Should I buy peat-free compost?
By Adele Dyer
Peat-free composts have been on sale for many years, but they can still cause headaches for gardeners. We look at the pros and cons of alternatives to peat.
Why should I reduce the amount of peat I use?
Peat bogs in Britain are an invaluable habitat for flora and fauna, supporting many rare and vulnerable native species not found anywhere else. When peat is harvested, the bog is drained and the peat is stripped off in layers over several years. Peat extraction causes extensive damage to bogs, which means this vital habitat can't naturally regenerate.
Peat accumulates at a rate of less than 2mm per year, and peat harvested now has taken thousands of years to establish. Harvesting removes around 20cm per year. Although some schemes are in place to restore bogs that have been harvested, their long-term success has yet to be proved.
In addition, peat stores large amounts of carbon-dioxide and methane that are released into the atmosphere when it is harvested.
As a result, the UK government has agreed with compost manufacturers that peat shouldn't be in composts for home gardeners after 2020 and in composts used by commercial growers after 2030. The pressure is therefore on compost manufacturers to come up with ways of reducing and eliminating peat from composts within a few year.
What are the alternatives to peat?
There are now a number of peat-free composts available, as well as a large number that have reduced peat, meaning they contain around 50-70% peat, with peat alternatives making up the rest of the compost.Materials such as green compost, coir, wood fibre and composted bark are now used in most composts. In our trials in the last few years, we have found some excellent peat-free composts that have won Best Buy awards. However, we have also come across some shockingly poor ones. To find out which these are, look at our full compost test results.
Peat-free compost ingredients
This is usually made from the green waste collected by local authorities from door-to-door collections or from municipal waste sites. This material is variable. In summer, green waste is largely made up of grass cuttings, and in winter it's mainly woody material. New standards have been introduced to try to ensure a more stable mix of these two extremes and to eliminate contamination with glass, stone and metal.
Green compost often suffers from high levels of chlorides, which can prevent plants from taking up the nitrogen needed for leafy green growth. It also often contains large amounts of potassium, which can cause calcium and magnesium deficiencies in the plant. As a result, fertilisers need to be carefully balanced to avoid problems.
Some manufacturers have now decided not to use any composted green waste in their composts, but are using wood fibre instead (see below). Other producers have altered where they source the materials for their green waste compost from. They are focusing instead on farming, brewing and carefully vetted landscapers to ensure a steady flow of less variable ingredients.
Coir is now widely used in commercial horticulture as a peat alternative. It's a fibrous material made from coconut husks and is milled to make a peat-like material for horticultural use, and how well the coir is treated and milled has a direct effect on the quality of the coir. Most of the coir production is in coastal areas of India and Sri Lanka.
It's widely described as being environmentally friendly as it's a naturally occurring product that would go to waste if it weren't used in composts. However, there are several issues, including the carbon cost of shipping it around the world and the amount of water needed to rinse salts from the coir, as it's produced in areas where clean water is scarce. There are also concerns over working conditions and pay for workers.
Wood fibre is generally made one of two ways. Some companies use a wetting and drying technique to convert wood chips into a light, fluffy material. The result is a little akin to putting a woolly jumper in a tumble drier: the fibres expand and split apart, making them better at holding air and allowing water to drain freely. Others use the shavings taken from lumber yards as timber is sawn into planks.
It's often added to composts and typically makes up no more than 20-30% of the total volume, as too much wood fibre can lock up nitrogen, leaving plants starved of this vital nutrient.
Composted bark is typically made from the bark of conifers felled for timber. It's mostly sourced in the UK and is a by-product that wouldn't be used otherwise. It's milled to small pieces and often mixed with wood fibre and coir to grow plants.
Caring for your plants using peat-free compost
Green compost suffers from several problems. It can rot down quite quickly, creating a compost that slumps, reduces in volume and becomes compacted. It also varies in how nutrient-rich it is - for example, it can release large amounts of nitrogen or very little, which makes feeding tricky. And finally it can stay quite wet, so it's worth watching your watering, especially in rainy weather.
Coir holds water well, but it doesn't hold it as evenly as peat. The surface can be dry, but there can still be a good amount of water held further down the pot. To avoid problems of over-watering, it's best to water little and often. Judging when to water again can be tricky, but it's best to pick up the pot where possible. Pots that need watering will be much lighter than pots that still contain a good amount of water. You will quickly learn to judge which need water and which do not.
It's also important not to compress coir when you plant. Instead of firming in, overfill the pot and then tap it a few times on the workbench to settle the material, then water to further settle the contents. You may have to hold cuttings, plug plants and seedlings close to the top of the pot while you do this to prevent them from being planted too deeply. Wrap your hand around the pot while you hold the young plant between your thumb and forefinger and then use your other hand to tap the pot on the bench.
Wood fibre can increase drainage in composts that can become wet, such as composted green waste. However, in hot weather, it's important to make sure that the wood fibre does not cause your pots to become too dry. Again, water little and often to manage water within the pot.
Composted bark makes quite an 'open' compost with good air spaces within the compost. However, this does mean that it doesn't hold water well and you need to water generously, especially when potting young plants. Check plants regularly to make sure they don't dry out.All composts have a small amount of fertiliser in them, but you need to add a controlled-release fertiliser to sustain your plants through a full growing season.