Mulches

Mulches are materials that cover the ground, much like layers of leaves on the forest floor. Mulches improve water retention, reduce erosion, moderate the temperature of the soil, reduce competition from weeds, and bring added nutrients to the soil while also helping to retain existing nutrients.

Many farms use plastic mulches, though there are environmental issues related to their production and disposal. Organic mulches such as hay, straw and leaf mould can decompose in place, providing nourishment for the soil food web which in turn provides nourishment to the plants. In fact, a heavy layer of nutrient-rich mulch can be used as the primary fertility-building method in veganic growing (such as the Ruth Stout technique). Mulching is especially compatible with no-till techniques, and mulches can be added in layers, known as sheet mulching or lasagna gardening. Mulching can ultimately result in a low-maintenance system, with a reduced need to water, weed, or fertilize.

Below are the advantages and disadvantages of mulching, suggestions for mulch materials, basic guidelines for applying and planting through a mulch, the use of mulches to begin a new garden patch, the use of mulches in mechanized agriculture, and the use of mulches in pathways and weed-infested areas.

Advantages of mulching

Reduces erosion and helps retain soil nutrients: Wind, rain and melting snow can lead to soil erosion and cause a loss of nutrients through run-off. By providing a protective layer between the soil and the elements, mulch helps retain existing soil nutrients and a healthy soil structure.

Feeds the soil food web: Healthy soil contains an array of organisms, including worms, fungi, and thousands of species of microorganisms. To keep the soil organisms alive and well, they must be provided with organic material to feed on. By mulching with organic materials, such as hay and leaves, this provides the soil organisms with a slow and steady supply of nourishment. The microorganisms will decompose the mulch materials, making the nutrients available to growing plants.

Reduces growth of competing plants: A thick layer of mulch substantially blocks the sunlight from reaching the soil. This inhibits underlying seeds from germinating or young plants from growing, leading to fewer weeds. To ensure that the plants you grow have proper access to sunlight, the mulch can be pushed aside in areas where seeds are sown or young plants are transplanted.

Improved water retention: Mulches add an extra layer between the soil and the sun, reducing evaporation and helping to retain water. The need to water is considerably reduced or eliminated, and the plants experience more consistent levels of moisture.

Moderates soil temperature: The temperature of the soil changes over the course of the season, during cold snaps and heat waves, and also from daytime to nighttime. Mulches provide a layer of insulation, keeping soil temperatures more moderate.

Protects perennials and biennials during the winter: The mulch will help retain snow, which creates insulation for over-wintering plants.

Reduces soil compaction: The mulch acts as a protective mat over the ground, reducing compaction from footsteps or heavy rainstorms.

Disadvantages of mulching

Excess moisture: In areas of a farm or garden that are already too humid, the moisture-retaining qualities of mulch could prove to be a drawback. As mulches retain moisture and create shade, this can provide a habitat for slugs and may result in crop damage.

Weed seeds and perennial weeds: When hay is used as a mulch it can contain weed seeds. Normally this doesn’t pose a large problem as the mulch also inhibits weeds. Tillage increases issues with weed seeds, so consider no-till techniques.

Perennial weeds can become established in mulched no-till gardens, so we must be mindful of removing these plants or cutting them down before they go to seed.

Cooler soils in spring: In the springtime, mulched soils may take longer to heat up since they are not directly in the sun. However, mulches also help create a vibrant living soil, which in itself produces a certain amount of heat.

Limitations with machinery: Mulching is more limited with mechanized agriculture, though certain techniques are described later in this article.

Suggestions for mulch materials

Veganic agriculture encourages the use of locally-available materials, especially those produced on our own land. The following is an inexhaustive list of potential mulch materials. Keep in mind that any plant material can be used as a mulch, including crop residues like leaves, stalks, and corn husks. Weeds can also be used as mulch, though avoid weeds that have gone to seed.

- Hay: Hay is high in nutrients and is available locally in many regions. Hay can form the primary fertility technique in veganic growing (the Ruth Stout technique). Rather than passing the hay through a cow and using the resulting manure as a fertilizer, the hay itself is a whole-foods resource that can be fed directly to the organisms in the soil.

- Straw: Straw is lower in nutrients, though is often cheaper and readily available, and should not contain weed seeds. Strawbales and haybales are often used as decorations at Hallowe’en (by schools, supermarkets, etc.). Try to obtain these valuable resources before they are tossed out, and store them to use as mulch the following spring.

- Chipped Branch Wood: Chipped Branch Wood, made from deciduous branches less than 7 cm in diameter, can be used as an effective mulch. The lignans are broken done slowly by fungal activity, resulting in a stable humus similar to that of a forest. Please note that Chipped Branch Wood is different in nature than the woodchips that are commonly used as mulch material (woodchips made from large branches or trunks have an imbalanced carbon/nitrogen ratio, and can cause nitrogen lock-up for years if mixed with the soil).

- Cardboard: Cardboard is lower in nutrients, though is easily accessible and simple to spread in sheets at the beginning of the season, and is phenomenal for weed suppression. Cardboard can be covered in another layer of mulching material, such as hay.

- Newspaper: Lower in nutrients, though easily accessible. Use only black-and-white, non-glossy newspaper.

- Grass clippings: Use in moderation.

- Leaf mould: Leaves are more appropriate for mulch if they are allowed to break down for a few months in advance. Many people throw out this resource in the autumn. Collect bags of leaves from your neighbors or offer to rake their leaves for them. Favor areas that are uncontaminated by dog feces and away from the pollutants of busy roadways.

- Green manures / cover crops: Green manures and cover crops are typically incorporated with the soil after being cut down, though alternately they can be left on the surface of the soil as a mulch. Depending on the green manure selected, they can help bring significant nitrogen and biomass.

- Living mulch: Living mulches keep the soil covered with living plants, which, like other mulches, helps to protect soil that would otherwise be bare. For example, between rows of vegetables, the pathways can be planted with a living mulch of dwarf white clover.

- Meadow clippings: Plants that are trimmed from a meadow can work well as a mulch, as done by German veganic farmer Kurt Kretschman.

- Comfrey: Comfrey plants have a long taproot, bringing up nutrients from deep within the soil. The nutrient-dense leaves of the comfrey plant can be used as a mulch. A patch of comfrey can be planted for this purpose, though foresight is needed when planting comfrey, as established plants are almost impossible to remove.

- Seaweed: Seaweed can be used as a mulch, though we must be wary of potential contaminants in the water supply, and high levels of salt can burn the plant roots.

- Regionally-specific mulch materials: Look in your local region for uncontaminated plant matter that could be used as a mulch. There is often the possibility of diverting materials from the waste stream, such as spent hops from breweries, buckwheat hulls, or shells from the nut industry.

Basic Guidelines for applying a mulch and planting through it

The thickness of the mulch you apply will depend partly on the material you choose and the quantity you have available. Even light applications of organic material can provide nourishment for the soil food web, though to experience the full benefits of mulching—soil protection, water retention, reduced weeding—a thick blanket of mulch material should be spread on the soil. Aim for at least 2 inches (5cm) of mulch material spread evenly across the surface. In the case of hay and straw, which are light and airy, aim to add 6-10 inches (15-25cm) of material. Mulch can be added in the spring, and again in the fall if needed.

To plant through a mulch such as hay or straw, simply push the mulch aside to add seeds or transplants, making a small hole or row in the mulch in the areas where you’d like to grow. This allows the sun to penetrate specifically for the plants you are growing. If using a layer of cardboard as a mulch, the cardboard needs to be cut with a knife in the places you would like to plant.

Using mulches to begin a new garden

When beginning a new garden, often people use shovels or rototillers to remove the existing plants, though in doing so this disrupts the underlying soil structure and the organisms that live within the soil. Mulches present an alternative, allowing us to begin a new garden or farm field while leaving the soil completely intact. Mulching is also a “low-work” system, providing a way to garden without heavy digging or special machinery.

- If beginning a new garden on a lawn or a field, ideally start by cutting the existing plants (such as grass and dandelions) so they are relatively low.

- Cover the ground with a layer of mulch, so that light is unable to penetrate. Cardboard works well, as it completely blocks the sunlight from reaching the ground. Deprived of light, the plants underneath will cease to grow, and will eventually decompose to nourish the soil life.

- Ideally, cover the cardboard with another layer of mulch, an organic material such as hay, straw, or leaf mould. This will help bring fertility to the garden (especially hay, which in and of itself can be the main source of fertility in agriculture). Covering the cardboard also makes the garden more attractive in urban environments. These mulches can be used on their own to start a garden, without any cardboard, though a thick layer, such as 6-10 inches (15-25cm) of hay or straw, is needed to inhibit the sunlight.

- Plant through the mulch. In the first year, potatoes are a good choice since they are hearty and help decompact the soil for future years. Find seed potatoes, or older potatoes that are growing eyes. Cut an X in the cardboard with an exacto-knife, and place a potato through the X directly onto the lawn, with the eye of the potato poking up through the X into the sunlight (note: potatoes do not need to be buried in the soil to grow successfully. If placed directly on the lawn, their root system will work its way into the soil. Potatoes simply need to be deprived of light, since exposure to light causes potatoes to become green and toxic. The cardboard and organic mulch can adequately block the sunlight, especially if a second layer is added mid-season). Continue to cut X’s and add potatoes, at a distance of about 1 foot or 30 centimeters between potatoes. In the late summer or early fall, when the leaves of the potato plants begin to look brown and dry, lift up the cardboard. There should be a crop of potatoes sitting on top of the soil, easy to harvest. At this point, the soil will also be prepared for growing a more diversified garden in future years. The underlying lawn will have decomposed into soil, and the roots of the potato plants will have made the soil lighter and airier.

- Alternately, you can plant a diversified garden using mulches in the first year of growing. Using ’lasagna gardening’ or ’sheet mulching’ techniques, several layers of different mulching materials are added directly to the lawn (or even on concrete), building a thick layer (approximately two feet) of organic material above the ground. Mulching materials include food scraps, compost, newspaper, cardboard, and leaves. If built up in the fall, a wide variety of plants can be grown directly in the mulch the following spring. More precise details can be found online, such as this lasagna gardening article (fully veganic if you skip the manure).

The use of mulches in mechanized agriculture

The use of mulches in large-scale mechanized agriculture can be more limited, due to the amount of mulch material needed and the potential incompatibility with the farm machinery. However, there are certain options for mulching on a farm.

In terms of finding enough organic material to mulch with, this can be produced on the farmland, bringing the potential to fertilize the fields without buying inputs. It is not uncommon for farmers to sell their hay and purchase manure. When hay is passed through an animal to create manure, much of the nutrients, such as calcium, are used up by the animals’ bodies. Instead, a closed loop of fertility can be created on the farmland, by using the hay as a mulch to fertilize the plants. When using hay for fertility, this is a more direct source of nutrients without any losses.

There are also techniques for applying mulches with large-scale farm machinery, with mulch materials that are grown directly in the fields. A straw-grinder can be used to grind the straw directly in the rows. Or a roller can be used to knock down rye, creating a mat that rests on the surface of the soil as a mulch. Soybeans or corn can then be planted through the rye with no-till seeders and transplanters. The Rodale Institute has been experimenting rye as a mulch. More information can be found at The Rodale Institute, Midwest Organic and Sustainable Education Services, and the National Sustainable Agriculture Information Services.

Many farms use biodegradable plastic mulches. While this does not nourish the soil, it does bring some of the advantages of mulching, such as weed suppression and water retention, and it also warms the soil.

The use of mulch in pathways or in areas infested by weeds

Mulch can also be used in the pathways of gardens and farm fields, generally with the aim of inhibiting weed growth between rows of crops. An inexpensive and lower-nutrient mulch, such as straw, can be used in pathways. This can be used in conjunction with a high-nutrient mulch, such as hay, added in the rows of plants.

Living mulches can also be used in pathways to inhibit weeds and maintain a healthy soil. The Langerhorst Family in Austria plants dwarf white clover in their pathways, and they walk on the clover as they do their farming.

In areas that are already infested by weeds, mulches can be used to suppress these weeds and inhibit further growth, such as using a thick layer of cardboard. Please visit the website of Plants for a Future for a detailed explanation of the technique (see “mulching weed-infested sites”).


18 April 2011
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