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Peat and Peat Moss Alternatives

The horticulture industry is being blamed for depleting peat reserves and environmentalists are calling for a stop on using peat for growing plants. What are the peat moss alternatives? Is there a suitable substitute?

The horticulture industry would have no problems switching to another product instead of peat. After all, most gardeners are quite aware of the importance of preserving our environment. In this post, I will look at several peat moss alternatives to see if there is a viable option.

Peat and peat moss alternatives

Closeup of growing peat moss

Status of Global Peatlands

In my last post, The True Story of Peat, I reviewed the facts about peatlands and the use of peat. It is quite clear that peatlands are not in danger of being depleted. Quite the opposite, 86% of the global peatlands are untouched by humans. We have vast peat reserves and nature is making peat far faster than we are using it for horticulture.

The majority of peatland loss is due to agriculture and forestry. Horticulture uses a fraction of one percent of the total peat harvested each year. Horticulture is not the problem but we should always look at ways to reduce our environmental footprint.

Peat – the Perfect Product for Growing Plants

Peat and especially peat moss is the perfect medium for growing plants in pots. It has a high pore volume, holds moisture and air well, has a stable structure and the low pH is easily adjusted. It is relatively inexpensive and free of contaminates such as seeds, pests and diseases.

It contains active microbes that slow down the spread of disease better than other heat treated substrates (ref 1).

Peat moss is a natural organic product that is both acceptable to organic gardeners and adds no contamination once added to the garden.

An alternative product needs to meet most, if not all, of these conditions and it must have a lower impact on the environment.

Responsible Use of Peat

It is common to throw out statements such as “there are many alternatives to peat” but these statements mean very little unless the specific application is also specified. Before I look at peat alternatives, it is important to look at how peat is used in horticulture. Different applications can make use of different alternatives.

Peat as a Mulch

Peat can be used as a mulch in gardens but it dries easily and is then blown away by wind. Several other products like aged manure, compost, and wood chips provide a much better alternative to peat for this application.

Growing Seedlings

Peat moss is ideal for germinating seeds and growing seedlings. Its porosity makes it easy for young roots to penetrate and the anti-fungal properties help control infction. The relative amount of peat used for this application is very small and finding an alternative will have little impact on the environment. Keep using peat moss for seeds.

Amending Soil

Peat has been a traditional additive for increasing the organic matter in soil, which in turn helps with drainage and improves soil structure.

This application uses large amounts of peat and does not make good use of peat’s special properties  because any organic material will work just as well. Since we produce lots of waste organic matter, finding an alternative is easy. Manure, compost, and leaf mold all work as well as peat and should be available from local sources. There is no good reason for homeowners to use peat for amending soil.

Commercial industries, making products like triple mix, use large quantities of peat and they might have trouble sourcing enough organic matter, but that problem can be solved with better management of waste organics. Agriculture and golf courses also use a lot of peat – they may have the same problem.

Potting Medium

A lot of horticulture peat is used for growing plants in pots and containers. The rest of this blog will focus on this application.

Peat Moss Alternatives for Potting Medium

The environmentalists say something like “There are many alternatives to peat moss, some of which are cheaper (often free) and may work better. In fact, the use of peat in horticulture is almost completely unnecessary.” The general population is starting to believe this story as well, but if we are talking about growing media as the application, it is a myth.

The search for an alternative to peat has been going on for some time, and the search continues. Nothing has been found that works as well as peat moss for a potting medium. Some products work in certain situations, but not others. Others products come close to being an alternative, but require the user to change their horticultural practices. That can be done in a nursery where they grow a lot of the same plants, but it is not a good solution for the homeowner who does not understand what changes they need to make for each plant they buy.

Roger Williams, head of science at the Royal Horticultural Society, which has been looking for alternatives for quite some time, said: “The bottom line isn’t whether peat free products are better or worse, but whether people can handle them in the same way. When you use peat free alternatives you have to be more careful in how you water plants. Peat is very forgiving and you can get away with quite a bit of under or over watering. But the alternatives are more vulnerable to waterlogging, and if they dry out they can become unusable.”, (ref 6).

Some products now offer a mix of peat and other alternatives. The main reason for this is that the alternatives just don’t measure up and can’t replace peat entirely.

Lets look at some alternatives that may be suitable on a commercial basis.

 Wood

Wood products usually consist of partially decomposed waste wood and can include wood fiber, composted bark, sawdust or wood (ref 2). These products have good drainage and low pH, but they require a higher nitrogen fertilizer than peat.

Wood products are usually inexpensive if they are made from locally sourced waste wood. One problem with wood is that the material is not consistent from batch to batch and you have no idea what chemicals might be included with the waste wood. In some cases, products are now made from trees harvested specifically for the purpose. That is probably not more environmentally friendly than using peat.

Anthony Witcher, a horticulturist at the USDA Thad Cochran Southern Horticultural Laboratory has this to say about the wood option, “Commercially, I think we could switch to 50 percent wood in our growing media. It could be an even higher ratio, but I think growers would have to address such issues as crop fertilizer and irrigation needs due to the reduced nutrient and water-holding capacity.” In most cases, a wood based medium would still contain a significant level of peat. (ref 7).

In Ontario, I am finding more and more landscape trees being sold in media that includes wood.

Yard Waste Compost

Municipalities and private companies are making compost from yard waste and industrial organic material ( sugar  cane fiber, olive and grape mash, rice and peanut hulls, cotton gin waste (ref 3)).

The resulting product may be seed free depending on the process and material used, and it usually has a low level of disease spores, but it is not sterile as some people claim.

Compost has a high nutrient level, making it unsuitable for pot culture on its own. It needs to be mixed with something else so that the compost level is no more than 30% (ref 2).

Composted Municipal Sewage Waste

Composted sewage waste, provided it is free of heavy metals, could be a suitable additive to potting media, but it is not accepted by the general population as a safe product. Even if it was accepted, this nutrient rich compost could only be used for a portion of the media and not as an alternative to peat moss.

Biochar

Biochar is a product that is produced by heating organic matter to high temperatures (300-500°C) in the absence of oxygen. The result is a very stable form of carbon (ref 4).

Biochar has been tested as an agricultural additive to soil and has shown mixed results (ref 3). Because of this and regulatory issues, commercial biochar is not readily available.

Even if further testing is positive it will probably only play a minor role in media as an additive.

Paper and Cellulose

A few products have been introduced to the market that are made from recycled paper and cellulose. Little scientific research has been done on them.

I contacted Pittmoss, one company that has been in the news a lot recently and asked for copies of scientific studies that compared their product to peat. They were unable to send any and none exist on their website.

Live Sphagnum Moss

The best peat for horticulture comes from sphagnum moss bogs. The sphagnum moss grows in the bog and accumulates over time forming peat moss. Over the last 15 years a number of studies have looked at the moss itself and found that it works just as well as peat moss, and in some cases it is even better (ref 5).

The harvested live plants, called sphagnum biomass, is a good alternative to peat, but it is not readily available. To change this, work has been done on developing sphagnum moss farming, where fields of sphagnum moss are grown specifically for harvesting. One of the ideal places to grow this moss is on old peat fields that have already been used to harvest pest. This has several environmental benefits. When water is returned to these fields to grow the moss, they stop producing CO2. Moss farming also uses land that is unsuitable for many other purposes.

Sphagnum farming is very new and can’t be considered an alternative at the moment, but long term, it might turn out to be the best alternative.

The video below shows a system for harvesting live sphagnum peat moss.

If the above video does not run try: https://www.youtube.com/watch?v=oIcMr8u1B5U

Coir

Coir is made from the husk of coconuts and is the waste product remaining after the coconut is harvested. It comes close to having the same properties as peat moss. Many people now claim that it is the ideal alternative to peat moss, but is this just another myth? I will have a closer look at coir in my next post.

 References:
  1. Envoronmentally-friendly Alternatives to Peat; http://www.eolss.net/sample-chapters/c08/e3-04-06-06.pdf
  2. Royal Horticuture Society – Peat-free Growing Media; https://www.rhs.org.uk/Advice/Profile?pid=441
  3. Growing Substrates Alternative to Peat for Ornamental Plants; https://www.researchgate.net/publication/281064937_Growing_Substrates_Alternative_to_Peat_for_Ornamental_Plants
  4. Biochar – A Home Gardener’s Primer; http://cru.cahe.wsu.edu/CEPublications/FS147E/FS147E.pdf
  5. Sphagnum Farming in Germany; http://mires-and-peat.net/media/map13/map_13_08.pdf
  6. Millions of Gardeners to be Banned From Using Peat; http://www.dailymail.co.uk/home/gardening/article-1339563/Millions-gardeners-banned-using-peat-protect-Britains-bogs.html
  7. Is Wood a Viable Media Component?:http://www.greenhousegrower.com/production/media/is-wood-a-viable-media-component/
  8. Photo source: KirinX

 

Robert Pavlis
Editor of GardenMyths.com
I live in southern Ontario, Canada, zone 5 and have been gardening a long time. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

I hope you find Garden Myths an educational site that helps you understand your garden better.

15 Responses to 'Peat and Peat Moss Alternatives'

  1. Magnus Palm says:

    Regarding your section about biochar, you mention that it “has shown mixed results”, but in the reference it is mentioned as a significant improvement to peat-only systems, especially when it comes to the proportion of marketable plants. The only “mixed results” I can find in the source is that it matters what material the biochar is produced from – but both types mentioned improves a peat-only system.

    Also, it seems very unlikely that there are any regulatory issues with using biochar in horticulture. It is not mentioned in the source,

    These comments are strictly regarding the use as a potting medium, as this was the subject in the blog post section.

    I don’t know if biochar can become a realistic replacement for some of the peat in horticulture, but it seems to have some interesting qualities. Main problems as I see it are price, poisonous smoke at production, high pH, and lack of knowledge/ research. It’s main advantage as a marketable product is probably the gimmick of being a carbon sink – people might feel like they are saving the climate by using biochar, as opposed to what they now feel about peat. That is sad, I think it has many other interesting qualities (or maybe I just believe the myths – I would love to read a myth-busting article about biochar!).

    • The comment about mixed results is for a biochar-only media.

      You say it produces poisonous smoke, but that there are no regulatory issues? I did not check into regulatory issues – it was mentioned in one of the papers I reviewed as a reason why not more product is on the market. It may not be a valid reason.

      I believe that the carbon sequestering feature is real – after all it is largely made of carbon and is stable. If you have facts disputing this – please let us know.

      • Magnus Palm says:

        Ok I see the part of biochar only systems now. That is probably not a good media for most plants!

        Yes, the traditional, cheap DIY method to create biochar/ charcoal produces lots of poisonous smoke, containing dioxins, carbon monoxide and more. But no, I don’t think this results in regulatory issues for it’s use as a potting medium. The product (biochar/ charcoal) is or can also be produced in more sophisticated, cleaner industrial plants with secondary combustion of the smoke. The product itself is not banned today (bbq charcoal), so it’s use as a potting medium is probably not banned either. Agricultural use on land is prohibited or regulated due to lack of knowledge of long term soil effects, but that is another matter. I still think the smoke is a problem, though. Even if the method is forbidden, it is easy and well known and would probably increase if the use of biochar would become widespread.

        Yes I also think that large scale use of biochar on farm lands, or even in woodlands, could be a carbon sequestration factor. But as potting media, I think the effect is small or even non-existing, due to low total volumes, higher density and lower compressibility than peat (resulting in higher carbon emissions from transport).

        Don’t get me wrong – I think biochar as a part of potting media is a great idea, mainly because it may contribute to its use on farm lands later. Do you by the way think the high pH could be treated with sulphur? For example a mix of biochar, peat and sulphur?

  2. Paul alaback says:

    In dry western landscapes peat as a soil amendment has a very different effect than compost or manure. It dramatically increases moisture holding capacity and also slightly acidifies the soil. It is particularly useful for acid loving plants like rhododendrons and azaleas

    • Compost will also hold significant water. The long term goal is to get the organic level higher so that it holds the water.

      I am looking into the ‘acidifying’ angle – I am not convinced that peat moss has a significant affect on soil pH except in sandy soils.Even if it is, using sulfur is a much better way to acidify soil, or you can do what I do with alkaline soil – don’t grow rhodos.

      • Paul alaback says:

        I agree sulfur can do same thing but peat is pretty easy to use and seems to last longer. Manure based Compost often increases pH due to all the salts. I Really see a difference for acid loving plants. Here in Colorado people grow blueberries in a buried bale of peat moss which works great. They die in composted native soil. So something is going on here. I know these plants have a unique mycorrhizal fungus that requires acid soil and allow them to access P and N.

        • Do you have a reference for ” peat is pretty easy to use and seems to last longer”?

          Composted manure is usually close to neutral pH.

          • Paul alaback says:

            This is my experience. I grew rhododendrons with peat and compost mixed into native clay soil. After 2 seasons leaves were yellowish so I treated with sulfur. Had to experiment a bit to get it right. In contrast I tried just growing blueberries in buried peat as recommended by local ag extension agent then adding acid plant fertilizer periodically. After three years this seems to work just fine, with good harvests after a year or so. Others have had good success after more than 8 seasons. I notice that Colorado State University extension also recommends peat for acid loving plants, and it has been tested in a number of restoration studies. So it seems like this is commonly recognized as a good way to grow these plant in basic or neutral soils. Still can’t find references on why peat works so well relative to compost.

  3. Kirk says:

    Great series. I am baffled about peat being an acidic amendment, when current research says peat, pine needles, coffee grounds do not alter soil ph? The BC scientist on YouTube who studied the pine said it was the bacteria dominated, somewhat anaerobic conditions of the pine forest that create the acidity, not the fallen needles which compost neutral. I assume the peat bog is similar.

    • I am looking at the acidifying capabilities of peat moss – I think most of that is a myth.

      Microbes can have an effect on soil pH, but the native minerals have a much stronger effect. Consider that rain has a pH of around 5.6 and it has been falling for millions of years, and the soil is still alkaline. Besides Pine grow just fine in alkaline soil.

      • Paul alaback says:

        Acid soils (podzols) mostly occur in cool climates with high rainfall. Cations get leached out making it acid. So I think climate rather than mineralogy is important. Pine needles have different effect in acid vs basic soils. (Most Useful in dry climates). Interesting questions.

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