Table of Content
What is Mulching?
Mulching means covering the soil with a protective layer. This layer can be made of very different materials: classically from organic matter such as leaves, grass clippings, compost, straw, bark, or wood chips, but also from mineral materials such as gravel, crushed stone, or lava rock. Increasingly, mulch films are also used – black, clear, or biodegradable foils that act like a second skin on the soil. Another unusual but very effective option is mulching with sheep’s wool or fleece. These materials decompose very slowly, retain warmth and moisture, and have the additional benefit of deterring slugs.
A special historical form is stone mulching. In arid regions, stones were spread thickly over fields. During the day, they stored heat, which they released at night, while at the same time reducing evaporation. Archaeological evidence shows that stone mulching was already used by the Inca in South America or in Mediterranean vineyards. In extremely dry climates, this technique made agriculture possible for centuries.
Mulching is therefore less an “invention” than a principle that developed wherever humans practiced agriculture. The underlying idea is simple and universal: soil should never be bare and unprotected, but always covered and enriched with organic or mineral materials.
Historical Roots – from Egypt to the Andes
People understood the value of soil cover very early on, as numerous historical sources show. In the oases of Egypt, palm leaves and straw were used to retain water. Greeks and Romans covered olive groves and vineyards with organic waste to keep soils fertile. In the Andes, farmers used lava rock as stone mulch to make poor soils more productive. In China, it was common practice to spread straw and rice husks on fields.
Mulching is therefore not the idea of a single person, but knowledge that grew over thousands of years. Different cultures found their own materials and methods, but the basic idea remained the same: protect the soil to make it more fertile and resilient.
Why Mulch?
The benefits of mulching are many. A mulch layer protects soil from drying out by reducing evaporation. It acts like insulation that regulates temperature – in summer the soil stays cooler and moister, in winter it remains frost-free longer. Rain cannot compact or erode the soil as easily. Weeds are suppressed because they germinate poorly under a dense cover.
Organic mulches also promote soil life. Earthworms, microorganisms, and fungi find food and habitat, improving soil structure and increasing humus content. A living soil, in turn, supplies nutrients to plants, improves water infiltration, and is more resilient to extreme weather.
Here in Cape Breton, Zone 6a, these advantages are especially noticeable. Summers are often windy and dry, winters harsh and cold. Mulching helps in both extremes: keeping the soil moist in summer and warmer in winter. Combined with methods such as biochar, mulching builds soil that stores water better and teems with life.
Where Mulching Works – and Where It Doesn’t
Mulching is almost always a good idea, but there are exceptions. It is particularly useful in vegetable and perennial beds, under shrubs and trees, on slopes, and anywhere soil tends to dry out or erode. Newly planted areas benefit the most, since weed competition is reduced and stress minimized.
On very heavy clay soils, however, caution is needed. Too thick a mulch layer can reduce aeration. Compacted mulch hampers air exchange, traps moisture in the lower layers, and encourages rot and fungal diseases. With trees, the mulch should never touch the trunk. Young trees with thin bark are especially prone to collar rot, but even older trees can suffer if moist mulch constantly rests against the trunk.
Materials Compared
Compost is slightly alkaline, raises pH a little, supports soil life, and supplies nutrients.
Leaves decompose relatively quickly and can acidify soil slightly. Shredded leaves are ideal to avoid matting.
Grass clippings are neutral to slightly alkaline. They provide nitrogen, decompose rapidly, but can rot if applied too thickly.
Bark mulch is acidic and should be left to weather, ideally for a year, before use. Fresh bark mulch can strongly acidify soil and contains tannins that inhibit plant growth. Aged bark mulch is gentler and safer.
Wood chips decompose slowly and bind nitrogen at first, but they retain moisture and improve soil structure over time.
Sheep’s wool is a special case. It acts like a dense, fibrous carpet, storing warmth and moisture, slowly releasing nutrients such as nitrogen and potassium, and providing a natural slug barrier.
Mineral mulches such as gravel or crushed stone are pH-neutral, durable, and visually stable. However, they hardly support soil life and can overheat in full sun.
Mulch films are popular in vegetable growing. They reliably suppress weeds and warm the soil. To plant, the films must be cut or perforated. Mold rarely forms beneath them because they regulate water flow and allow some aeration. The bigger issue is microplastic: when films age or tear, residues remain. Biodegradable versions sound promising but often don’t fully decompose in home gardens. Many only break down completely in industrial composting facilities.
In Europe, EN 13432 and OK compost industrial (TĂśV Austria) are common certifications.
In Canada, other standards apply. Especially relevant are ASTM D6400 and ASTM D6868 (for compostable plastics), confirmed by the BPI (Biodegradable Products Institute) seal. There is also the Canadian CAN/BNQ 0017-088 standard, based on ISO 17088. Canadian gardeners should look for BPI or BNQ certifications when buying mulch films. So far, however, there is no completely risk-free film without microplastic concerns.
When to Mulch
The best time to mulch is in spring, when soil is frost-free. This way, winter moisture is retained and early weeds are suppressed. In summer, mulching protects against heat and drought. In autumn, it serves as winter protection for sensitive plants. In midwinter, however, it is of little use since the soil is frozen.
Colored Mulch – Attractive but Risky
Colored mulches often use pigments such as iron oxides, which are considered harmless. Yet doubts remain whether all products are equally pure. The main risk lies in the base material: cheap recycled wood, sometimes from treated pallets or construction timber. These can contain heavy metals and chemicals such as chromium, copper, or arsenic.
Why is this especially common with colored mulch? Because it is marketed as decorative, manufacturers often use low-cost wood sources. With natural mulches the risk is lower, but it is still worth asking about origin and certifications.
Our Path to Mulching
When we first laid out our starter plots, we faced a question: leave the soil bare to warm in the sun, or cover it right away? Experience quickly taught us that bare soil in our climate dries out within hours. So we began mulching – just as we described in What is Homesteading?.
We loosened the soil, removed coarse stones, and cleared the beds. Then came the first mulch layer: wood chips from clearing our land, combined with grass clippings from the neighborhood. A year later we added compost to improve nutrient supply.
Now, each autumn after pruning, we wrap our beds in a new mulch layer to give plants a better chance of surviving the winter.
Summary: Mulching Done Right
Prepare soil: loosen, weed, keep moist
Choose material: organic for nutrients, mineral for durability, sheep’s wool as a special case
Layer thickness: 5–8 cm for beds, 7–10 cm around trees, always keep distance from trunks
Timing: spring for moisture, summer for heat protection, autumn for frost protection
Maintenance: check regularly, refill, loosen mulch if needed
Caution: avoid fresh bark mulch, overly thick layers, questionable colored mulches, and uncertified films
Quellen
– Wikipedia: Mulchen
– Plantura: Mulchen – Funktion, Vorteile, Materialien
– NABU Heidelberg: Mulchen im Naturgarten
– Natur im Garten: Mulchen Grundlagen (PDF)
– UF/IFAS: Is Colored Mulch Bad for the Environment?
– Innovations-Report: Gefärbter Mulch
– Penn State Extension: Mulch – Options and Risks
– TÜV Austria: OK compost Zertifizierung
– BPI: Certified Compostable
– CCME/BNQ: Canadian Compostability Standard
