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Two rows of mulched raspberries, third row on the right unmulched

When mulching ( medium high German  mul , disintegrating earth ',' dust '; see Mull ) or mallets is in horticulture and agriculture of the small or large area covering the soil with unverrotteten organic materials ( mulch hereinafter). Mulching in agriculture or landscaping as well as horticulture on larger areas is also the mowing with simultaneous shredding of the mulched material by sickle or flail mulchers . Mulching is an important contribution to long-term soil fertility and soil quality .

Unverrottete organic materials which in waters sediment are as sludge deposits then referred to as Mudde (s).

Origin and meaning of the word

The word “mulch” used today is a contemporary borrowing (late 20th century) from English ( mulch , 'unrotted organic material').

However, there is also an adjective mulsch , which has been used since the 16th century , which means 'rotten', 'soft' in some Upper German dialects (also in the form mölsch, molsch, melsch ). The root of the word is derived from the same root as “grind” and “mild” (cf. French mou / molle , Greek μαλακός malakos “soft” and Heth. Malisku- “weak, slightly“ insignificant ”).

The technical definition of mulch is "soil cover to promote the Gare".

C / N ratio

Mulch will sooner or later biodegrade, it will decompose and thus serve as fertilizer. When selecting the materials, it is important to ensure a balanced ratio of carbon and nitrogen ( C / N ratio ). If the C / N ratio is above 25: 1, the decomposition activity by microorganisms is inhibited because there is not enough nitrogen available for protein formation.

In the case of bark mulch, which has a C / N ratio greater than 60: 1, it is important to apply nitrogen balance fertilization before spreading . This necessity is based on the following processes: Nitrogen is one of the main nutrients for plants. Bark mulch is high in carbon, low in nitrogen and difficult to decompose. Therefore, in the initial phase, the soil organisms themselves use a lot of the little nitrogen available (from nitrogen fixation in the air) to break down the mulch. They build it into their body mass in order to grow ( building metabolism ). So little is available for the plants. This fixing of inorganic nitrogen to organic nitrogen compounds is called nitrogen immobilization . It counteracts nitrogen mineralization (nitrogen fixation, nitrogen utilization ).

The nitrogen immobilization and thus the nitrogen deficiency in the cultivated plants is temporary: once the breakdown process has started, nitrogen is slowly broken down and the nitrogen balance is equalized again. When the microorganisms ultimately die, they themselves become a source of nitrogen. The bound nitrogen is released again in the long term when the organic substances are broken down.

So that the plants do not suffer from a lack of nutrients as a result, the nitrogen must be supplied from outside. In perennial plantings, quantities of 50 to 80 g horn shavings per square meter have proven effective . Only after this slow and sustained organic fertilizer has been distributed is the bark mulch cover applied to a thickness of 5 to 8 cm. It is also beneficial to pre-compost hard-to-decompose litter. The more mature the compost, the lower the risk of nitrogen immobilization.

If, on the other hand, there is an excess of nitrogen, the C / N ratio is too narrow and ammonia can form, which also shifts the pH value unfavorably for the degradation. If this is the case, z. B. straw or sawdust are added.

Mulching in horticulture

Bark mulch (10 to 40 mm; pine)
Grass clippings months after application
Comfrey , also contains calcium

Mulching is an important technique in the context of row mixed culture and permaculture .

In horticulture , mulching is a special method that is used in the garden, in parks and when growing fruit and vegetables. The open ground between vegetable plants, flowers, bushes and trees is covered with lawn clippings, leaves , foliage and the like.


  • Protection: Mulch keeps the soil cooler longer when it is hot and keeps the daytime warmth longer in the evening. This extends the growing season. The moisture loss from the soil is also reduced. In heavy rain, the mulch layer prevents silting up and washing out of the soil, and in windy wind erosion .
  • Nutrient input: In addition to its protective function, the mulch layer is gradually composted and the resulting humus acts as an organic fertilizer . Earthworms and other small organisms bring the mulch material into deeper soil layers and convert it into valuable plant food. As with any composting process, it is important to have a balanced C / N ratio, see above.
  • Weed control: Due to the low incidence of light on the ground, weed growth on the covered area is slowed down, but not always prevented.


The right material is selected based on the nature of the soil, the vegetation, availability and the desired mulching function. If the mulch is removed when sowing cucumbers, the carbon / nitrogen ratio, for example, does not matter. Mulch on a playground is supposed to be soft but not dissolve as quickly.

  • Green waste: contains nitrogen, moist material can rot, can be easily combined with carbonaceous material such as straw, leaves. Weeds and plant debris can contain unwanted seeds or fungi.
  • Manure, compost: containing nitrogen, for mixing. Ripe compost is actually no longer mulch, it is finished humus.
  • Straw, leaves: carbonaceous, pure for woody plants and trees. Straw can contain pesticides and the like. contain, leaves from the street can contain heavy metals.
  • Bark mulch: contains carbon. Bark mulch made from shredded bark from conifers, mostly spruce , is also used in shrub beds and under bushes . The material should be long enough, i.e. H. Be deposited for at least three months to ensure that the phytotoxically active ingredients of the bark and tree resin such as tannins and tannins have already been broken down.
  • Sawdust: very carbonaceous, difficult to decompose
  • natural inorganic material: gravel or crushed stone is suitable v. a. for ways. Rock flour and lime are only used for fertilization.
  • Artificial material: In vegetable crops and under potted and container plants, biodegradable plastic and various types of conventional plastic sheeting are used for mulching - in the figurative sense of covering . The loss of moisture is very small, but the soil is hardly ventilated either. Black foils allow the sun to warm up. Nonwovens offer more air circulation, but are more translucent.


  • A Mulchbeet can badly chopped to ablate without the mulch layer.
  • Especially on heavy, loamy soils, it hinders warming from the sun.
  • Another undesirable side effect of mulching is that the organic garden waste can promote snail infestation, especially with dense, moist mulch such as fresh grass clippings.
  • The mulching of embankments, creek banks, road surfaces or meadows is criticized because it would also destroy insects, caterpillars, snails, small creatures such as frogs, snakes, lizards, and ground-breeding birds. By leaving the mulch material lying around, the soil is slowly over-fertilized and the diversity of flora and fauna is lost.

Mulching in agriculture

This sickle mulcher also mows and shreds woody cuttings with rotor blades lying on top of each other (hanging down here)
A ride-on flail mulcher that is used for extensive maintenance of green spaces, growth of up to 1.5 meters, undergrowth and young saplings
A hand-held flail mower that can be fitted with steel wheels so that it retains traction when it is very steep

In agriculture or large-scale gardening as well as in landscape management , mulching also means mowing with simultaneous shredding of the mulched material. Sickle or flail mulchers are used for this, which are available in various designs for front, mid- axle and rear attachment for tractors or single-axle tractors .

The advantage over mowing is that it can also be used to cut off and chop coarser and lignified plants. The mulch remains - as finely divided as possible - on the surface and rots there much faster than long-handled cuttings. For example, mulching is a substitute for landscaping where mowing or grazing are not possible, e.g. B. because the vegetation is unusable for fodder production , or the disposal of the crop would be too expensive. Mulching is part of the fallow land economy.

Since 2005, the prerequisite for receiving agricultural EU subsidies has been that arable and grassland areas that have fallen out of use are kept open by the subsidy recipient (farm) through mulching (in the case of grassland also mowing with clearing every two years), i.e. protected from encroachment become. The aim is to ensure that agricultural areas that cannot be cultivated profitably not only remain cultivable, but also improve the quality of their soil. Robust ride-on flail mowers or hand-held devices are used in particular for steep areas that cannot be worked with tractors and large agricultural machines or whose area is manageable.

In the attempts to keep open the state of Baden-Württemberg, the effects of mulching grassland areas on various locations as a landscape conservation measure have been examined since 1975 and compared with the development in undisturbed succession.


The machines used lead to the death of many insects and small animals. Mowing with the bar mower is gentler. In addition, mulching (in contrast to mowing with clearing) leads to nutrient enrichment, which displaces many flowering plants ( mesophilic plants ) that are dependent on poor locations .


Web links

Commons : Mulch  - collection of pictures, videos and audio files

Individual evidence

  1. ecology. P. 608 ( limited preview in Google Book search).
  2. Philip Schoenfeld: Organic mulch - step by step ; Surface manager magazine 1/2014 ( PDF file )
  3. Eva Höhne: ( Page no longer available , search in web archives: Development of a mechanistic model to simulate frost-related N2O emissions from soils ), p. 8, Martin Luther University Halle, 1981, accessed 2014.@1@ 2Template: Toter Link /
  4. Björn König: Investigations into the material use of extracted spruce bark. Cuvillier Verlag, Göttingen, 2008, ISBN 978-3-86727-615-3 , p. 41 ( , accessed 2014).
  5. Hans Joachim Fiedler: Soils and soil functions in ecosystems, landscapes and urban areas , expert verlag, Renningen 2001, ISBN 3-8169-1875-1 , p. 286, accessed 2014.
  6. JG Fuchs, J. Mayer and A. Berner: Influence of compost and digestate on plant growth and health: Potential and limits in values ​​- ways - effects: Organic farming in the field of tension between food security, market and climate change , Verlag Dr. Köster, Berlin 2009, ISBN 978-3-03736-033-0 , p. 26ff, accessed 2014.
  7. Dettmer Grünefeld: The mulch book: Practice of soil cover in the garden. 2010, ISBN 978-3-89566-218-8 .
  8. Friedrich Buer: Mulchmower - with public money and technology against biodiversity. ( , October 16, 2016).
  9. The attempts to keep the state of Baden-Württemberg open. , LEL Schwäbisch Gmünd.
  10. ↑ Bee pasture catalog - improvement of bee pasture and species protection , Ministry for Rural Areas and Consumer Protection Baden-Württemberg , accessed on June 22, 2018