K11

Gardening without Peat

Peatbogs: carnivorous plants, amazing archives and carbon "sponges"

Each year in the UK, around 2.5 million cubic metres of peat are sold to commercial and amateur gardeners. In Great Britain, over 94% of the 69,700 ha of peatbogs have been damaged or destroyed. Most of this damage has occurred in the last 50 or so years, since the promotion of large-scale use of peat for the horticultural industry.

Peatbogs are important sites for wildlife. They are unique habitats which support a fascinating variety of birds, invertebrates and plants. Carnivorous plants such as sundews (Drosera species) thrive in these low-nutrient ecosystems. They trap insects and digest them to supplement their food supply.

Peat is partially decomposed plant debris, and can include trees, shrubs, herbs, sedges, grasses and mosses. Peat forms where plant debris is added faster than it is broken down. In cool, waterlogged conditions, the lack of oxygen and low temperatures limit the rate at which micro-organisms degrade plant material. In places the peat can be many metres deep. The lowest layers of peat can be thousands of years old. Peat preserves trapped plant remains, pollen, human artefacts and even bodies such as "Pete Marsh", the 2,300 year-old Lindow Man in Cheshire. To scientists and archeologists these natural archives can reveal stories of past civilizations, botanical history and climate change.

Peatbogs also help to protect the earth from global warming. As plants grow they absorb carbon dioxide. It is 'locked up' within the plant structure, and stored as the plants turn to peat. When peatlands are drained or disturbed, the peat starts to decompose. The carbon dioxide is released back into the atmosphere where it acts as a potent greenhouse gas.

Uses of peat and alternatives

Peat is used in horticulture either as a soil improver or as a growing medium. Traditional methods, many relying on waste organic matter, together with the neweer peat alternatives can give equally good, if not bettr results without damaging a valuable habitat.

Mires, bogs and fens

Mires refer to all types of peatland, including bogs and fens.

Fens are chemically neutral and fed by drainage water, while bogs are made of acid peat, with moisture supplied exclusively or predominantly from rainwater.

Raised bogs have a characteristic dome due to the build-up of organic material.

Lowland raised bogs are the most seriously threatened habitat, but conservation of blanket bogs, fens and other peatlands is equally important.

What is compost?

Composting is the breakdown of degradable organic matter by microbes under moist, warm, aerobic (in the presence of oxygen) conditions. Waste plant material, kitchen scraps and manure are common ingredients. The resulting compost is a stable, odourless material. It contains valuable slow-release nutrients and has a structure which improves soil water-holding capacity and drainage.

The word "compost" is also used to describe a range of products (usually growing media) on sale to gardeners. Most have not been composted, but are simple mixtures of substances such as peat, sand, coir and loam.

"Potting composts"

Growing media (often called "potting composts") are used for plants which are grown in containers such as tubs and window boxes. The most popular alternative to peat as a growing medium is coir (pronounced "koya"). Coir is the protective fibrous layer surrounding the hard shell in coconut fruits (Cocos nucifera). The fibres are used to make ropes and mats. During the fibre stripping process, the pulp surrounding the coir fibres is removed as a waste material. In Sri Lanka, western India, the Philippines and other areas where coir is produced, this residue causes considerable disposal problems and is generally left in piles, occupying valuable land.

The residue is a crumbly brown substance. It is used in potting media as a bulk ingredient to increase moisture retention and porosity. Staff at Kew have found it to be suitable for bedding plants, germinating seeds and for propagation of cuttings, though in some cases the fertilizer or watering regime has to be modified carefully.

Soil improvers

Soil improvers are used to alter the soil structure, water-holding capacity, nutrient content, acidity or conditions for other organisms (such as earthworms). Any bulky organic material can be used to improve the organic content of soil. Garden compost and leafmould are among the best materials for enriching soil, but bark products and manure can also be used. Low in nutrients and quite difficult to work into the soil, peat does not make a good soil improver.

Kew has always used a wide range of organic materials in its horticultural work. We have one of the largest compost heaps in the UK, and recycle 99% of our plant waste. This plant material is mixed with horse manure, and the resulting compost is dug into the soil to improve the texture and nutrient content of Kew's naturally very poor and sandy soil.

Mulches

Mulches are layered on to the soil surface to suppress weeds, conserve moisture, improve its visual appearance and minimize erosion. Peat is a poor mulch as it tends to dry out and blow away. Alternative mulches include organic materials such as animal manure, leafmould, bark chippings and composted garden waste. Another useful "peat alternative" mulch is cocoa-shell, the crushed shells of cocoa beans (Theobroma cacao) which are a by-product of the chocolate industry. Kew uses mulches of compost, chipped bark, and shredded prunings.

Kew also uses inorganic mulches including pebbles (near the southern entrance to the Princess of Wales Conservatory), sand and gravel (Rock Garden). Other inorganic mulches such as blanket mulches, polythene sheets, carpet, newspapers and cardboard can be used where appearance is less important.

Some plants such as rhododendrons require acid soils. Pine needles and composted heather and bracken can be used as mulches to increase the soil acidity, as alternatives to peat. At both Wakehurst and Kew, bracken compost is collected from local nature reserves (where invading bracken threatens other species).

How can you help to protect peatbogs?

Don't buy peat in any form
Peat-free "multi-purpose composts" include coir-based mixtures, but ask your garden centre for advice. Also, avoid buying container-grown plants in a peat-based medium. Always ask when buying; outlets will respond to consumer pressure.

Compost! Make your own
It is free and reduces the amount of waste sent to landfill sites.
Using peat is unnecessary as there are now successful alternatives for use by both amateur gardeners and commercial horticulturists. Gardening without peat helps to make better use of waste organic materials while helping to conserve what is left of the unique and valuable habitat of the peatbogs.

Further information

Out of the Mire (1992) RSPB and Plantlife, Sandy, Beds.

Gardening Without Peat: The Friends of the Earth guide to peat alternatives (1991) FoE, London.

Good books on composting are available from The Henry Doubleday Research Association, Ryton Organic Gardens, Coventry, CV8 3LG, UK. Tel. (01203) 303517.

Many local authorities now compost household waste, producing a good mulch or soil improver at a very reasonable price. Contact your local authority for further information.