How to choose a good peat free potting mix (or compost)
If you've grown in a peat free potting mix (or 'compost' as we call it in the UK), you may have found a significant variability in quality. In my experience, some perform superbly, many are fairly average, but poor quality is not uncommon either. In the UK, the sale of bagged peat products to amateur gardeners is to be banned from 2024. Peat is being phased out because its harvest releases large volumes of greenhouse gas, and damages precious wetland habitats. So it's important we all become more savvy about the different peat free options. Particularly, as the quality of a potting mix does makes a big difference to how well plants grow. The fact that different potting mixes all look similar when in bags, makes it useful to know what we are looking for inside the bag. This is quite a long post. If you don't have the time (or the will!) to read it all, here is the essential info:
- Peat free potting mixes are not all equal - and are made from a variety of different materials.
- No one material is best, but coir and composted bark or woodchip based mixes tend to be more consistent and generally last well over several years. They are often more expensive but can be a good investment long term.
- Green waste composts tend to be lumpier and more inconsistent. However, they can be good and are often low cost and made locally from sustainable materials.
- The quality of the potting mix has a big impact on how well plants grow. So it's worth doing a bit of research to find a good one that is easily available to you in your area.
What are peat free mixes made of?
Peat free mixes are not all the same. Most are made from one or other of three ingredients: coir (coconut fibre), composted bark / wood chip, or green waste. Or sometimes a blend of all three. There are also a few potting mixes that use completely different ingredients. Dalefoot compost, for example, is made from sheep's wool and bracken. But these are unusual - the vast majority are based on coir, wood chip or green waste.
What's the difference between these ingredients?
The common ingredients that peat free mixes are made of each have different pros and cons:
Coir or coconut fibre is a by-product of the coconut industry, usually shipped from India or Sri Lanka. It can make an excellent peat free compost. It drains well, holds water well, and rewets easily. It’s also available in neat, compressed ‘bricks’, that swell when reconstituted with water. This makes it ideal for those of us who need to carry our dirt up several flights of stairs. It has a pleasant smell and is nice to work with. In its raw form it is low in nutrients, and requires an added fertiliser to work as an effective potting mix. Most bagged coir mixes come with fertiliser pre-added. Some coir bricks come with added fertiliser, some require you to add fertiliser yourself. Check before you use. Coir is one of the more reliable and consistent (as long as it has fertiliser added) peat free ingredients. However, just occasionally can contain high levels of salt which are bad for plants. (I bought a batch about ten years ago that seed germinated very poorly in).
Composted bark and wood chip
Composted bark is a by-product of the timber industry. Wood chip comes from a variety of sources, including hedge trimming, tree surgeons, and saw mills. They both hold air and drain well. They are also long lasting, retaining texture and structure well over several years. And they normally have a pleasant woody smell. Composted bark / wood chip tends to be more consistent than green waste (see below). But, of course, there are lots of variables including what type of wood is used and how well it has been composted. Generally, though, it makes a good to excellent potting mix.
This is Sylvagrow compost which is a blend but mainly composted bark and woodchip. It's also nice to work with and lasts a long time.
Green waste compost
Green waste compost (or 'green compost' as it is now being branded) is made from park and domestic grass clippings, hedge prunings, and sometimes food waste. I wrote a blog post about it a way back, here. Because it is made all year round with whatever waste is available, the ingredients vary significantly from season to season. No grass clippings in winter, for example. For this reason, it tends to be more inconsistent than other peat free ingredients. It can sometimes have quite a pungent, unpleasant smell. Luckily, this doesn't necessarily affect how it performs. I once had a bag that was all clogged together and smelt terrible but the tomatoes grew great in it. Some green composts contain large lumps of wood. This can help improve drainage but may require sieving to make it suitable for sowing seeds in. Occasionally it can also contain bits of plastic and other contaminants. I once found a toy plastic gun in a bag of municipal compost! However, processes to remove unwanted materials are gradually improving. Despite its variability, green compost can still be made into a good potting mix, as long as their is good quality control. However, even when buying the same brand, it is prone to to vary quite a lot from batch to batch. So it can be more hit and miss - but is getting better. Green compost is often available at low cost from local councils / municipalities. Look for those that have the PAS 100 quality standard (this ensures it is tested for heavy metals and weed seeds). In my experience, municipal compost tends to be particularly variable. Sometimes it is good! I once helped out in a container garden run completely on municipal compost. And they grew good veg in it. It's an option worth experimenting with, particularly for more experienced gardeners.
This is an example of green waste compost (rather wet as it had just rained), made by at my local council recycling facility. It has fairly large bits of twiggy wood in it - which is not untypical for the cheaper mixes based on green waste. It's not too bad for growing larger plants in - but benefits from sieving before seed sowing (and even then isn't that reliable for seeds). The higher quality brands that use green waste are normally less lumpy.
Which peat free potting mix to choose?
There isn't really one best choice for all situations. But here are some of things that it is useful to consider when choosing:-
Premium or budget brands?
The main differences between the more expensive and budget brands are quality and consistency. Premium brands invest more in procuring good ingredients and rigorously testing each batch. While this can never guarantee that every bag will perform superbly, it does significantly reduce the risk of a poor one. Cheaper brands - for example budget supermarket own brands - on the other hand, are prone to more variability, particularly those based on green waste compost (which most are). They can be good, but mediocre and poor quality bags are also not uncommon. They are worth a go. But try to resist the temptation of buying lots of bags until you've tested one. I'd also try to stay clear of the budget brands if you are beginner. It's harder to spot poor quality compost - or to know how to manage it - until you have some experience. That said, if budget is the only option, don't be deterred from giving it a go. Just bear in mind that if things don't grow well, it may be down to the compost and nothing to do with you. In general, though, a good quality potting mix is a good investment - and one of the best things to spend your gardening budget on.
Which can be re-used for longest?
Another consideration is how many years a potting mix will perform well for. I’ve been growing tomatoes in the same coir and composted bark composts for four years now. The composted bark has retained its structure better than the coir, but the tomatoes have grown well every year in both. I haven’t tested it to the same degree, but my observations suggests that green waste compost is more prone to losing its structure after a year or two. The good news, however, is that nearly all peat free composts perform much better than peat when comes to re-use. For longevity - and based on my observations so far - I'd recommend composted wood chip mixes first, followed by coir.
These tomatoes are growing in four year old compost wood chip (left) and four year old coir (right). The plant health and crop is still excellent.
Which is most sustainable?
As a bulky, heavy material, transport is the main environmental impact. The most sustainable option is to make your own compost. But most of us don't have the space for this, s0 what’s the next best option? Look for products sourced and made in your region or country. Locally made, green waste compost is often a sustainable choice - but you need to weigh that up with its inconsistency. Coir is often touted as a sustainable material - and it is a waste product. But it is also shipped long distance from India and Sri Lanka. Composted wood chip - as long as it isn't shipped long distance - is often a better choice. Alternatively, a good compromise is to reduce the amount of potting mix you need to buy each year. Choose a long lasting material - like composted bark or coir - and learn to reuse it each year. You could also learn to make your own worm compost to recycle your food waste - and help add fertility back into your compost each year.
Which is the lightest weight?
If weight is an issue, coir is a good choice, followed by composted bark. Avoid any mix with ‘added topsoil’ or loam as this adds significant weight. Perlite is often added to light weight mixes. It works well, but this needs to weighed against the fact that it is very energy intensive to make.
Which is the most pleasant to use?
Coir is perhaps the cleanest and most pleasant smelling material to work with. A good choice if you have to do your seed sowing on the kitchen table or near your favourite carpet! Composted wood chip is also nice to work with. Green waste compost can be more smelly and 'dirtier'. This isn't necessarily a problem, but it's worth bearing in mind before you lug it up the stairs.
Which brands are best?
The availability of different brands is very location specific, varying from country to country, even city to city. To find a good one you often need to ask experienced gardeners in your area, look for online reviews, or seek advice in a good independent garden centre. Two brands I've used and like - and that are quite widely available in the UK - are Sylvagrow and Fertile Fibre. Of course, there are other good ones, too. Homebase and B&Q mixes often get good reviews, and Dalefoot have a strong following. Also, check out the experience of other gardeners - around the world - in the helpful comments and posts on the Vertical Veg Facebook Page, Facebook Community and on Instagram. Elsewhere on the internet, Pumpkin Beth, did an interesting trial of different peat free compost here. If in doubt, try a bag or two - and compare a few different ones. You can learn a lot in the process - and hopefully find one you particularly like.