Growing Carnivorous Plants Peat-Free
Many carnivorous plants grow in sphagnum peat bogs, and peat has long been considered the basic compost ingredient for most species. But if you’re thinking about growing carnivorous plants peat-free, where do you start?
Our Conservation Officer, Stephen Morley, has years of peat-free growing experience and has tested dozens of species in a wide range of alternative media. Here’s a summary of his advice about the different options.
Why Peat-Free?
Peat is cheap and it’s the natural growing medium for many carnivorous plants. So why is it no longer recommended?
Sphagnum Moss
What is it?
Sphagnum is a genus of mosses that grow in very wet environments. Peat (at least, the kind suitable for growing carnivorous plants) is mostly made up of slowly-decomposed Sphagnum moss that builds up very slowly over time in acid peat bog conditions. This makes Sphagnum moss itself very suitable as a replacement for peat for almost all carnivorous plants.
Unlike peat, which forms gradually over hundreds or thousands of years, Sphagnum moss grows rapidly in the right conditions and can be produced sustainably.
Usage
Sphagnum can be used for almost any carnivorous plant, and some growers use it extensively, although obtaining suitable quantities can be problematic. Sphagnum can be used fresh (live) or dried; dried moss needs to be rehydrated.
Live Sphagnum will continue growing and swamp seedlings and small-growing species, so consider dried/dead instead for these. Pouring boiling water over a pot of moss (before you plant!) usually stops it growing.
For smaller species you can whizz some moss up in a blender or coffee grinder, then mix this with perlite or grit, giving you a product very similar to peat.
Suitable for…
All species, but best for Nepenthes, epiphytic Utricularia.
I use it for most of my Drosera, Dionaea and Darlingtonia, loosely mixed with about 50% perlite.
Where to get it
Commercially-produced Sphagnum is harvested under licence or farmed. It is often available dried from orchid suppliers, or fresh as ‘hanging basket moss’ from garden centres — but do check that it’s Sphagnum moss, as other moss species are sometimes sold. Also available fresh and dried online or by mail-order from horticultural suppliers and garden centres.
You can grow your own Sphagnum quite simply, in a tray in the greenhouse or outside. Live Sphagnum is often used as a top dressing in plant pots, particularly for Darlingtonia and Heliamphora, and you can simply pull off pieces and stick them into the tops of other pots where they will grow.
Pros
- Good for most species
- Reasonably widely available
- You can grow your own, and as it is a living product you can potentially
grow unlimited quantities
Cons
- Can swamp smaller species if live
- Not as easy to process as a granular compost
- Expensive in quantity
Cocopeat
What is it?
Cocopeat is a byproduct of coconut production made from the husks of coconuts (coir). It is produced in the tropics, particularly Malaysia.
Coconut husks are composted and milled to produce a substance very similar to peat in structure, water holding capabilities, and pH.
Usage
Cocopeat can be used in the same way as peat, but with some important caveats.
Some coir products are washed in seawater, and it’s very important to select those that are not. Rinsing any coir product in rainwater before use is recommended. Some coir is ‘buffered’ with calcium to raise the pH — avoid this!
I first started using cocopeat in the late 1980s and I did keep my entire collection going on cocopeat for several years. I had variable results, probably because of variable products at the time — I think the quality of supply has improved now.
Suitable for…
An acceptable compost for certain plants such as mature Sarracenia,
Nepenthes & Pinguicula.
Good for Sarracenia seedlings, which are otherwise difficult to transplant into coarse composts.
Where to get it
Widely available from garden centres, online and by mail order as a peat-free compost alternative, but check that any mix you find doesn’t have added fertiliser. It’s often supplied in dry, compressed form and expands when watered (make sure you do this in a suitable container!).
Only a few suppliers, such as Fertile Fibre and Canna, guarantee salt-free products.
Pros
- Widely available
- A by-product that can be harvested annually, therefore arguably more sustainable than peat
- Similar properties to peat (acid, low nutrient)
Cons
- Not suitable for all species
- May need to be rinsed due to potential salt content (look for salt-free products)
- The coconut industry has its own sustainability issues regarding habitat destruction, pollution and loss of biodiversity
- ‘Buffered’ cocopeat has calcium added, avoid!
Coir Chunks
What is it?
Coir chunks are larger, less processed pieces of the same coconut husk material used to make cocopeat.
Usage
Although not often marketed as a growth medium, rinsed coir chunks are actually one of the better peat alternatives. Many species can be grown in pure coir chunks with no other additives such as perlite or grit required. Coir chunks have worked very well for many plants I have tried.
Some coir products are washed in seawater, and it’s very important to select those that are not. Rinsing any coir product in rainwater before use is recommended. Some coir is ‘buffered’ with calcium to raise the pH — avoid this!
Suitable for…
Particularly good for Nepenthes, Sarracenia, Cephalotus, Darlingtonia and Heliamphora.
Not recommended for Dionaea or Drosera as they will decline long-term unless you repot annually.
Where to get it
Quite widely available as a terrarium substrate, and online and by mail order as a peat-free compost alternative. Check that any mix you find doesn’t have added fertiliser. It’s often supplied in dry, compressed form and expands when watered (make sure you do this in a suitable container!).
Only a few suppliers, such as Fertile Fibre and Canna, guarantee salt-free products.
Pros
- Widely available
- A by-product that can be harvested annually, therefore arguably more sustainable than peat
- Similar properties to peat (acid, low nutrient), and supports Sphagnum growth
- Well structured, so does not need additives such as perlite or grit
- Breaks down slowly, so can be rinsed and re-used
Cons
- Not suitable for all species
- May need to be rinsed due to potential salt content (look for salt-free products)
- The coconut industry has its own sustainability issues regarding habitat destruction, pollution and loss of biodiversity
- Difficult to plant small plants in the coarse mix; use a top layer of finer cocopeat
Moorland Gold
What is it?
A proprietary range of composts made using peat that is extracted by filtration from reservoir water, Moorland Gold is produced by West Riding Organics as a by-product of the water industry. Water flowing from the hills of west Yorkshire collects particles of peat, silt and leaf mould due to natural erosion. This accumulates in filter beds and is dredged out to produce a horticultural product. The peat is not mined and doesn’t contribute to the destruction of peat bogs but is naturally present in the water, so it is arguably a sustainable source.
Usage
Moorland Gold can be used in the same way as peat. Because of the fine particle size and silt content it tends to be ‘heavier’ than normal peat, so it’s a good idea to mix in a bit more perlite or grit than you would use otherwise.
Note that there are multiple products in the Moorland Gold range. Ensure you select the ‘Natural Peat Alternative’ version without added fertiliser.
Suitable for…
Most species, as for peat.
Where to get it
Stocked by some garden centres and horticultural suppliers and available online.
Pros
- Similar properties to peat – suitable for many species
- Arguably a sustainable product
Cons
- Needs addition of grit or perlite to lighten the mix
- Used to have a reputation for weed growth – now heat treated?
- Not widely stocked
Thrive
What is it?
A proprietary peat-free growing medium ‘specifically developed for carnivorous plants’. The composition is a commercial secret but it appears to contain fine perlite, sand and what may be ground and composted pine bark, possibly along with other ingredients.
The producer claims that independent trials showed better growth of carnivorous plants in Thrive than those grown side-by-side in a peat/sand mix.
Usage
Use as per the product instructions.
I have had 2 mature Sarracenia planted in Thrive for several years now, they are doing well and I cannot tell any difference in growth between them and others grown in different composts. One of the pots has maintained Sphagnum growing on the surface which impressed me, the compost is obviously acid and low nutrient although I do not have any exact figures. Dionaea grow well in it and colour up nicely.
Suitable for…
I have used this for a few Sarracenia, Darlingtonia and Dionaea and they seem to have done well in it.
Where to get it
Online or from a few specialist growers.
Pros
- Similar properties to peat
- Pleasant to handle
- Convenient to use as pre-mixed
Cons
- Expensive
- Not widely stocked
- Not ideal for some species e.g. not recommended for Drosera
Melcourt Growbark Pine
What is it?
A relatively new addition to the peat-free options, this is made from milled pine bark and is an arguably sustainable by-product of the UK forestry industry.
There are various compositions in the range — it’s important to make sure you get the Growbark Pine version.
Usage
Use as with peat, generally mixed with perlite or grit.
Mike King at Shropshire Sarracenias has done a lot of work with mixes containing Growbark and has good results, although he has reported some inconsistencies which caused problems. I have also used it extensively and it worked well although I occasionally observed poor root development in Sarracenia.
Suitable for…
I have used this successfully with Sarracenia, Pinguicula, Dionaea and Cephalotus.
Not so good for Utricularia or Drosera, although tuberous Drosera seem to like it, perhaps because of the nutrient content?
Where to get it
Online or from a few horticultural stockists.
Pros
- Similar consistency to peat
- Pleasant to handle
- Relatively sustainable
Cons
- Not suitable for all species e.g. Drosera
- Some evidence of poor root development in Sarracenia
- Not particularly widely stocked