Does Mulching Protect The Soil?

Last updated on October 23rd, 2023 at 08:24 pm

A magic word for organic vegetable and herb gardening is mulching. I am an enthusiastic supporter of this method, because mulching is an extremely sensible measure to protect the soil. It is a pity that this practice is rather rare in European gardens. The model for mulching is nature, where there is usually no bare soil except in extreme locations. Nature always strives to cover the fertile soil with vegetation. Mulching is therefore nothing more than providing the soil with a protective material. Since soil organisms break down the mulch material into nutrients, it can be described as a kind of surface composting.

Mulching – this is how it is done

The mulch material is only spread on freshly prepared, weed-free beds. The soil remains covered with a 5-6 cm layer of mulch all year round, which is always replenished as soon as it has rotted. Fresh, succulent material is only applied in a thin layer, preferably on a sunny day. After wilting, another layer can follow. It is better if the material has already wilted somewhat when it is spread. For sowing and planting, you can simply push the mulch layer aside a little. When the plants are bigger, the mulch layer can be pushed directly to the plants again. In the resting phase from autumn to spring, the mulch layer on the beds can also be thicker.

What materials are suitable for mulching?

Does Mulching Protect The Soil?

Suitable organic mulch materials are plentiful: straw, hedge trimmings, hay, lawn clippings, leaves, sawdust, bark mulch, rotted compost. The mulch material should be shredded so that it is easier to spread around the plants and decomposes more easily. It is certainly advantageous to mix different mulch materials; for example, chopped straw ensures that the fresh lawn cuttings do not clump together and rot.

There are also gardeners who use paper or cardboard. In principle, these materials are also organic; however, they decompose very slowly and probably not without harmful residues. They often contain dyes that are not always free of harmful substances. There is also the aspect of aesthetics, because a bed mulched with paper or cardboard is somewhat reminiscent of a rubbish dump.
Better: Do without mulch films

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Mulching with organic materials has not yet been able to establish itself in European gardens. Perhaps this is because it contradicts the conventional image of a clean and tidy garden. Black mulch films are more commonly seen in arable farming. Although they provide rapid soil warming in spring, they do not nourish soil life, do not let moisture out and suppress air circulation. From an ecological point of view, there is also the problem of disposal.

What is mulching good for?

Mulching brings us a number of incredible benefits compared to traditional soil care, plus it saves time and money. Under a mulch cover, soil life remains protected and develops magnificently. The mulch is slowly decomposed by numerous living organisms into valuable humus. The soil life is fed from above, so to speak. This means that less fertiliser needs to be applied, because the activated soil life provides the cultivated plants with many nutrients. Soil fertility improves considerably. The earthworms are also encouraged and in return they root through and loosen the soil for us.

Less watering and never more hoeing

The mulch cover protects the soil from great heat and cold, but also from strong winds and downpours. Hardening, dry cracks, silting and drying out are thus prevented. Herbs and lettuces stay clean because they are not soiled by soil splashing up when it rains. The soil remains loose and moist under the mulch layer without crusting. In dry summers, this can save a lot of water. Watering is reduced to a minimum because the soil moisture is retained for an exceptionally long time under the mulch layer.

A positive side effect of mulching is the reduced susceptibility to disease, because there are fewer fungal diseases in the loose, airy soil. Pests, such as earth fleas, are also driven away by mulch.

The greatest advantage of mulching, however, is the suppression of so-called weeds. There is no need for hoeing and weeding; you can easily pluck out the few wild weeds that nevertheless fight their way through the mulch. They are then simply left lying on the mulch cover. This leaves the gardener more time for the hammock!

Advantages of mulching at a glance

Water saving effect
Lower frost depths
Protection against silting, crusting and erosion
Promotion of soil life and soil fertility
Suppression of "weeds
Balanced soil climate
Reduced nutrient leaching
Fertilising effect
Protection of the roots from injury, as hoeing is no longer necessary
Clean herbs at harvest
Reduced susceptibility to disease

A little mulching knowledge

In organic gardening, you should only use organic materials for mulching. However, not all of them can be recommended without reservation:

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Bark mulch is unsuitable in most cases (pH 4-5) because of the growth-inhibiting tannins and the unfavourable acidic pH value. At most, it is useful for garden paths to suppress weeds and for some ornamental shrubs that love acidic soils (azaleas, rhododendrons, ferns, hydrangeas). Bark mulch removes a lot of nitrogen from the soil when it rots (nitrogen fixation!), which the plants then lack. Therefore, it should be enriched with nitrogenous material (e.g. horn meal).

Better than bark mulch is the bark humus obtained from it. This is composted bark mulch. Composting removes the growth-inhibiting substances. Plants that love acidic soils can be provided with it without any problems. For most medicinal herbs, however, bark humus would need to be limed up to improve the acidic pH (4.5-5.5).

Peat has no nutrients, also acidifies the soil (pH 4) and thus hinders soil life. Added to this is the fact that peat bogs are increasingly rare habitats whose destruction we do not want to encourage.

Similar to bark mulch, foliage releases tannic acids that have a negative effect on the growth of garden plants. Not all types of foliage are unsuitable; for example, foliage from fruit trees can be used very well as an admixture. Under no circumstances should you use foliage from elder, oak, beech, walnut, chestnut and conifers. These leaves must first be composted because of the growth-inhibiting substances. Then you can use it as mulch without any problems.

Straw is a very good mulch material, especially if it has been chopped up. If possible, only use straw from organic farming. Contrary to popular belief, it hardly removes any nitrogen from the soil as it decomposes. Nevertheless, it is helpful to mix some organic nitrogen fertiliser into the straw mulch to speed up decomposition. Dousing with nettle manure is a tried and tested method.

Sawdust is also suitable as a mulch layer and, like straw, is enriched with some nitrogen fertiliser.

Meadow and lawn cuttings are the best mulch materials. Mown green manure, weeded weeds or wild herbs such as nettle and comfrey are also excellent. When they are very fresh, they are only applied thinly to prevent rotting. It is best to mulch on a sunny day so that the covering can dry right away.

You can also make silage from grass clippings. This is done by lactic fermentation. The advantage is that slugs do not like silage.

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Non-organic mulch materials

Lava granulate is not only helpful against soil compaction, but is also very suitable as a heat-retaining mulch layer for southern plants on herb walls and in planters. Unlike the other (organic) mulch materials, it is a mineral base material.

You can also use shells as mineral mulch.

Different mulch materials and their special features

Mulching materialsSpecial features
Bark mulchAcidic, growth inhibiting
Bark humus/compostAcidic
PeatAcidic, low in nutrients, valuable habitats
FoliagePartly acidic and rich in tannins
Strawdoes not attract snails
Grass and lawn clippingsA perfect mulch when a little dried out
Grass silagedoes not attract snails
SawdustPartly acidic and rich in tannins
Lava granulate/ shells, pumicenon-organic, good for Mediterranean herbs

Problems with mulching

However, the mulch layer not only promotes beneficial soil organisms, it can also attract unwanted garden visitors.

In slug-rich gardens, damp mulch is an ideal biotope for the slimy gourmands, who can carry out their raids on the tasty little garden plants from this hiding place. Especially fresh and slightly wilted material attracts slugs, which is why only dry material should be mulched in endangered “slug gardens”. Mulch made of straw and sawdust is not very popular with slugs. Grass silage is also a mulch material that slugs avoid. The initially unpleasant smell of silage quickly disappears.

Thick layers of mulch can also attract voles. In this case, you should definitely mulch thinner, especially in winter.

Mulching is an ideal method of weed control, but only if there are not vast quantities of wild weed seeds in the mulch material. Therefore, especially with meadow cuttings, care must be taken that not too many grasses and herbs have flowered. Otherwise the seeds will be carried around the garden.

In larger areas it can be quite difficult to obtain enough mulch, because the soil organisms work diligently and the mulch layer needs constant renewal.


  • 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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