Organic Matter for the Garden

Introduction to Organic Matter for the Garden

Organic matter — bulky material of living origin — is an essential constituent of healthy, fertile soil, but one that is continuously being depleted. Soil-living creatures consume it, cultivation breaks it down and gardeners remove replacement supplies which, in nature, would go back into the soil. Thus, to maintain soil fertility, organic matter must be applied regularly.

organice matter for the garden The value of organic matter in the garden Soil structure Most organic matter improves the soil structure which, in turn, improves its fertility by making the plant foods it contains more available, as well as making it easier for roots to grow through the soil.

Plant foods

Some materials supply plant foods. Being of living origin, they can contain the major elements (nitrogen, phosphate and potash) and the minor and trace elements essential for plant growth. Nutrient analyses can be variable and are not necessarily a good measure of the value of the product. The rate at which the nutrients are available can vary from weeks to years, depending on how long it takes the soil life to decompose the material.

Soil health

Organic matter can help to keep soil pest and disease problems under control.

Other uses

Bulky organic materials can also be used to control weeds, as a mulch to keep the soil moist, and as an ingredient in growing media.

Processing before use

Bulky organic materials are usually composted or processed before use to make them easier to handle, stabilize the nutrients they contain, reduce toxins or make them more attractive.

Materials from non-organic sources should be stored for six months to allow a reduction in any chemical residues present. Those containing plant foods should be stored under cover to prevent the goodness being washed out.

Animal manures should never be used when fresh. In this state they contain freely available nitrogen compounds that can scorch plants, and both nitrogen and potassium may be in forms that are easily washed out by the rain, causing wastage and pollution. In well-rotted manures these compounds are stabilized.

Shredded conifer and other evergreen material should be stacked or composted before use to allow any toxic substances to decay or be driven off.


Bulky organic matter can be purchased or collected free from neighbours, farms, markets and other sources. Manures, composts, bark and other materials may also be purchased ready processed from garden shops. These may be easier to handle than unprocessed materials, but are likely to cost more.

Ideally, everything brought in should be organically grown. Buy products carrying a recognized organic symbol where possible, and avoid sources like intensive farms where contamination from pesticides, antibiotics and heavy metals is likely.

How to use bulky organic materials

Most materials can be dug into the ground or applied as a surface mulch. Certain materials which are high in carbon and low in nitrogen, including wood shavings, sawdust and wood chips, should only be used as a mulch because incorporating them into the soil could cause nitrogen robbery. Materials containing plant foods are best mixed into the top 15-20cm (6-8in) of the soil as this is where the plants’ feeding roots are at work.

How much to use

Nutrient-rich materials

Increase for greedy feeders and poor soils; decrease for the opposite. Do not overfeed for fear of causing unhealthy, lush growth, and pollution.

Low/no-nutrient materials

There is no rea limit to the quantity of these that may be used

When to apply it

Nutrient-rich materials

Only apply to growing plants or to land where planting is imminent, never on bare ground in autumn and winter.

Low/no-nutrient materials

These can be applied whenever soil conditions are suitable.

Processing Animal Manures

Straw manures

Much of the goodness comes from the animal urine, so make sure the straw is well soaked and that the manure has not been standing out in the rain, which rapidly washes out nitrogen and potassium.

Straw manures can be added to a compost heap or stacked alone and left to decompose for several months. If the manure is dry, water it as the stack is built. Tread it down to expel excess air and cover with polythene.

Shavings-based manures

Manure mixed with wood shavings rather than straw should be used with caution; the shavings can cause nitrogen robbery when mixed into the soil.

Only use this type of manure if the shavings are well-soaked in urine and/or you can add additional nitrogen, in the form of grass mowings, nettles or comfrey, for example.

Stack under cover until it is very well rotted — it should be a dark colour with individual shavings no longer distinct. This can take a year or two. When in doubt, use as a surface mulch only on permanent plantings. Do not apply to poor soil.

Poultry manures

These are very high in nitrogen, contained in the white “dab” on the droppings. Mix with straw and rot as above or use as a compost heap activator.

29. January 2011 by Dave Pinkney
Categories: Manures and Fertilisers, Organic Gardening, Soil Cultivation | Tags: , , | Comments Off on Organic Matter for the Garden


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