Last updated on October 23rd, 2023 at 09:00 pm

Be it through the barbecue, a nice campfire in the summer or through the tile or Swedish stove in the winter. If you take a closer look, you produce quite a lot of ash.

If you ask yourself whether you can use ash as fertilizer, then you are exactly right.

Because I explain to you, with which ash you can fertilize which plants.

Ash from natural wood, straw or plant waste can be used for fertilizing. Pellet ash, paper ash or barbecue ash often contains chemical additives, such as binders, colors or oils, which is why it is not suitable for fertilizing.

Use Ash As Fertilizer: What Ash Is Good For?

Ash is suitable for use as a natural, 100% organic fertilizer especially for clayey and loamy soils, i.e. very heavy soils overall. These tolerate the strongly alkaline fertilizer better than light, sandy soils for which, for example, eggshells or lime are more suitable as fertilizers.

Although ash, unlike other fertilizers does not contain nitrogen, it consists of four other very valuable nutrients: Calcium oxide (so-called quicklime), potassium oxide, magnesium oxide and phosphorus oxide.

All these substances are also present in this or a modified form in classic NPK fertilizers, among others.

Since ash is very easily soluble, it develops the fertilizing effect in the soil very quickly. Due to the quicklime, of which ash mainly consists, ash also has a much stronger effect than, for example, conventional lime.

Therefore, ash should be used as fertilizer with caution, especially for heavy soils and initially in small quantities so as not to harm the soil.

Which ash to use as fertilizer

Ash from 100% natural, young wood is best for fertilizing.

This is because natural wood, i.e. wood that has not been chemically or industrially treated, does not have any residues of industrial substances. In addition, young wood has a lower pollutant load and therefore does not pollute the garden when fertilizing.

When choosing the wood from which you will extract ash for fertilizing, you should therefore pay attention to the following points:

Always use ash from 100% natural wood for fertilizing.

It is best if you know where the tree – whose ash you use for fertilizing – has stood before. Then you can be completely sure about the origin and location.

When you burn wood, it should always be natural. That is, without residues of paint, varnish or other industrial substances. If you burn these, toxic gases are produced on the one hand, and on the other hand, residues remain in the ash.

If you would then use this ash for fertilizing, the unnatural or maybe even toxic residues would also get into your garden and e.g. the vegetables.

The ashes of young wood for fertilizing are better than those of older wood.
In principle, the ash from younger wood is better for fertilizing than that from older wood.

This is because the trunk or wood of a tree has absorbed all external influences over the life of the tree and now bears the marks of them.

A tree can live for several decades or sometimes centuries without any problems. The tree is completely exposed to all environmental influences and to a certain degree also absorbs substances from its environment into the trunk, the leaves or the bark.

If you now burn the wood of a tree, you also burn the substances absorbed in the wood over the years, such as heavy metals or other particles that come from the air.

A young tree that is not yet so old could of course not yet absorb so many negative substances in bark and wood, which is why its ash is better, more compatible and less polluted for your garden.

Tip.

If possible, do not use ash from trees that were located on busy roads. The fine dust pollution can be very high there, which is reflected in the ash.

Overview: what ash can be used as fertilizer

Is wood ash a good fertilizer?

Wood ash, which is produced by burning wood, is a very good fertilizer, especially when young, natural wood is used.

Since wood ash contains many different oxides, such as calcium, magnesium, potassium or phosphorus oxide, it is suitable as a fertilizer to provide plants with valuable nutrients.

Wood ash is a good fertilizer insofar as it acts very quickly and also intensively, i.e. it develops its effect in the soil directly after fertilizing.

Especially in heavy, poorly permeable soils (e.g. clay or loam), wood ash can be beneficial as a fertilizer.

Pellet ash as fertilizer

If no additional substances are used in the production of pellets, such as binders made of kerosene or molasses, pellet ash can be used as fertilizer

Pellets are made from dried wood waste or wood chips. To make the pellets more durable and stable, binders such as kerosene (oily or waxy substance), starch or molasses (sugar syrup) are sometimes used in the production process.

So if you use ash from pellets with binders as fertilizer, these binders will also get into your garden which is not ideal especially with kerosene.

Therefore, it is best to buy pellets without binders, so that you can also use the ash afterwards for fertilizing.

Barbecue ash as fertilizer

Theoretically, barbecue ash can be used as fertilizer for the garden, as it is usually made from barbecue briquettes or charcoal and thus has its origin in wood. However, due to the unsustainable or regional origin of the wood used for barbecue charcoal and briquettes and the barbecue residue in the ash, the use of barbecue ash as fertilizer is not recommended.

More specifically, the wood from which barbecue briquettes and charcoal are made often comes from rainforests and is therefore not regionally or sustainably grown.

In addition, oil or grease can drip onto the charcoal during grilling, which ends up as greasy residue in the ash and is not ideal. Thus, I would advise against fertilizing your garden with the ashes from barbecue briquettes or barbecue or charcoal.

Ash from the fireplace as fertilizer

Ashes from the fireplace can also be used as fertilizer because usually only natural, untreated wood may be burned in the fireplace or stove.

If there are no chemical or other harmful or industrial substances, such as paints or varnishes, in the burned wood, ash from the fireplace can also be used as fertilizer.

Paper ash as fertilizer

Paper ash can be used as fertilizer, as long as pure white and no colored, painted or glued together paper was used.

Paper or cardboard is made in various steps from pulp, which in turn is made from wood. Thus, the origins of paper or cardboard lie in wood or trees, whose ashes are suitable as fertilizer.

However, the ash from paper that has been further processed or treated should not be used for fertilizer. This is because paints or adhesives that may adhere to the paper can produce toxic fumes when burned, and residues of these can also be found in the ash.

Cigarette ash as fertilizer

Cigarette ash should in no case be used as fertilizer, because a possible pollution can be much higher than a possible, if at all very small fertilizing effect.

More precisely, cigarette ash contains only about 1% potassium which has a positive fertilizing effect. At the same time, however, cigarette ash contains toxic soot and heavy metals, which would have a negative impact on the soil.

Therefore, cigarette ash should be disposed of in the residual waste and not used as fertilizer in the garden.

What plants can be fertilized with wood ash?

Ash has a very high pH of about 11-13 which is why ash as a fertilizer is ideal for plants that like an alkaline or alkaline soil.

In the following table I have summarized all the flowers, ornamental shrubs, fruits, vegetables and herbs for which you can use ash as fertilizer.

Was a plant you were looking for not included in the list? Then it may be a more acid-loving plant that you can fertilize very well with coffee grounds.

Ash as a fertilizer for roses

Since roses need a neutral to slightly acidic soil (pH of 5.5-7.0), roses should not be fertilized with ash.

Although soils in Europe are slowly acidifying and thus should be limed from time to time, ash is too aggressive a fertilizer for roses.

If the soil pH of your roses is too acidic (below 5.5) then at most you should fertilize lightly with lime, which has a less powerful effect than ash.

Ash as fertilizer for hydrangeas

Ash is not suitable as a fertilizer for hydrangeas because hydrangeas prefer an acidic soil (pH between 4.0-6.0) while ash increases the pH of the soil.

In the worst case, if you fertilize hydrangeas with ash, they will die because they cannot cope with alkaline soil.

If you’re looking for a natural fertilizer for hydrangeas, just use coffee grounds, which are acidic. You can read about how to use coffee grounds as a fertilizer here.

Ash as fertilizer for fruit trees

Ash can be used as a fertilizer for fruit trees without a problem, as they do very well with an alkaline soil and also make good use of the extra nutrients, such as potassium, from the ash.

Although ash has a strong alkaline effect, fruit trees do very well with ash due to their size and can be fertilized with it.

Ash as fertilizer for strawberries

Since strawberries have a neutral to slightly acidic soil (pH 5.5-7.0) which is why ash should not be used as a fertilizer for strawberries.

If the pH of strawberries should fall into the strongly acidic range, it should first be fertilized with normal, carbonic acid lime (such as algal lime). This is because the effect of lime is much weaker than that of ash.

If you still want to use ash to fertilize strawberries you should use very little and carefully monitor the evolution of pH.

Ash as fertilizer for vegetables

Ash can be used to fertilize vegetables with high nutrient requirements, so-called heavy feeders, which prefer a neutral to alkaline soil pH.

These include potatoes, cabbage, onion or leek.

Nevertheless, you should be careful when fertilizing vegetables with ash, so that the soil is not overfertilized.

So rather use less ash and check the pH value after fertilizing.

Ash as fertilizer for tomatoes

Ash can also be used as a fertilizer for tomatoes, since tomatoes are heavy feeders, so they can use the extra nutrients well and they prefer a neutral to slightly alkaline soil.

Nevertheless, tomatoes should be fertilized carefully with ash. This means using little ash at first and checking the pH after fertilizing so that a sense of the strength of the effect can be found.

Ash as fertilizer for the garden

In general, ash is very suitable as a fertilizer for the garden, because it contains many nutrients and can neutralize or raise the pH of the soil.

Nevertheless, care must be taken that only plants that also need a neutral or alkaline soil are fertilized with ash. These are, for example, fruit trees, potatoes or tomatoes.

On the other hand, plants that need an acidic soil, such as hydrangeas or rhododendrons, must not be fertilized with ash.

How to fertilize with ash?

Ash can be used to fertilize in two different ways: on the one hand, directly, by spreading ash on the soil. On the other hand, you can also fertilize indirectly with ash by spreading it on the compost or adding it to the irrigation water.

When fertilizing with ash, you should always follow these two rules:

• Never apply ash in conjunction with ammonium-containing fertilizers, such as slurry or manure or mineral nitrogen fertilizers. This would produce toxic, gaseous ammonia.
• Never apply ash in conjunction with mineral phosphates or phosphate-containing fertilizers. This would produce calcium phosphate, which is very difficult to dissolve and cannot be absorbed by plants.

Direct fertilization with ash

The easiest way to fertilize your garden with ash is to apply it directly to the soil or to work it in lightly.

For this purpose, it is best to use a small shovel with which you can spread the ash from the ash bucket onto the soil.

The direct fertilizing with ash is best done when there is no wind, otherwise the ash will blow away and can reach places in the garden where you did not want to spread it.

Alternatively, you can moisten the ash in the bucket very slightly so that it becomes heavier and easier to spread.

So after you spread the ashes on the ground, it’s best to water the garden a little afterwards. This way, the ash will get directly under the soil or combine with it.

It is even better if you lightly work the scattered ash directly into the soil. This way, the nutrients get into the soil even better.

Just make sure that you do not scatter the ash directly over leaves or vegetables, for example, as the plants ultimately absorb the main part of the nutrients through the roots.

Indirect fertilization with ash

If you don’t want to scatter the ash directly on the soil there are two alternatives to indirect fertilizing with ash:

Dissolve the ash in the irrigation water and then water your flowers or garden with it.
Add a thin layer of ash to the compost from time to time, so that the humus is directly enriched with the appropriate nutrients. Ash on the compost is a great alternative to traditional lime fertilizer.

How often to fertilize with ash?

How often you should fertilize with ash depends entirely on what kind of soil you have in your garden. Here we distinguish between two types of soils:

How often to fertilize acidic soils with ash.

Acidic soils, such as bog soil, sandy soil or loamy sand, can be fertilized without problems every 3-4 years with about 200-400 grams of ash per square meter. Converted, you can thus apply about 70-100 grams of ash per year per square meter.

How often to fertilize less acidic soils with ash

Less acidic soils, such as clayey soil or loess soil, you can fertilize every 3-4 years with about 100-200 grams of ash per square meter. On a yearly basis, you can fertilize with about 30-60 grams of ash per square meter.