Especially in times of rising energy costs, a wood-burning stove in more and more households provides inexpensive heat. What appears to be a gray, dusty residue and is mostly disposed of in the garbage can is actually still rich in potassium, calcium and other minerals as well as nutrients such as phosphorus, lime and iron. But can ashes be used as fertilizer just like that? This guide provides information on this.

Not all ashes can be used as fertilizer

At the beginning of the last century, researchers and scientists wondered why the soil around a charcoal factory was often so fertile. This ancient craft was about making charcoal, with the leftover ashes simply being disposed of on the surrounding grounds. With the advent of artificial fertilizers after the Second World War, interest in researching possible connections between wood ash and the fertility of the soil waned. Since the question of biological fertilizers is very topical today, it has been taken up again and examined more closely. The result was the realization that, under certain conditions, ash helps plants thrive more abundantly. Basically, coal ash is unsuitable as an organic garden fertilizer. This mostly contains highly toxic heavy metals, like lead or chromium, as well as harmful phosphates. Wood ash, on the other hand, is very well suited as a fertilizer in private kitchen and ornamental gardens on a small scale if it meets the following requirements:

  • only untreated wood
  • no lacquered wood
  • no wooden furniture
  • black and white newspaper to light up
  • no catalog pages to ignite
  • do not mix coal with wood ash

If wood was burned to ashes in the fireplace, the origin of which is unknown, it should not be used as a fertilizer. For example, if it came from the vegetation on the edge of a motorway, it can be heavily polluted with toxic residues from car exhaust. If, on the other hand, it is unmistakably clear that it comes from sustainable cultivation or from your own garden, the ash is an environmentally friendly natural fertilizer. Only black and white newspaper should be used to light the fireplace, because the printing ink consists only of soot particles. In the case of colorfully printed papers, such as glossy brochures, chemical agents are used in the production process which, under certain circumstances, contaminate the entire ash and thus make it unsuitable for use as a natural fertilizer.

Wood ash is used as a fertilizer

If all the initial requirements for the pollutant-free wood ash are met, the hobby gardener can choose between two methods of application. The wood ash can be spread directly in the bed. A maximum of 30 grams per square meter should be spread over the floor; otherwise there is a risk of overfertilization. Alternatively, a thin layer of wood ash is occasionally put on the compost heap, alternating with other compostable materials. The possibility of using wood ash as a biological fertilizer only imperceptibly reduces the amount that has to be disposed of in the ash or garbage can. The disposal costs for chimney ash are therefore hardly reduced by using it as fertilizer. However, experienced hobby gardeners report a positive effect on the vigor of plants fertilized with wood ash,

These plants can tolerate manure made from wood ash 

As the ashes from burned wood dissolve in a short time and penetrate the soil, the strengthening effect on the plants in the bed is remarkably effective. Since it is very basic, the ash neutralizes acidic soil, so that it is not suitable as a natural fertilizer for all plants. There is nothing against the use of wood ash in the following areas:

  • in the vegetable garden
  • under bushes
  • in the flower beds
  • an Obstgehölzen

In particular, the following fruit, vegetable and ornamental plants benefit from fertilization with wood ash:

  • leek
  • Brussels sprouts
  • Saddlery
  • potatoes
  • Green asparagus
  • tomatoes
  • Carrots
  • Onions
  • Grapevines
  • Gooseberries
  • Raspberries
  • Rosen
  • Geranien
  • Fuchsien
  • many flowering perennials

All types of plants that require acidic soil, such as:

  • Azaleen
  • Busy Lizzie
  • Rhododendron
  • Camels
  • Orchids
  • Daffodils
  • Peonies
  • Cranberries
  • Kiwis
  • Rosskastanien
  • Palm trees

Compensate for potassium deficiency with wood ash

If beetroot or potatoes do not want to thrive properly, are poorly harvesting, have tough leaves and have brown edges, then the cause may be a lack of potassium. This is rare with organically fertilized potting soil, but it can be triggered by a longer period of drought or if the plants are in bog or sandy soil. In this case, using wood ash as a fertilizer can help. However, the maximum dose of 30 grams per square meter must be observed. Alternatively, a little rock flour or compost can be added to the charcoal ashes. An insufficient supply of potassium can also trigger the dreaded rust disease in various plants, for example in pears, plums, peas, cloves, fuchsias, St. John’s wort, mallow and daisies. Since the spores of this fungal disease are spread by insects, a large part of the vegetable and ornamental garden is infected in no time at all. A sufficient supply of potassium is therefore essential for plant health. With ashes made from charcoal that meet the required requirements, the biologically oriented hobby gardener can protect his plants against this deficiency symptom right from the start.

In forestry, the natural nutrient cycle is closed

Hobby gardeners who manage their own small forest will appreciate the high lime content of wood ash, because it is at least 20% here. Many forest soils in Germany are too acidic. If wood ash is applied in a well-dosed manner, this serves to improve the soil in the long term. The acidification is reduced and the trees can take root again, so that their stability is increased. The state of Baden-Württemberg is showing how it is done in a big way. It is expected that other federal states will follow. Therefore, there is nothing to prevent private forest owners and gardening enthusiasts from following this example, especially when they light a fireplace at home.

Wood ash can do more than just fertilize

In addition to using wood ash as a natural fertilizer, environmentally conscious hobby gardeners use wood ash in numerous other areas:

As a weed killer

Mosses and algae
When terraces and stairs are in a damp and warm location, unsightly mosses and algae inevitably spread. They also do not stop at the occupation of greenhouse panes. To combat this unwanted green coating, simply sprinkle a thick layer of wood ash over it and pour boiling water over it.

Root weeds
They are omnipresent in the garden and their tenacity makes life difficult for the hobby gardener. Root weeds such as dandelions, horsetail, plantain or thistles are repeatedly sprinkled with wood ash in autumn to prevent them from growing again in the next spring.

Stopping sap from leaking
Numerous succulent plants in the garden make beautiful bouquets for the vase in the house. If, for example, some shoots of the milkweed are cut off for this purpose, the flow of the sap is immediately stopped when the cut is briefly immersed in wood ash.

For pest control

The up to 30 mm long larvae of the Kohlschnacke attack the roots of the vegetable plant. If wood ash is scattered around the stalk of the cabbage, this measure prevents the infestation or stops the binge eating.

Leaf beetles and earth fleas
The dark-colored pests start their mischief from June and usually develop several generations per season. They prefer to attack garden cress, Chinese cabbage, radishes or radishes. In addition to the well-known biological control methods, such as spraying nettle manure, scattering a thin layer of wood ash also helps to get rid of the beasts.

There are more than 800 types of these weak parasites, which hardly spare any plant species; from balcony and tub plants to many vegetable plants to numerous fruit trees. One of the many biological control methods is lightly pollinating the infected plants with wood ash.

painting Experienced organic gardeners protect their trees every year with a coat of paint against frost damage, but above all against pest infestation by codling moths, scale insects and a number of fungal diseases. The following recipe with a high proportion of wood ash simultaneously heals wounds in the bark and increases the fertility of the trees:

  • 500 g wood ash
  • 5kg clay
  • 3 kg of cow dung
  • 500 g rock or seaweed flour
  • 0.5 l of undiluted horsetail broth
  • 10 l of warm water

These ingredients are mixed well together to create a viscous pulp. With the help of a brush, the tree paint is applied to the dry trunk in November and February on a frost-free day. Buds should not come into contact with the wood ash pulp. Lichen and moss are removed beforehand.

Instead of road salt, use wood ash to make paths accessible in winter
If roads around the house and in the garden covered with ice and snow are made safe to walk again using road salt, this can cause considerable damage to the surrounding plants even after many years. The road salt that seeps into the ground is one of the most common causes of rotting leaves on shrubs and trees because it has a long half-life. With wood ash, the icy surface is cleared of the smooth surface a little more slowly, but the careful hobby gardener can be sure that the surrounding plants will not damage the surrounding plants in the long term.

Hobby gardeners who keep rising energy costs within limits by lighting their own chimney or stove, receive a useful fertilizer for their kitchen and ornamental garden with the ashes. However, there are some important prerequisites that must be observed so that charcoal as a fertilizer has a positive effect on the plants and does not harm them. Ash that remains after burning coal or briquettes is extremely unsuitable as a fertilizer because it contains toxic heavy metals. However, if the fireplace is burned exclusively with untreated wood from sustainable cultivation and black and white newspaper is used to ignite the fire, an ash can result that is not only useful as a fertilizer, but also in pest control, as a weed killer and even as a substitute for harmful road salt is used. Hobby gardeners who manage their own small forest complete the classic nutrient cycle here when they bring out the ashes of the burned wood here for the purpose of liming. Wood from sustainable cultivation, which provides warmth in the fireplace, can therefore make an important contribution to the natural supply of kitchen and ornamental gardens.

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