Peat-free compost: expert guide

What is peat-free compost?

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. To put this in context, the average person emits 10 tonnes per year in the UK. 

It's clear that we won't reach net zero while peatland is still drained and the peat extracted. A ban on the sale of peat has been suggested, but there are no plans to introduce one at the moment. That said, most manufacturers have stopped producing peat compost, or are well on the way to being peat-free. 

The good news is there is now a concerted effect to improve peat-free composts and they are more readily available. Our trials show that many peat-free composts are now as good, or better, than peat-based products. You may find it looks and feels strange to use, but there are some simple rules to keep in mind for successful growing. 

Take a look at our compost test results to see how they compare. 

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How to get the best from peat-free compost

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 six years Which? Gardening has only used peat-free compost for all our growing needs at our trials site, so we know it's entirely possible to grow a wide range of plants without peat.  

Watering

Peat-free composts are often very free draining, and so little and often is the key to good watering without either 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 composts 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. 

After sowing seeds or potting up young plants, we find it easiest to water seed trays and small pots of compost from below by soaking them in a water bath, around 3cm deep . The water will be pulled up through the compost. Allow them to drain well and then water from the top using a fine rose when they next need it. 

The water-bath method is also a good way to re-wet pots and trays that have dried out completely. To avoid drying out, water little and often to make sure your plants stay at the optimum moisture level. 

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Feeding

Most composts contain a small amount of fertiliser, known as a base fertiliser, but this generally runs out after around three to four weeks. Keep a close eye on your plants and add a liquid feed as soon as the growth or flowering of your plants slows down. 

Even very young plants benefit from a liquid feed. Our trials have shown that seedlings benefit from a low dose of liquid feed applied every week from the time the first true leaves unfurl. Some liquid feeds, including one of our Best Buy feeds, state a dosage rate for young plants. Choose a balanced feed or one that is very high in nitrogen. Avoid a feed that is high in potassium, such as tomato feed. 

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. Alternatively mix a controlled-release feed into the compost. 

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 controlled-release fertiliser. 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. 

Try the best tomato feeds from our expert tests

Storing your compost

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 always look for fresh bags that have been delivered recently. It's best to buy from garden centres that store it under a roof where it won't get sodden in the rain. 

If you don't know how much you'll need, we found that coir blocks store well and don't degrade over time. 

If you have any compost 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 can still be used for most purposes, but you'll have better results with fresh compost. 

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Is bagged compost the same as garden compost?

There are many kinds of compost, all used for different purposes. In our trials we concentrate on bagged compost for sowing seeds, growing plants on 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 as 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. 

Buy one of the best compost bins and start to make your own. It's not as complicated as you might think. Just follow our simple advice on how to make compost.

Soil improvers

Many gardeners have used bagged compost as a mulch on the garden or dug it into the soil. However, this isn't a good idea, as peat composts do little to improve the soil as they oxidise and break down too quickly, releasing carbon dioxide. They don't add enough organic matter to feed the soil or to help create a better soil structure. Peat-free composts can be used, but there is a shortage of the right raw materials to make these, so our advice is to use home-made compost or buy a bag of soil improver. 

Soil improvers are mostly made from green compost or biodigestate – see our description of these belpw. You can also used well-composted manure as a soil improver. 

Which? Gardening carried out a test to find the best soil improvers and found that any bagged soil improver or home-made compost created a better soil structure and added valuable plant nutrients. You can even empty the peat-free compost from your containers onto your beds at the end of the season to improve the soil structure.  

Our three recommended soil improvers are:

Camelot Horse Manure

We tried this brand as it was available in the local garden centre, but we recently found little difference between branded bags of manure (see box). The bags were heavy to carry and when it was spread it contained some lumps, but there was no bad smell. It incorporated well into the soil leaving a crumbly texture after digging and the potato crop was excellent. 

Price £5.99 for a 40L bag 

Where to buy Garden centres

Melcourt SylvaGrow Farmyard

This is made from a blend of anaerobic digestate, a by-product of green-energy production, and carefully monitored green compost. While it didn’t incorporate well into the soil when applied as a mulch, it had a good texture, was easy to spread and dig in, and kept the weeds down. It produced a good crop of potatoes. 

Where to buy 

Miracle-Gro Peat-free Premium Border Booster

This is manure and green compost with added organic fertiliser. Interestingly, it’s recommended it's spread on the surface of the soil, and not forked in. That said, it incorporated into the soil down to 5cm, better than most other products, and produced a huge harvest of large potatoes thanks to the added fertiliser. 

Where to buy 

Mulch

What is mulch?

Mulch is applied to the surface of the flower border or veg bed. There are two main kinds: biodegradable ie one of the soil improvers, and non-biodegradable, such as gravel, pebbles or landscape materials. We'll concentrate first on biodegradable mulches. 

Any bagged soil improvers will work well and your own garden compost is very good as it improves the soil quality. You can chip your own woody pruning and use these, but compost them first to stop them taking nitrogen from the soil. Which? Gardening research found grass clippings weren't hugely effective. 

There are also some very good commercial products on the market, including Strulch, which is made from treated straw. We use this at our Capel Manor trials site to keep down weeds, maintain a good level of moisture in the soil and deter slugs and snails. 

You'll see bags of bark chippings at garden centres, which won't add nutrients to the soil, but are an effective way to prevent weed growth. 

What does mulch do? 

The idea is simple but it carries out several important tasks. 

• Mulching the ground prevents moisture from evaporating quickly, helping to hold onto water that has been applied through irrigation or rainfall. This saves you time when watering in the summer, and means you're less likely to have to use mains water on your garden. For more on water-efficient irrigation, see you automatic watering systems reviews. 
• Any organic material left on the soil surface will rot down and be eaten by worms and other soil-dwelling invertebrates, slowly getting incorporated into your soil as humus. A good soil needs plenty of humus as it helps to retain water, but also releases nutrients to feed your plants and makes it easier to hold onto these nutrients so they can be easily taken up by plant roots. Worms, which are attracted to soils with plenty of organic matter to eat, also help to improve the structure of the soil, allowing water, air and nutrients to circulate and making it easier for roots to grow. It helps to break up a sticky clay soil into smaller particles, and gives body to a sandy soil. 
• Mulch increases the soil temperature, keeping your soil warmer through the winter. When Which? Gardening tested mulches, we found that Stulch kept the soil 1.6^oC warmer overnight than bare soil. As a result you can start to plant into mulched borders earlier than you can with bare soil. Mulched soil is cooler through the summer as it retains more water, so it offers better protections to your plants on very hot days. 
• Mulching improves the appearance of bare soil and keeps your plants free of mud splashes after heavy rain. This is particularly noticeable through winter when you see more soil and low-growing, spring-flowering plants such as snowdrops, crocuses and hellebores are at their best. 
• Bare soil can form a 'cap' when the surface hardens due to a combination of rain compacting the soil surface and the sun baking it. A mulch prevents that cap from forming, which means that rain drains more easily into the border, but air can also percolate. Roots need air to function properly. 
• Finally, but crucially, mulching covers the soil surface, so deterring weed seeds from germinating. Weeds not only look unsightly, but also take up valuable resources such as water, nutrients and light that should be enjoyed by your prize plants.  

Discover the best ways to control weeds in paving and paths

How do I apply mulch? 

Spring and autumn are the best times to apply mulch. Weed the area before you spread it and make sure the soil is damp. 

Apply a layer around 5cm deep. Don't mulch right up to the crown of plants, but leave a gap of around 5-10cm around plants to avoid stems from rotting. If you're mulching in autumn, reduce the depth of mulch to just 2cm over places where you have spring bulbs or your could retard their growth. 

You may find you need to apply mulch twice a year, as it may break down and get pulled into the soil quite quickly, especially on free-draining soils such as chalky and sandy ones. 

Make things easier with the best wheelbarrow

How else can I cover the soil? 

You can cover ground with gravel or larger stones. These have many of the benefits of biodegradable mulches, including reducing weed germination and retaining water, but obviously they won't rot down to improve the soil. 

Alternatively you could use a weed-suppressing membrane, which will stop the weeds from growing and are a quick way to clear ground ready for planting. They can also help to raise the soil temperature, meaning you can plant a little earlier than if you left your soil bare. They will also prevent the soil from capping in heavy rain. 

Read our reviews of the best weed suppressing membranes. 

How to buy the best peat-free compost

The choice and availability of peat-free composts has greatly improved over the last few years. Garden centres stock far more than before, but there are also some excellent products sold online. 

As a result, Which? Gardening has changed how we choose composts for our trials and we now only trial peat-free products, except for one, Moorland Gold, which is made from peat particles filtered from lakes and dams during the purification process for drinking water.

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, 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.  

Check that 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. 

Our comprehensive compost trial results will tell you everything you need to know, so you can choose the best one for your garden. 

What about plants bought in garden centres? 

A good number of UK nurseries have now made the switch to using peat-free compost, but others are still using peat in part or all of their production process. Many growers have information on whether they are peat-free on their websites. 

In the meantime, you're likely to find a mix of composts used in the plants you buy at the garden centre or online. Many plants come from the Netherlands, where the transition to peat-free is further behind than in the UK. If you want to avoid plants grown in peat, speak to the staff at your garden centre, or seek out UK peat-free nurseries. The Royal Horticultural Society has a handy list. 

What are the problems with peat?

Peatland covers just 3% of the planet, but through its unique qualities it's able to store twice as much carbon as all the forests in the world. It also has the possibility to store far more of the carbon we will emit in the coming decades, making it an invaluable resource. Currently just 13% of the peatlands in the UK are in a near natural state, and their carbon holding and sequestering capacity is compromised. 

Peat is an accumulation of partially decayed vegetation, created primarily 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. 

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 ecosystem, 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. 

To harvest it for use in compost, peat bogs are drained and cleared of all vegetation. Harvesting not only removes around a 20cm layer of peat every year – in other words, a century’s worth of peat accumulation – but also allows the exposed peat to oxidise, releasing carbon dioxide.

Peat is harvested from lowland peatlands, and most is harvested overseas, with small amounts coming from the Fens, Somerset 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 it 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 £11m of funding for peat bog restoration, with plans to restore 35,000 hectares of peatland by 2025, but far more is needed.

Sphagnum moss farming may give us a source of around 5-7cm of moss per year and may provide at least some material to add to peat-free composts. Experiments are ongoing, but it's hoped that moss can be cropped either from permanently wet fields, or from greenhouses where the conditions are more stable and sterile.  

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What's in peat-free compost?

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's one series of composts made from composted bracken and sheep’s wool and worm casts are also used in other composts. It’s likely new materials will have to be used to fill the gap left by the peat ban.  

If you're concerned about the green credentials of your peat-free compost, there is now way of checking. The Responsible Sourcing Scheme rates composts against seven measures: energy use; water use; social compliance; habitat and biodiversity protection; pollution; resource use efficiency and renewability. Many compost manufacturers are now part of the scheme. You'll see a QR code on the bag which will take you to the Responsible Sourcing Scheme website where you can see how well your compost scores. 

In our trials we've found some excellent peat-free composts. If you haven’t yet switched to peat-free, try our best peat-free composts. 

Wood fibre 

Wood fibre can be the shavings taken from lumber yards as timber is sawn into planks. However, more often chipped wood is wetted, pressurised and heated to turn it into a light, fluffy material. The result is somewhat like 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 

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 

Coir is a fibrous material made from coconut husks. It mostly comes from southern India and Sri Lanka, and small amounts are sourced in South America. The fibres used in compost are the small particles that fall away are the larger fibres are stripped off the coconut to make mats. 

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. Consciensious manufacturers have put in water-storage facilities to collect rain water. Transport is also a concern, given how far away it is made, but it is transported as dehydrated blocks, which reduces its volume and weight. Labour issues are also key, as it's manufactured in areas of the world where working conditions and legislation are very different to those in the UK. 

Green compost 

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's very similar to the contents of your compost bin, but with notable differences, including:

• The amount of woody prunings. While these are chipped and graded before being composted, it’s not unusual to find large chunks in your compost. These make it hard to use for sowing seeds and potting on seedlings and plug plants. 
• It usually contains large amounts of grass clippings that may carry lawn-weedkiller residues. These don’t break down when composted and may harm your plants. 
• It’s not unusual to find bits of plastic, glass, stone and metal in the compost, despite attempts to filter them out in the composting process. Microplastics are often found in green compost. 
• Nutrient imbalances can also be a problem. Due to its make-up, green compost contains high levels of chlorides, which can prevent plants from taking up the nitrogen needed for leafy green growth.
• It often contains large amounts of potassium, which can cause calcium and magnesium deficiencies in the plant.

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.

Learn how to make your own garden compost

Biodigestate

We're starting to see a few composts made from biodigestate. This is a by-product of anaerobic digestion for electricity generation using the stalks from cereal crops and animal slurry. These are put into vats and fermented, giving off a gas which is burnt to create electricity. Once the process has finished, the remaining material is then bagged up for use as a soil improver, mulch or compost.