Peat was once seen as a cheap and plentiful material that gardeners found easy to use. However, peat harvesting releases huge amounts carbon dioxide into the atmosphere and the climate crisis has shown us we need to stop this.
The Committee on Climate Change estimates around 39 tonnes of carbon dioxide has been released from every hectare of lowland peat that has been drained and fertilised every year. It's clear that we won't reach net zero while peatland is still drained and the peat extracted. As a result, the government aims to ban the sale of peat to gardeners by mid-2024.
The good news is that coming ban has forced manufacturers to develop better peat-free composts and to make more of them. Our trials show that many peat-free composts are now as good, or better, than peat-based products. Although some cost more than peat composts, there is a good choice of low-cost options. Take a look at our to see how they compare.
Peat is an accumulation of partially decayed vegetation, created from sphagnum mosses growing in bogs. It accumulates at a rate of 1-2mm per year as the moss slowly decays in the permanently wet conditions, sealing in large amounts of carbon. In fact, undisturbed peat bogs are more effective carbon stores than forests. Supporters of peat say this makes it a sustainable and renewable material, but the problems start when we extract it.
To harvest it for use in compost, peat bogs are drained and cleared of all vegetation. Harvesting not only removes around 20cm layer of peat every year, in other words, a century’s worth of peat accumulation, but allows the exposed peat to oxide, releasing carbon dioxide.
Peat is harvested from lowland peatlands, and most is harvested overseas, with small amounts coming from the Fens, Somerset, the North West and Scotland. Until recently most peat came from Ireland, but the Irish government has now stopped all licences for peat extraction and now peat is imported from the Baltic States. However, wherever it is harvested, carbon dioxide is still released, making it a global issue.
Supporters of peat argue that peat bogs can easily be restored by blocking up drainage systems and sowing seeds of sphagnum moss. They further argue that we can harvest 5-7cm of a newly created peat per year by growing moss on permanently wet fields . Unfortunately the facts don't stack up.
Peat bog restoration has been shown to have some success, and will be crucial to reaching net zero as the bogs stop releasing carbon dioxide and instead start to absorb it. However once restored, no more peat can be harvested and the area must be carefully managed to allow the mosses and other species to re-establish. The government has announced £4 million of funding for peat bog restoration, but with only 13% of all peatlands in England being in a near-natural state, much more investment will be needed.
Sphagnum moss farming may give us a source of around 5-7cm of moss per year, but this is not the same as peat. Experiments are ongoing, but it is hoped that moss cropped from permanently wet fields can be used as a material in composts of the future.
Peat bogs are an invaluable habitat for flora and fauna, supporting many rare and vulnerable native species not found anywhere else. Peat extraction wipes out the entire eco-system and although habitat regeneration schemes are now being attempted, there is no guarantee these will be able to replicate an undisturbed bog in terms of diversity. Peat bogs also create natural flood defences, soaking up excess rainfall and releasing it slowly, and naturally filtering it.
There are many kinds of compost, all used for different purposes. In our trials we concentrate on bagged compost for sowing seeds, growing on plants and filling pots of bedding and veg. However gardeners also refer to compost as the material they make on their compost heaps. This is a hugely valuable material for gardeners and is best used a a mulch on the surface of your beds. It helps the soil to retain moisture, meaning less watering, and slowly improves the structure and nutrient content of your soil as it breaks down.
This kind of compost is often sold as 'soil improver' at the garden centre. Some still contain peat, but many are now sold as peat-free and even peat's supporters believe that peat shouldn't be used to mulch beds. If you don't have your own compost heap, make sure you buy a peat-free soil improver.
The most common kind of bagged compost is multi-purpose compost, which is meant to be for every garden job. Our results show that some are good all-rounders, but some are better for some tasks than others. While these used to contain large amounts of peat, many are now peat-free or contain a reduced amount of peat, usually less than 50%.
You can also buy specialist composts such as for sowing seeds or growing on young plants, as well as for growing orchids, cacti or ericaceous. Our tests have shown that some of these specialist products can be very good, especially for sowing seeds.
Peat-free composts are typically made up from materials such as wood fibre, composted bark, coir and, to a lesser extent, composted garden waste. However, you can also find composts containing sterilised soil, vermiculite, perlite, grit and manure. There is even one series of composts made from composted bracken and sheep’s wool. It’s likely new materials will be have to be used to fill the gap left by the peat ban.
Wood fibre can be the shavings taken from lumber yards as timber is sawn into planks. However, more often it is treated. Chipped wood is wetted, pressurised and heated to turn it into a light, fluffy material. The result is a little akin to putting a woolly jumper in a tumble dryer: the fibres expand and split apart, making them better at holding air and allowing water to drain freely.
It's increasingly used in both peat and peat-free composts and typically makes up around 50% of the total volume. Wood fibre can lock up nitrogen, leaving plants starved of this vital nutrient, but manufacturers usually balance the fertiliser to get over this problem.
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 graded for size, with large pieces used for mulch, while small pieces are composted until it has leached any tannins, is inert and is starting to break down.
Coir is a fibrous material made from coconut husks and is milled to make a peat-like material for horticultural use. It mostly comes from southern India and Sri Lanka, and small amounts are sourced in South America.
It’s often mixed into peat-free composts, making up about 5-20% of the total, but you can also buy it on its own as a compressed block or as loose fibres. The blocks expand into a fluffy compost when water is poured onto them. Read the label when when you buy these: some contain fertilisers, but others have none and you will need to feed your plants as soon as you pot them up.
Coir is 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 amount of water needed to rinse salts from the coir. This is a major problem as it's produced in areas where clean water is scarce. Poor working conditions for the labourers producing it and, in some instances, child labour are also issues to consider.
Some manufacturers are working to mitigate the water issue with collection and storage during the rainy season and child labour is outlawed in the countries it is produced. However, it's almost impossible to track down the source of all coir and to verify that safe practices are used in every stage of its collection and processing.
In the past, peat-free composts were largely made from green compost, but it’s becoming less common due to problems with its variability and nutrient balance.
It’s a widely available and cheap material as it’s made from the green waste collected by local authorities or from municipal waste sites. In other words, it is very similar to the contents of your compost bin, but with notable differences, including:
Some manufacturers have now decided not to use any composted green waste in their composts and are using wood fibre instead. Other producers have altered where they source the materials for their green compost and have refined their composting process to ensure a good-quality product.
Getting used to peat-free composts when you have used peat for many years can seem daunting, but with a little care you should get very good results. For the past three years Which? Gardening has only used peat-free compost for all our growing needs at our trials site and so we know it's entirely possible to grow a wide range of plants without peat.
You may find you need to water peat-free composts more than peat, which naturally holds plenty of water. Peat-free composts are often very free draining, and so little and often in the key. This means you can keep your plants well watered without wasting water or washing out nutrients by over-watering.
It's not always possible to see how much water is in a pot from a quick glance. Some dry out on top but stay wet further down. Others develop a darker surface that can look wet when actually the pot is very dry. Get used to picking up small pots to weigh them - a heavy pot won't need water, but a light one will. With larger pots, push your finger down the side of the pot to feel the compost below the surface daily.
Most composts contain a small amount of fertilisers and in peat composts this runs out after four to six weeks. In some peat-free composts, it can run out after only around three weeks. Keep a close eye on your plants and add a if the growth or flowering of your plants slows down. Even young plants benefit from a liquid feed and you may need to give them a dose weekly until you pot them on or plant them out.
Some coir composts contain no feed at all. If you prefer to use these, add a weak dose of liquid feed as soon as your seedlings emerge and until they are ready to pot on.
Plants that will stay in containers for a long time, such a pots of summer bedding or shrubs and trees in pots, benefit from a . These will feed your plants for months, and pots filled in May will usually last into September before the fertiliser starts to run out. After this, supplement with a liquid feed to keep your plants looking good until the first frosts.
Our tests have shown that peat-free compost deteriorates in quality if kept for too long. Aim to only buy as much as you need and if you have any left over, keep it in a cool, dry place such as in a shed or garage. Peat-free compost left out in the rain or in the sun won't be fit to use after around three months. If yours has been sitting around for a while, use it to mulch your flower and veg beds.
Peat-free compost used to be very hard to get hold of, with very little choice in most garden centres. The situation is now better than it was, but we're hoping to see great improvements over the next few years as the ban on peat use comes closer.
As a result, Which? Gardening has changed how we choose composts for our trials and now prioritise peat-free products. Where we do include peat, we select only widely-available composts that have a low peat content. From 2022 we will no longer include any compost with more than 60% peat in our trials.
It's impossible to know how good a compost is just by looking at the bag. Even well-known manufacturers don't always make good products and as they frequently change the formulation, you can't even rely on this year's compost being as good as the one you bought last year. But there are a few ways to be sure you're buying a good bag.
Check our compost results and find out which garden centres stock our Best Buy composts. If possible, ring ahead to make sure the bags are in stock and have arrived recently. When you're at the garden centre, make sure you check our online pages to make sure the design of the bag is the same as on our reviews. That way you'll know it is this year's compost and should be fresh.
Make sure the bags look new and aren't faded or torn. If they are, they might have been sitting in the sun for too long, which will make the compost deteriorate. If the bag is very heavy, it has been rained on repeatedly, which also causes the compost to degrade. Try to buy from a garden centre where compost is kept under cover.