good Wood Ash To Add To The Compost Heap?
The best kind of wood ash to use is from any of the good hard woods such as Oak, Maple, and Birch. Sometimes you might get your hands on some Cherry or Walnut to add to the fire as well.

Second best to the pit would be your softwoods like pine and fir. Most people avoid burning these because they burn quickly and are very sappy, which tends to cause more sparks than normal. Sometimes not a good thing.

Woods to avoid using for adding to your compost would include anything that has been treated or painted. These have chemicals that leave a chemical residue after burning that can get transferred to the garden and eventually affect your plants. Besides, burning these things aren’t good for your health either.

What Makes Wood Ashes So Good?
Wood ash is very vital to the garden when used properly, that before the times of fertilizers, it may have made the difference between an o.k harvest versus a great bounty on the homestead.

Wood ashes contain many micronutrients and minerals that greatly benefit your vegetables and plants at home. Some of these elements include…

  • Calcium
  • Potassium
  • Magnesium
  • Phosphorus
  • Manganese
  • Chromium
  • Copper
  • Nickel
  • Zinc

The above list is in order of highest to lowest of its concentration within the wood ash.

Calcium, for example, makes up about 15% of the total mass within the ash which is by far the most prevalent mineral within.

However, if you were to use ground limestone, which is commonly used to raise a soils alkalinity in the garden, as a comparison. The limestone has about a 31% concentration of Calcium.

A good resource on this matter is a University of Georgia page on using wood ash for as a soil amendment.

Using Your Wood Ash
When it comes to composting on a regular basis, many people have a “multi-stage” composting system in place where they have several bins or piles of compost at different stages of completeness. In these situations, you can add small amounts of ash to the first stage of the pile every month or so during the active season Spring to late Summer). This can be mixed in with all your vegetable scraps, grass clippings and carbon materials.

As your pile progress through to the next stage or two, the wood ash will gradually break down with everything else and be thoroughly mixed in by the time the compost is complete.

If you are just running a single compost pile or bin you may want to spread the amount of time you add ashes to the pile or just reduce the volume you throw in. If you actively attend the compost pile, adding and mixing up the materials on a regular basis, considered a “hot” compost pile, you should also be ok with once a month or so.

If the compost you are working on is rarely used, and is considered to be a “cold” compost pile, you should really only add the wood ashes in the fall or late summer. Or, after you have used any compost from the pile for the last time that year.

This way, the ash will have a chance to break down slowly in the pile over time.

Using Wood Ash on its Own In the Garden
If you plan on using the wood ash on its own, without composting, which I don’t recommend in most cases. I would suggest that you use a soil pH kit for sure in this case.

Once you know exactly where in the yard or garden that the soil levels are much too acidic for the plants in that area to thrive, you can add a small amount around plants or on the soil.

Generally, you don’t want to have the wood ash in direct contact with the roots of plants so don’t mix it directly in against the plants. Instead, leave it on the top of the soil and let nature gently bring the minerals down to the plant with regular watering and natural absoption.

If the soil in your garden is in drastic need for amendment, either more alkaline or more acidic, you can find some suggested products at the Tools For Composting page.

Whether you decide to use wood ash in your garden or in your compost pile, if done correctly, you will find that it is a fantastic way to help your plants thrive and in the case of vegetables, you could get some great tasting and large ones for years to come.

Can I Compost Ash?

(From the Household waste category | )

You can compost some types of ash – but it’s best to avoid composting others.

You can compost:

  • Ashes from untreated and unpainted wood fires
  • Ashes from burning paper or cardboard
  • Ashes from burning grasses (such as straw)

These ashes are fine in small amounts – but be careful as it can very quickly made the heap to alkaline. (This might be desirable for balancing out acidic compost heaps or acid soils but in most circumstances, it’s better to keep it neutral overall.) Mix it into the contents of the heap to avoid the small particles being blown around on the wind.

Make sure ashes are thoroughly cooled before adding them to your compost heap, otherwise dry materials in the compost may fire risk.

These ashes can also be used “neat” on the garden as a slug deterrent and soil fertiliser, or reused in other ways too.

But don’t compost:

  • Ash from fires that have included treated/painted wood
  • Ash from fires that have included plastic or other synthetic materials
  • Ashes from fires included upholstered furniture (such as sofas) or mixed household waste
  • Ash from coal fires or peat fires
  • Ashes leftover in a charcoal barbecue
  • Ashes from fires that have been fuelled by commercials firelighters, lighter fluid or any type of petrol
  • Ash from cigarettes or cigars

All these types of ash contain materials that are harmful to plants or animals, or in some cases, the wider ecosystem.

If in doubt and especially if you’re using your compost for growing edibles, leave it out.

Wood ashes can benefit gardens and lawns

CORVALLIS, Ore. – As we move into the season of burning wood, consider saving the ashes for the lawn and garden, while remembering a few precautions.

Because wood ash is derived from plant material, it contains most of the 13 essential nutrients the soil supplies for plant growth, according to Dan Sullivan, OSU Extension soil scientist.

“When wood burns, nitrogen and sulfur are lost as gas,” Sullivan said, “but calcium, potassium, magnesium and other trace elements remain. The carbonates and oxides in the ash are valuable liming agents that can raise pH and help neutralize acid soils.”

The fertilizer value of wood ash depends on the type of wood. According to Sullivan, hardwoods produce about three times the ash and five times the nutrients per cord as softwoods. A cord of oak provides enough potassium for a garden 60 by 70 feet. A cord of Douglas fir ash supplies enough potassium for a garden 30 by 30 feet.

Both types of wood ash will reduce soil acidity slightly. Where soils are acid and low in potassium, wood ash is beneficial to most garden plants. Do not use ash if your soil pH is alkaline (more than 7.0).

Do not apply wood ash to acid-loving plants such as blueberries, rhododendrons and azaleas; nor to areas where potatoes will be planted; wood ash can promote potato scab.

Lawns that need lime and potassium also can benefit from wood ash. Apply no more than 10 to 15 pounds of ash per 1,000 square feet of lawn.

Wood ash also will add nutrients to compost. Mix it into your compost pile as you build the pile.

“Remember that wood ash is alkaline, which means it has a high pH level,” Sullivan said. “You should use the same precautions with it as when handling other strongly alkaline materials, such as household bleach.”

Among Sullivan’s suggestions:

  • Wear eye protection, gloves and a dust mask.
  • Do not scatter ashes in the wind. Apply recommended amounts to moist soil and rake lightly to mix.
  • Do not use ash from burning trash, cardboard, coal or pressure-treated, painted or stained wood. These materials can contain potentially harmful substances. For example, the glue in cardboard boxes and paper bags contains boron, an element that can inhibit plant growth at excessive levels.
  • Never leave wood ash in lumps or piles. If it is concentrated in one place, excessive salt from the ash can leach into the soil and create a harmful environment for plants.
  • Do not apply ash at time of seeding. Ash contains too many salts for seedlings.

17 Jan Using Wood Ash to Add Calcium to Your Organic Garden

Can I use all ash? No. Only wood ash will do. Ashes from coal, charcoal briquettes, or those faux logs will not cut it. These ashes can be thrown away, as they are of no use in the garden.

So how can I use wood ash in my garden?

Make a wood ash tea. Combine ashes with water, let the tea “steep” for a few days, and strain. The result, after brewing for a few days, is a potassium boost for plants that crave that extra potassium, like asparagus.

Sprinkle some on the lawn. Just a light layer will do, then thoroughly water in. If your lawn is needing lime and potassium, sprinkling wood ash is a great way to give your lawn the alkaline nutrients that it craves. Potassium helps your grass build thicker cell walls, which helps strengthen it. This strength comes in handy during times of stress, such as drought.

Feed your trees. The hardwood trees on your property will thank you forever if you spread a bit of wood ash cheer around their bases in late winter. Steer clear of using wood ash on trees like evergreen and juniper, however, as they require more acidic soil.

Compost. Adding some wood ash into your compost can increase the potassium and lime levels present. Decomposing materials within your compost can cause the compost to become acidic, which some plants may love. However, if you are looking to neutralize your compost for neutral or alkaline loving plants, adding wood ash is a great, easy, and organic way to achieve this. Make sure the wood is never treated with any sort of chemicals, as we only want to use organic in the garden. Adding wood ash to your compost comes with a caveat — a little wood ash in your compost pile is fine, but too much will over-alkalize your compost.

Use Wood Ashes in the Garden Wisely

You may have heard that wood ashes can be used in the garden as a source of potassium for plants. But since wood ashes also increase the soil pH and require other precautions, they should be used in the garden wisely.

Hardwoods vs. Softwoods

The fertilizer value and liming effect of wood ash depends on whether you burn hardwoods (e.g. oak) or softwoods (e.g. pine). Wood ash analyses generally run from 4-10% potassium and from 1-2% phosphorus. Compared to softwood ashes, hardwood ashes contain higher percentages of nutrients and have more of a liming effect on soil.

Avoiding Toxic Levels of Ash

Although hardwood ash is only about half as effective as lime for raising soil pH, it should still be used with caution. While some sources recommend a yearly application rate of 25-50 lbs. of ash per 1,000 square feet, other sources say apply no more than 10-15 lbs. of ash per 1,000 square feet per year.

Regular soil testing is suggested to monitor changes in soil pH and avoid toxic levels of ash. Some gardeners add small amounts to the compost pile, and then add the composted soil to the garden with good results.

Tips for Using Wood Ashes as a Soil or Compost Amendment

The following advice is offered from Dan Sullivan, soil scientist with the OSU Extension Service:

• Protect yourself when applying wood ash. Use the same precautions you would use when handling household bleach, another strongly alkaline material. Wear eye protection and gloves. Depending on the fineness of the ash, you may want to wear a dust mask.

• Do not use ash from burning trash, cardboard, coal or pressure-treated, painted or stained wood. These substances contain trace elements, harmful to many plants when applied in excessive amounts. For example, the glue in cardboard boxes and paper bags contains boron, an element toxic to many plant species at levels slightly higher than that required for normal growth.

• Do not use ash on alkaline soils or on acid-loving plants such as blueberries and azaleas.

• Do not apply wood ash to a potato patch as wood ashes may favor the development of potato scab.

• Do not apply ash to newly germinated seeds, as ash contains too many salts for seedlings.

• Do not add ash with nitrogen fertilizers such as ammonium sulfate (21-0-0-24S), urea (46-0-0) or ammonium nitrate (34-0-0). These fertilizers produce ammonia gas when placed in contact with high pH materials such as wood ash.

Traunfeld, J. and Nibali, E. (2013). Soil Amendments and Fertilizers. University of Maryland, HG42.

by Alicia Lamborn

Posted: October 4, 2017

Category: Florida-Friendly Landscaping, Fruits & Vegetables, Home Landscapes

Tags: pH, soil amendment, wood ashes

A reader writes in with a question about whether it is safe to compost ashes.

Can ashes from a fireplace be used in a compost pile? Would it be considered “brown” stuff rather than “green” stuff, The only things in the ashes would be newspaper, pine and other dried natural wood; nothing chemically treated.

The sort answer is yes, you can compost wood ashes, in limited quantities.

You don’t want to overwhelm your compost pile with too much of any single ingredient, whether it is ashes or anything else.

Ashes from coal or barbecue briquettes should NOT be composted, because they can contain chemicals that might harm your soil. (Although I must point out that there was a study by Washington State University that determined coal ash up to a certain percentage in compost didn’t harm anything. So maybe I’m just being overly cautious.)

I personally do not like composting wood ashes though, because ashes change the pH of the soil. Ashes are very alkaline.

In fact, if you live in a dry, desert area that already has poor, alkaline soil, you should avoid even wood ash.

Oregon State University Extension Agency has a very thorough article about wood ash and gardening and composting, that is mostly positive about using wood ash with gardening and with composting.

They also mention the pH issue.

For the home gardener, however, wood ash can be a valuable source of lime, potassium and trace elements.

“Since wood ash is derived from plant material, it contains most of the 13 essential nutrients the soil must supply for plant growth,” said Sullivan. “When wood burns, nitrogen and sulfur are lost as gases, and calcium, potassium, magnesium and trace element compounds remain. The carbonates and oxides remaining after wood burning are valuable liming agents, raising pH, thereby helping to neutralize acid soils.”

Where soils are acid and low in potassium, wood ash is beneficial to most garden plants except acid-loving plants such as blueberries, rhododendrons and azaleas. Use wood ash on flower beds, lawns and shrubs.

Hope this is helpful!

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