By Pierre Gelinaud 


Contact :

Home page :


The soils on which carnivorous plants grow in their natural environment are sometimes very specific and change according to the species and its geographical situation. Cultivation substrates are not so numerous. They all have their own physical, physico-chemical and biological properties. You'll find at the end of this page some pot cultivation principle, but now have a look at these different kinds of substrates with at first a table to give you a quick view of their properties :


Properties= --- very strong opposite effect, -- strong opposite effect, - soft opposite effect, 0 neutral, + have to consider, ++ important, +++ very important

Substrates Water retention Draining capacity Lightening capacity Chemical interactions Thermal insulation Risks
organic Peat moss ++ --- 0 ++ ++ --
Peat pellets ++ ++ ++ ++ ++ +
Sphagnum moss Live +++ --- ++ +++ +++ ---
Dried long-fibered ++ --- 0 ++ ++ --
Bark ++ ++ + + ++ ++
Osmonda fiber ++ ++ +++ ++ ++ --
Coconut fiber ++ ++ +++ ++ ++ --
Cork + ++ +++ 0 +++ 0
Mineral Perlites ++ ++ ++ ++ ++ +
Vermiculites ++ ++ +++ ++ +++ +
Expanded clay ++ ++ - + ++ +
Zeolites ++ ++ - +++ ++ ++
Ceramics + +++ -- + ++ +
River sands 0 +++ --- + + ++
Lava rocks + +++ 0 0 ++ 0
Pumice + +++ 0 0 ++ 0
Rock wool ++ --- 0 0 +++ 0
Gypsum + --- -- +++ 0 +++
Expanded polystyrene -- +++ +++ 0 +++ 0

Organic substrates :

Their common property is that they  interact on each other and with water. This will equilibrate and stabilise  the substrate and make it more similar to the natural soil of our plants. It could be dangerous too if you make a mistake when choosing the substrate. For  example a  "rich" substrate will provide too much mineral salts and poison our plants.  The most materials used as substrates are the following :


Peat moss :

It is composed of dead sphagnum moss (in the natural conditions of a bog). The fibrous one (the best) is powerful for water and air  retention. Only a very small part will decompose, so it's a "poor"  and acid environment that is convenient for our plants. This is the basic material for carnivorous plant substrates but used alone it is going to pack down and will loose its permeability. Its use is very common for agriculture in order to equilibrate soils that retain too much water (clay) or  soils  that can't retain  it (rocky).

Take care not to mix it up with black peat which comes from the decomposition of plants like "carex", "joncs", and some trees. Black peat is rich and unstable; it will decompose and provide  too much mineral salts.

"Blond" peat moss is coming from sphagnum moss that grows by making "steps" from few inches to few dozen of yards height (this is the peat bog). Sphagnum that is below dies that makes peat moss after it has been correctly  extracted. If extraction is not good there could be some decomposition and transformation. On the market you will find very different qualities of peat moss. The  best way to use it is to put the pot (with the new substrate) under water (fresh and pure water) and to make water go through it abundantly.  This should eliminate most parts that could have decomposed and unexpected mineral salts. I saw that for seedlings results are better with an old substrate than with a fresh one. With this treatment peat moss will provide acidity and humidity without any decomposition. A partially decomposed peat will provide good condition for algae (green or brown) that grow over pot surface. These  algae are very often basic and our plants won't like it even if it's not deadly.


Peat pellets :

This is peat especially made for aquariums, probably fired with other materials and condensed in a ball shape. From the same  manufacturer (Aquazone) there are different kinds with names like Amazonia, Africana... It depends on which environment you need. Of course for carnivorous plants we need the Amazonia type, as rivers of  the amazon basin are acid. The African ones have too much mineral salts like in the huge African lakes. This material brings the acidity of peat and because of its shape it's draining capacity is really better even if it packs down. If you want this result with normal peat moss you'll have to add another material. The weak point is that its exact composition is unknown... I try it and at the moment I've got no trouble. Another weak point is its price, really expensive.


Live sphagnum moss :

From Sphagnopsida class, the only kind is Sphagnum in which there are many species. The most common one is Sphagnum palustre. This plant like water and you can find it in bogs or near river and lakes sometime above 7000 feet. 

It is composed of many organic elements and is full of acids. There are organic acids, especially malic and citric acids and  also others  like fumaric, succinic and oxalic acids. There are also amino acids , aspartic, glutamic acids and carbohydrates (glucose, fructose, sucrose and some fructosides). It can stock too some elements from the environment like aluminium, iron, vanadium and beryllium.

Sphagnum are really acid and they could be a kind of food stock too. But the most important is that they act as a living water tank because of their high water retention capacity. Sometimes they could be considered as a filter but temporally. They can extract from water some alkaline mineral salts. Their last interest is that they prevent from mould (mold for American) and fungus. But there is a danger. They don't like to be in hot conditions, they will die and poisoned your plant. 

They are  widely used for growing young shoots as they provide acidity and protection against fungus. Some plants like sarracenias seem to grow faster on pure sphagnum and maintenance is very easy so it is much used for commercial production. Unfortunately it's very hard to find it at most of the plant resellers.


Dried long-fiber sphagnum moss :

Elements you'll find in it are the same as in live one but in rather smaller quantities because it has been dehydrated. It is a more neutral substrate (a little acid) with always a good water retention capacity. It  could be used alone or with other  media to light  it and make  it keeping  a higher quantity of water. 

It's a great medium but unfortunately commercial names are sometimes abusive (in the States). Some dehydrated sphagnums are not really Sphagnum palustre (sphagnum moss) but other moss that is not coming from peat bogs. The real commercial name is Sphagnum Moss. It is produced everywhere in the world : Australia, Canada, Germany, Irland, Japan, New-Zealand and United-States. It seems that the best quality is the one from New-Zealand, long-fibered and pure (clean). Take care as there is the same trap as with live one. They don't like high temperature with water in which they will rot and kill your plant.


Barks :

Generally it is bark from evergreen trees. Their are many different kinds but they always have some acids. It is used for draining especially with nepenthes. Take care of what you use because they can be full of mineral salts. Sometimes you can see some huge crystals of these salts that are not really good for most of carnivorous plants. I don't use it too much as I found a better medium (see below). Barks for orchids seem to be of a good quality for our plants but there is always a risk.


Osmonda fiber :

This is a family  of  ferns, Osmondace. A typical species is Polystichum thelypteris) that grows on  the edge of peat bogs. They retain water but not as much as sphagnum and provide some acids too. They have  also some mineral salts , 0.22% of P2O5 and 2.03% de K2O, nothing very dangerous for our plants. They contain water, 13.76%, nitrogen (N), 0.19% and carbon as in every organic material. The most important is the  pH around 6.2 with a strong capacity of exchanging cations (+) that, with water, makes an acid neutralising solution. This material is fibered and could be cut by hands. It's between bark and cork. I use it for draining and lightening substrate and very often I put it in the bottom of the pot to prevent the draining hole from filling in. It does with nepenthes in the whole substrate and I really prefer it to bark.


Cork :

It's not really bark as bark is alive and not cork. All trees have bark but not all produce cork. It's like a secondary bark composed of hydrophobic dead material. Cork is very often used for phonic and thermal insulation but it can be used in the same way as vermiculite to drain and lighten substrate. Unfortunately it's rare in shops in a usable shape for us and then it's expensive.


Mineral substrates :

Most of mineral substrates that are used as carnivorous plants substrates are mineral clay which basic structure is composed of silicon and oxygen. They are all  crystallised silicates to different shapes and with numerous elements like aluminium, calcium, iron, sodium, potassium... Some of these substrates are natural ones others are processed.  The properties of each one are very different. It depends on cathions (Al3+, Fe3+, Mg2+, Ca2+...) and especially on there crystal structure. These cations are important when you choose this medium as silicates will decompose themselves in water and slowly release free cations. Some of them like Fe3+ or Mg2+ could be good +, others like Ca2+ or Na+ are dangerous for carnivorous plants. It depends on the plant too.


Perlites :

It's a natural lava rock of silicates (or a mix of rocks) that has been  heated over 2200F (1200C) and cooled in many drop like  pellets more or less big. Sometimes big ones are broken in small pieces that make them look like natural rocks. Composition as  written  on the package is the following: SiO2 75,41%, Al2O3 12,85%, Fe2O3 0,64%, MgO 0,36%, Na2O 3,70%, K2O 4,55%, CaO 0,82%. This medium has some calcium, potassium and sodium that are alkaline. It could  be harmful for  plant that really like acidic environment as some utricularia, byblis and others... But they won't be completely free in water and anyway it will be at low level that could be accepted by carnivorous plants.

This substrate is very light and you can break it with your fingers. It will slowly and partly dissolve in water. Its lightening capacity is very good and so it is often used with peat moss in all possible mixing proportions.


Vermiculites :

This medium is of the phyllosilicates' family, it's a trioctaedric smectite which formula is : (H,Na,Ca1/2)x(MgxAl2.x)Si4O10(OH)2. Composition is  nearly the same as perlite but its crystal structure is very different. This structure is made of thin atom sheets linked together by cations. This link is not very strong especially for vermiculites in which many Si4+ cations have been replaced by Al3+ cations. Because of the lower electric level of each atom sheet these sheets can be easily separated. One consequence is that cations can be exchanged easily too with environment. These cations can be : H+, Na+, Ca2+ and Mg+. This could be good or bad, it depends on cations and plants

It's not a neutral medium. Cations exchanges will make the environment more stable but with a loose of acidity (not too much). Vermiculite you can find on the market has been dehydrated at over 570F that make it very light. It is used to lighten the substrate. Its size and shape can be different from one to another that make it more efficient (in my opinion) than perlite.


Expanded clay :

Attapulgits are lathed minerals. Composition is nearly the same as vermiculite but structure is made of atom ribbons linked together. This link is due to Mg2+, AL3+, Fe3+ cations. These differences and process at very high temperature give to expanded clay some really different properties. It's a neutral medium (about pH) and it will not decompose a lot. Generally its shape is big balls so we can only use it around pots to retain water and have it less evaporated. You can find them in small size too but it's difficult. There are some natural clay that have not been processed. It will mix in the substrate because of water. It could be   useful with draining substrates in which it's difficult to retain peat. Clay will act like glue and protect roots from "moving" substrate. I use it with pygmy droseras and  sarracenias.


Zeolites :

These are hydrated tectosilicates which crystal structure is three-dimensional. It's like many cages connected by tunnels. Because of this they have outstanding properties. They have high capacities to retain many different kinds of molecules among which is water. They are natural filters and are used as for many purpose. Most common zeolites are Analcime ([Si2AlO6]Na,H2O), zeolite A (Na12[(AlO2)12(SiO2)12],27H2O), Prehnite (Ca2,Al[AlSi3O10](OH)2), Natralite ([Si3Al2O10]Na2,2H2O)... Perhaps you have seen that there are alkaline cations sometime at a high level. Keep it in mind! Their high exchange capacity makes their chemical behaviour somehow complicated and unpredictable. At first in substrate, when it's dry, they will absorb mineral salts but later they could give it back or exchange it with others in water.

So it's very difficult to be sure of anything. Their use is very interesting as filter medium for terrarium or in water around pots. In this case they should be changed regularly. Using it as a part of substrate is not a good idea, it depends on plant and zeolite type. The one I use could be used on that purpose as you can see (composition writen on the bag): SiO2 73,30%, Al2O3 11,68%, Fe2O3 1,15%, MgO 0,18%, Na2O 2,01%, K2O 3,6%, CaO 0,68%. Alkaline cations are at low levels. In substrate they will drain it more or less (it depends on size) but the most important is its "filter effect".


Ceramics :

This is the name of a huge family, any silicate that has been fired. I will speak of the one I bought that was made for aquarium soil. The shape is small cylinder about 0.08 inches of diameter and 0.16 inches long. Composition written on the bag is as followed : SiO2 78%, Al2O3 12%, Fe2O3 5%, K2O+Na2O 1%. Basic composition seems to be  close to perlite and vermiculite but there are two main differences : There is no calcium and sodium and potassium are at very low levels that is very good for acidic substrates. Finally iron level is rather higher than in other mediums that could be really healthy for our plants.

Its density is nearly the same as sand. It will be used to drain but not to light. It seems to have similar properties as australian laterites and so could be very useful to grow pigmy sundews or byblis. Keep in mind that I speak only of this ceramic, others could be different!


River sands :

As you can imagine there are many different kinds. The only kind that is good for our carnivorous plants is a sand without any mineral salts with Ca, Na, K ... Generally some river sands are convenient, it depends where your live and the kind of river. In France there are "sable de Loire" and "sable de Moselle". They have been washed but they need to be more washed as they always contain a little part of clay, dead shells and others. At first they will release substances in water but after a while they are near  neutrality . Unfortunately most of river sands are full of calcium so take care of what you choose. You can use  also quartz sand really neutral but it will hurt roots, as it is sharp. In any case these mediums are used to drain.


Lava rocks (pouzzolanes) :

This is volcanic ash. It comes from magma expulsed of a volcano crater. Because of the contact with air it becomes solid and lies around volcano. At the beginning this rock is said 'active' as its structure and sometime its composition will change. After a while (very long time) a slow crystallisation occurs and finally after many centuries we have some neutral lava rocks as we use it. Composition can be very different but anyway it's neutral so we have not to care about it. These rocks are very light and porous so it's very useful to drain and light substrate and they can retain peat too. The environment where they come from is important because they are porous and could contain numerous 'things'. Even if you wash it well there will be impurities left. Its better if they come from acid environment.


Pumice :

They are  of the rhyolitesfamily and come from lava flow. They are only near volcano where they can cover a wide area and as deep as many hundreds yards : 75 000 sqft at Yellowstone, 267 000 sqft in New-Zealand and in Europe 26 700 sqft at Mont-Dore (France).  This rock is neutral and porous like lava rock but its  colour is grey. I have no information about its composition but due to the condition of its formation it could contain numerous metals sometimes rare ones. It is used in horticulture with orchids. In this shape you can use it as well for carnivorous plants especially with Nepenthes.


Rock wool :

It comes from lava rocks smelted (with glass you will have glass wool) and cooled in a shape of fibber. It is completely neutral and very light. It has a good water retention capacity and as there is no chemical interaction with roots disease risks are very low. You can easily control what you give to feed your plant as everything will come from water and not from substrate. So it is used also as reproduction and growing substrate for commercial purpose. After a while I think this substrate is not suitable because rock wool will never provide anything to our plants.


Gypsum :

It's a mineral clay, more exactly hydrated calcium sulphate(sulfate), CaSO4,2H2O. It's very common in nature. It is used of course with plants that like calcium as some pinguicula do. It's not always easy to find it in a shop so the easiest way is to crumble some plaster even if it contains other elements. Plaster ready to use is principally bassanite, half-hydrated calcium sulphate CaSO4,H2O. When fully hydrated it becomes hard (and warm) forming gypsum, plaster. Then you can use it in substrate to provide calcium. Be aware that there is an un-hydrated calcium sulphate CaSO4 obtained by firing gypsum over 575F and that can't be hydrated again. So this one is not directly usable by plants.


Other materials :

Expanded polystyrene :

This one is well known and used everywhere more often for thermal insulation. In plant's pot it drains and lights substrate and stays perfectly neutral. I use it with nepenthes in whole substrate and at the bottom of pots with other plants. Its use is clear and easy, no problem.

Some principle :

Mixing possibilities are infinite so I won't give any particular formula. You have to do with your kind of plant, its natural environment and moreover and especially the environment you can provide : Watering, size of pots ...

Though some carnivorous plants grow in specific soils you can grow them without any problem with completely different substrates, hopefully! Anyway even if you provide the same soil as in natural environment, some other parameters will be different.

- Thermal insulation and stability in culture have nothing in common with the thousand tones of soil surrounding a  wild plant. For example Darlingtonia californica cultivation often need a cooling system for the pot.

- Water saturation in pots depends on its depth and will be different like the aeration. Capillary action will be strong in pots. That means substrate will saturate at a higher level than water surface.

- Stability of all parameters is lower than in nature. Our plants will have to bare more variation in temperature, pH, aeration, hygrometry, sun exposition and water composition.

When you choose a substrate you have to identify  the most important parameters  of the natural environment to follow them the best you can considering pot cultivation. Unfortunately information about natural environment are often difficult to find. Hopefully if you follow some basic conditions you will be able to obtain good results. Substrate could have nothing to do with natural soil and be perfect for our plants. Carnivorous plants have some adaptation capacities. With "easy" plants like venus fly trap or some drosera you just need to provide fresh water free of calcium, a substrate without mineral salts too and sunlight. The more conditions you have to respect the more the plant will be "difficult".

With these "difficult" plants you need common sense. Different mediums have different effects. You'd better choose by looking at these differences. An example: Using bark to drain substrate is very good with nepenthes but not so  good for pygmy drosera with which rocks or sand do better because there is no need to light substrate. Size is important too especially for draining capacity that will change a lot between a half-inch lava rock and a few inches one. I say it one more time use your common sense. Don't try mineral substrate with an epiphytic plant and so on... Finally you have to do with what you find at shops around you and it's not always easy.