Pinguicula Substrates - Growing Media
By Pierre Gelinaud
Contact : a-miya@ii-okinawa.ne.jp
Home page : http://www.ii-okinawa.ne.jp/people/a-miya/eindex.htm
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 :
| 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 :Permalink
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 :Permalink
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 :Permalink
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 :Permalink
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 :Permalink
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 :Permalink
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 :Permalink
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 :Permalink
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 :Permalink
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+