Ash As Fertilizer: Useful Or Not?

If you want to use ash as fertilizer, you need to consider a few things. Ash from natural wood is suitable. However, if the ash comes from barbecue charcoal or treated wood, it will cause damage in the garden. Learn now how to properly use ash as fertilizer.

Ash as fertilizer: the most important facts at a glance

  • Wood ash contains up to 45 percent quicklime. Caution is therefore advised when handling it. Quicklime is alkaline and can severely damage foliage.
  • It is not possible to estimate the percentage of heavy metals in the ash. To be sure, you would have to hire an expensive test.
  • Ash for fertilizing the garden should come from untreated combustibles such as wood, straw or other plant matter.

Do not apply ash to permeable, sandy soils. You will damage soil life by doing so.
Ash fertilizer may be considered on heavy soils with high clay or loam content.
Certain plants, such as fruit trees, tomatoes or geraniums, benefit from ash, but others do not tolerate it at all. Find out in advance which crops you can use wood ash as a fertilizer for.
Is ash suitable for fertilizing the garden? After all, wood ash contains many nutrients that can benefit plants. Garden owners who recycle everything in their garden see ash as part of a natural cycle. This article clarifies if and how using ash as fertilizer works in the garden.

Can ash be used as fertilizer?

Not all ash is the same, so there is no clear answer to this question. It depends on the components, which can be determined by the origin of the fuel. The nutrients contained in ash are readily available to plants. This is due to the fact that carbon dioxide escapes during combustion and the organic matter remains in the ash. Lime is also contained in a more available form. Ash thus shows rapid effects, but overfertilization happens quickly.

If the ash comes from young and untreated wood, the quality of the ash is better than if you burn varnished wood or briquettes. If you fire your stove or fireplace with colorfully printed catalog pages, for example, residues of the inks will get into the ash. Fortunately, modern printing inks are generally not contaminated with heavy metals. Nevertheless, there are ingredients that are questionable from an environmental point of view.

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Ash as fertilizer

The critical thing about ash fertilization is that you don’t know exactly what pollutants and ingredients are in it. You are practically fertilizing blindly and hoping it will be fine. Each ash has a different composition and you don’t know what the percentage of minerals or heavy metals is. It is virtually impossible to make a controlled fertilization with it. Instead, you run the risk of introducing toxic substances into the soil.

Ash produced by burning barbecue charcoal or briquettes is particularly critical. You should always dispose of these in the household waste. In the case of barbecue coal, there is a risk that fat from the barbecue food will drip down and change in the embers into a questionable waste product such as acrylamide. This should not be added to their soil under any circumstances.

Alkaline ash as fertilizer has disadvantages

Wood ash has a high pH of between 11 and 13, depending on the quicklime and magnesium oxide content. The high calcium content in the ash is very aggressive. It is also called quicklime. Now, one might think that quicklime could be used to lime a garden soil or lawn after all, but the alkaline ash brings with it two decisive disadvantages:

  • If the ash gets on the foliage, it can cause severe leaf burns.
  • If you apply ash to light soils with a high sand content, you can severely damage soil life.
  • In any case, you should be prudent with ash as a fertilizer.

Good ash, bad ash: which is most suitable as a fertilizer?

When it comes to the question of ash as a fertilizer in the garden, opinions differ widely. This is due to the fact that each ash is different. Depending on the fuel used, it may contain substances that are harmful to humans, animals, plants and the soil. So you should pay attention to what you and burn and also how you light the combustible. If, for example, accelerants or barbecue lighters are used, the pollutant content in the ash increases.

Components of wood ash

Wood ash mainly contains calcium or calcium oxide, known as quicklime. This can account for up to 45 percent. Magnesium and potassium are also present, as well as phosphorus pentoxide. Iron, manganese, sodium and other mineral trace elements can also be found. If the wood ash originates from treated wood, heavy metals may also remain in it. These are, for example, lead and chromium as well as cadmium – as fertilizer a toxic cocktail for plants and animals.

  • Unsuitable fuel for fertilizer ash
  • Hard coal
  • Lignite
  • Pellets
  • Tobacco
  • briquettes
  • impregnated garden wood such as fence posts, poles or old terrace wood
  • treated wooden furniture
  • chipboard
  • panelling
  • treated recycled wood
  • varnished, glued, stained wood
  • color printed paper, catalogs
  • cardboard
  • glossy paper
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Suitable fuel for manure ash

Primarily, untreated wood, straw, or plant material that comes from trees, shrubs, and other plants that have been allowed to grow in a clean location is suitable. It is best to light the fuel with paper that does not contain any substances of concern. You can consider the resulting ash for use in the garden as fertilizer.

Ash As Fertilizer: Useful Or Not?

If you have purchased a large quantity of firewood from one batch and would like to use the ash in the garden, you should have it tested for heavy metal content. Find out exactly how to do this on the testing laboratory’s site. The cost of the chemical testing laboratory is 100 to 150 euros. After that, you will have certainty as to which components are contained and can use the ash later in a targeted and, above all, controlled manner. With such a high investment, however, one wonders whether it is better to simply use classic fertilizer for your plants.

Since ash usually accumulates more in winter, you can store it in an ash bucket until the next gardening season. Containers made of alkali-resistant plastic are also suitable. Make sure that the ashes remain dry.

Here’s how you can use ash as fertilizer in the garden

You can use ash in the garden in a variety of ways. The following four application options are available to you.

  1. scattering
    And to target large areas with the fertilizer ash, you can spread it directly into the bed. Rake the ash in superficially afterwards. In this way, you will avoid the ash being carried away by the wind. How many grams of ash to apply per square meter depends on the pH of the soil on the one hand and the pH of the wood ash on the other.

Example: If the soil is in the pH range of 4, 200 to 400 grams of ash per square meter is suitable. Less acidic soils will do with 20 to 100 grams per square meter.

  1. mix with soil
    Mixing ash with soil, you can use the mixture for planters. To avoid over-fertilization, it has proven effective to mix the ash with sand or stone dust beforehand and then add it to the soil.
  2. watering
    Mix ashes into watering water and apply the mixture with a can when watering your plants. This procedure is especially recommended on windy days.
  3. compost
    Another way to use ash for fertilization is to mix it with compost. If the ash is highly alkaline, add a small amount to the compost in layers. A thin layer of ash is followed by an alternating layer of organic waste. In this way, you can enrich the compost pile with wood ash step by step.
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What plants are suitable for fertilizing with ash?

Wood ash can be used in the lawn and beds. Mosses and algae are killed by it. Also, many root weedsyou destroy with ash, because they do not tolerate it and die. But there are also crops that you must not fertilize with ash under any circumstances. And on the other hand, certain plants benefit from wood ash.

You may fertilize these plants with wood ash

As a general rule, you should refrain from using ash from fuel of unknown origin as fertilizer. If there are pollutants in it and you fertilize your vegetables with it, you will absorb the toxins yourself via this detour. In general, ash benefits plants that require alkaline or neutral soils as their location. First and foremost, these are fruit trees and vegetable plants. However, some ornamental plants also tolerate ash:

  • Cherry, apple, pear, plum and other fruit trees.
  • Raspberries
  • Gooseberries
  • carrots
  • Celery
  • Tomatoes
  • Onions
  • Leeks
  • Fuchsias
  • Geraniums
  • Lavender
  • Carnations
  • Chrysanthemums
Ash As Fertilizer: Useful Or Not?

These plants do not tolerate ash fertilization.

If plants prefer acidic soil, ash is unsuitable as a fertilizer. Plants that have their natural habitat in bogs should also not be treated with ash:

  • Azaleas
  • Rhododendrons
  • Blueberries
  • Cranberries
  • Camellias
  • Peonies


  • James Jones

    Meet James Jones, a passionate gardening writer whose words bloom with the wisdom of an experienced horticulturist. With a deep-rooted love for all things green, James has dedicated his life to sharing the art and science of gardening with the world. James's words have found their way into countless publications, and his gardening insights have inspired a new generation of green thumbs. His commitment to sustainability and environmental stewardship shines through in every article he crafts.

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