If you’ve been in the houseplant hobby for a while, you’ll have encountered peat. This material is a very common soil additive and has a bunch of properties that make it handy for use with (house)plants. There is, however, one little problem: it’s not a sustainable resource.
In this guest post from Swiss online plant store Feey, we go into the uses of peat and why you might want to skip it in favor of other soil amendments.
What is peat?
Peat is found in most of the pre-mixed soils you can buy in shops. These soils contain up to 90% peat. But here’s what you should know: With peat you are holding a valuable piece of marsh in your hands. Yep, peat is nothing more than drained marsh soil!
A short biological and geographical digression for those interested: peatlands are a wetland type. They are always slightly submerged in water. That’s why hardly any oxygen reaches the soil. Dead plant parts are not completely decomposed, and instead of humus, peat is formed.
This takes an incredibly long time. In a year, a layer of peat grows about 1 to a maximum of 10 millimetres. The Devil’s Moor near Worpswede in Germany, for example, grew for 8,000 years before it looked like it does today. Huge peatlands still exist nowadays, especially in Russia, Alaska and Canada.
As you may already have guessed, by cutting peat away for commercial use, one removes much more than just 1 millimetre a year. This used to be an incredibly common practice in England and Ireland for example, where peat was used as a fuel source.
Even now that peat has become redundant as fuel, it’s still being harvested for human use. Specifically, by the horticultural industry.
Why peat doesn’t belong in the soil of houseplants, but in our peatlands
Peat cutting uses drainage channels to drain peatlands that have existed for thousands of years. In most cases they don’t recover from this.
This means that countless animals and plants lose their habitat. These include the sundew, the moor frog, the moor lizard and many butterflies, dragonflies and other insects that specialise in moors. In Germany, 95% of their habitat has already been completely destroyed!
Peatlands are also essential for humans. They can absorb massive amounts of water (they’re constantly wet) and if they dry out, the danger of flooding increases. Normal soil simply cannot hold these water masses.
Don’t be dazzled when ‘they’ say the moors will be restored to their natural state. That is what the authorities in some countries are demanding. But let’s hear the facts: it takes 1,000 years to rebuild just one meter of peat. How long will it take for the animals and plants to reestablish themselves? Who knows.
Did you know? In some countries, such as Canada, government and horticultural companies claim sustainable use of their peatlands, leaving them to regrow after harvesting an area for a certain amount of time. Whether this is actually effective and restores the marshes to their original state can be debated. Some sources suggest the practice still contributes to CO2 being released
The Myth of Permanent Peatlands: “Peat moss is an environmentally friendly organic amendment essential for many
horticultural purposes”
Peat extraction is bad for the climate
Last but not least, our troublesome old friend climate change is making an appearance. Peat soils act like a sponge for harmful greenhouse gases. They store twice as much CO2 as all the world’s forests combined.
If oxygen gets to the peat when it’s being drained, a whole lot of carbon dioxide is released into the atmosphere. Nitrous oxide is also released – which is even 300 times more harmful to the climate than CO2.
You don’t think the effects are that serious? Then listen to this: In Germany, destroyed peat soils release about 40 million tonnes of greenhouse gases every year. That’s the same amount as the entire German aviation industry.
3% of the earth is made up of peatlands but they store 33% of the CO2.
What is peat used for? The advantages and disadvantages of peat for our plants
Peat certainly has its function in common potting and plant soil.
Peat does this well:
- Stores water – much, much more water than its own weight
- Loosens the soil
- Makes the soil more permeable – water and nutrients reach the root tips of your plant
However, peat also lowers the pH-value in the soil, which can be an advantage or disadvantage depending on the plant. Peat is far too acidic for many plants – except for marsh plants (ha! Who would have thought!). Rhododendrons and hydrangeas also like acidic soil.
Houseplants, which often come from tropical regions, are less happy about this.
Peat is low in nutrients. Many gardeners don’t mind this since they can adjust the nutrient content of their soil themselves and according to the needs of the plant. And peat can be mixed well with clay, sand, lime and fertiliser.
But peat also has clear disadvantages for plant care:
- Yes, peat stores water very well. But once the soil has dried out, peat absorbs moisture very poorly. This is called poor “rewettability”. You may water your plant and it still dries out.
- Peat, as we have seen, hardly allows room for oxygen. This increases the risk of waterlogging in the plant pot over time. The roots will sit in water and rot.
- Black peat has poor structural stability. This means it collapses over time and loses its volume.
The bottom line: no one needs peat. The advantages for our houseplants are minimal. And certainly not outweighed by the destruction of thousands of square kilometres of rare peatlands.
By not using peat, you are not only doing something good for the earth, the moorlands and your conscience, but you can nurture your plants just as well.
Peat-free soil: Which are the alternatives and how good are they?
The Zurich University of Applied Sciences (ZHAW) has published research on which peat alternatives are good and how good they are exactly. Can they store water? How airy are they? And above all: What does the life cycle assessment say?
Let’s open the door: all, ALL alternatives have a better life cycle assessment than peat. Depending on the combination, greenhouse gases can be reduced by 62 to 97 percent.
Of course, it would be best to use indigenous, renewable raw materials or waste products that are being produced anyway. However, none of these alternatives can replace peat entirely. The motto is to mix wisely. We give our tips on how to do this below.
Here are our favourites for now.
These are the best peat alternatives:
a) Coconut fibres or coconut soil
Coconut fibre is made
- from the dried bark of coconut palms,
- from pieces of coconut shells that are soaked in water for a few weeks and then shredded,
- as waste from the manufacture of mats, ropes and carpets, or even coconut oil.
The pressed blocks, tablets or bricks can be soaked in water at home and you have wonderful indoor plant soil. The long-lasting, super-light fibres swell to about eight times their volume. It will say how much water you need on the packaging.
Coconut fibres, also known as coco coir, have a lot of important advantages. They…
- loosen the soil
- decompose slowly and provide a stable structure
- allow enough air to reach the roots (i.e. less risk of waterlogging and root rot)
- are permeable – if you water too much, the rest of the water simply runs off
- have a less acidic pH-value than peat
- retain moisture (and nutrients) well and release both evenly to the plantlet
- can be rewetted easily
- are sterile – pests, fungi and mould spores do not stand a chance.
Plants like coco very much.
Coconut fibres are rather low in nutrients, so they need to be fertilised more than peat soil. The easiest way to do this is with slow-release fertiliser. Because coconut fibre is sterile and low in nutrients, it makes a great growing medium for your cuttings (baby plants).
Coconut fibre dries out more quickly at the top than further down. Therefore, be careful not to water too much, but first reach deep into the pot with your finger to check how wet the soil is.
You don’t have to worry about the environment either: It’s possible to find sustainably grown coconut palms, and coco soil is made from the waste products that are being produced anyway.
b) Wood fibres
Waste wood is defibrated under high heat and pests are killed. The result is wood fibres: As a substitute for peat, they ensure a fine-crumbled and loose structure of the planting soil and good aeration. And when it comes to environmental impact, they are ahead of the game. No other peat substitute can keep up – and peat doesn’t even come close.
But: wood fibres hardly contain any nutrients, so they need to be fertilised more often (especially with nitrogen). Plus, they store water very poorly. So you do have to water more often.
If you are a water lover anyway, wood fibres might not be bad at all. They can be rewetted well and excess water can drain away easily – waterlogging doesn’t stand a chance. That’s handy, since overwatering is a prime cause of death for houseplants!
Note that wood fibres somewhat collapse over time, so you can top them up a bit on a regular basis.
Photo courtesy of Feey.
c) Compost
You’d better take your compost outside – thanks, says your nose. But there are composts that don’t smell funny and have many advantages.
Compost contains many of the important nutrients for your plants, especially phosphate and potassium. According to some sources, the nutrient density in compost even wards off pathogens and pests. Its structure is good, but because compost continues to decompose over time it will collapse a little. Then you may have to add some soil and repot again.
Compost also has good rewetting properties. It can dry out completely and then soak up water again well and evenly without becoming waterlogged.
However, compost has a bad reputation: depending on its production and composition, it is said to be contaminated with heavy metals or other undesirable substances. Make sure to buy certified quality compost. In professional composting plants it is tested for pollutants and the experts also check whether it contains all the neccessary nutrients for your plants.
d) Bark humus (bark compost)
Humus is made from small pieces of coniferous bark (mostly from spruces) that are composted at high temperatures. This way, microorganisms and pests die off. The bark we can use is produced as a by-product in sawmills. This raw material is therefore relatively sustainable.
Bark compost absorbs water and nutrients well and releases them slowly to the plant – and evenly, even if you water and fertilise irregularly. The humus has a good structure and a stable pH-value. But it also dries out more quickly on the surface than at the roots.
In principle, however, bark humus is among the best peat alternatives out there. Many peat-free soils therefore consist of about 50% humus.
e) Land soil
Land soil is produced during sugar production. The name is not very fanciful: it really is just soil from the land. The sugar beet brings soil residues to the sugar factory, which are then washed. The soil is dried under high temperatures.
Land soil cannot compete with the properties of peat, but it is suitable as an additive for peat-free soils. Land soil “enlivens” the substrate with useful microorganisms and, thanks to the clay it contains, ensures stability and good rewettability.
f) Peat moss
Peat moss is a great alternative on paper because it has almost the same properties as peat.
Peat moss is grown on high moorland areas that have already fallen victim to peat cutting. You re-wet these areas and plant peat moss (better known as sphagnum), which grows quickly. Very similar to peat, just less old. In the first trials of 2016, plants throve wonderfully in soils that contained about 80% peat moss – a one-to-one substitute for peat!
So (almost) all is well: it is a relatively fast-growing raw material, the peatlands are preserved and less CO2 is released. Not perfect, but heaps better than draining more peat bogs.
But beware: peat moss is still quite expensive because it would have to be cultivated in huge quantities. Canadian peat moss seems easiest to find, as the country has dedicated itself to cultivate it on a large scale.
We wouldn’t really recommend these peat alternatives:
g) Xylitol
Let’s keep it short – xylitol and peat share many advantages, but also the disadvantages. Xylitol is a precursor to lignite and is a by-product of coal mining.
It is loose, acidic and structurally stable, and like peat, mixes well with lime and fertiliser to generate the perfect mix for each plant.
However, xylitol stores very little water. Like peat, xylitol is a fossil organic substance and harmful to the climate.
h) Does organic soil contain peat?
Unfortunately, you can’t bet on it. Sometimes even organic soil contains up to 90% (!) peat.
Beware of marketing fraud: “peat-reduced” or “peat-farmed” can be called anything that contains up to 80% peat. (Of course, 80% is still less than 90%…).
Only “peat-free” is peat-free.
Soil without peat is just as good as soil with peat. You don’t find it everywhere yet, but you can’t reproach it for its quality.
Peat-free soil: How you can replace peat.
It’s the combination that counts.
Coconut fibres are a great alternative to peat. Try to combine the coconut fibres with gravel, sand and clay so that the soil has a stable structure and allows enough air to reach the roots.
Additionally, you can mix the soil with vulkastrat, which is a mixture of pumice, lava rock and zeolite. It absorbs water particularly well and releases it evenly to the plant, but it might be hard to find. You can also use other aerating gritty materials like perlite, pumice or volcanic clay.
The more permeable the soil needs to be for a particular plant, the more gritty material should be used. Repotting cacti, for example, can be done with only grit!
Mixing your own peat-free soil: this is how it works.
What you need:
- 2 parts quality compost or quality soil without peat
- 2 parts bark humus, wood fibres or coconut fibres
- 1 part quartz sand or washed sand
- 1 part perlite, volcanic clay or pumice
Depending on your plant, the soil has to be rather permeable or store more water. You can play around with the quartz sand and volcanic clay/pumice/perlite accordingly.
Mix everything well – and your peat-free soil is ready.
If you have any more questions about peat, its uses and its sustainability or want to share your own opinions, don’t hesitate to leave a comment below. Happy planting! 🌿
Sphagnum moss photo © Goran on Adobe Stock.
Other sources:
- https://www.bafu.admin.ch/bafu/de/home/themen/wirtschaft-konsum/fachinformationen/torfausstieg.html#-657567436
- https://www.bafu.admin.ch/dam/bafu/de/dokumente/wirtschaft-konsum/fachinfo-daten/torf_und_torfersatzprodukteimvergleich.pdf.download.pdf/torf_und_torfersatzprodukteimvergleich.pdf
- https://www.bafu.admin.ch/dam/bafu/de/dokumente/wirtschaft-konsum/externe-studien-berichte/erweiterung-studie-torf-und-torfersatzprodukte-im-vergleich.pdf.download.pdf/Stucki_et_al_2019_Erweiterung_Torfersatzprodukte_im_Vergleich_v3_0.pdf
