Potting or Growing Medium for Venus Flytraps
Venus Flytrap soil should be freely draining but moisture retentive. Although those are characteristics of many garden soils and commercial potting mixes, common garden soil or dirt from one's yard will almost always kill a Venus Flytrap within days or weeks, and potting soil that other plants thrive in will almost certainly kill a Venus Flytrap. This is because the Venus Flytrap, like many other carnivorous plants, has roots adapted to and requiring a "soil" or growing medium that contains almost no nutrients nor soluble minerals.
In nature, Venus Flytraps grow in sandy soil that has very little organic material, has almost no fertility, and is somewhat acidic. Sand dries fairly quickly, and the natural soil of Venus Flytraps often looks fairly dry on the surface. But the natural habitat of Venus Flytraps is coastal with a high water table (the ground water level is often within a few feet of the surface) and fairly frequent rain. Both of those factors help to keep a very sandy soil moist, as water continuously wicks upward by capillary action from the ground water below the surface, and occasionally falls onto the surface as rain.
Venus Flytraps growing in a characteristic sandy, low-nutrient, acidic natural soil with a high water table
However, Venus Flytraps do not like to be in soil that is wet all the time, or too wet for too long. In those wet conditions Venus Flytraps will often develop fungal or bacterial infections in time that can lead to rot or death. When we grow Venus Flytraps in containers in our own conditions, we need to create a "soil" (a growing or potting medium) that retains moisture but does not stay soggy or too saturated with water for too long, and which incorporates plenty of air into the soil.
Standard Venus Flytrap potting mix ingredients: silica sand, sphagnum peat moss and perlite
The most common ingredients for a Venus Flytrap potting medium are sphagnum peat moss, silica sand and perlite. Sphagnum moss grows readily and abundantly in cool to cold regions, or temperate regions that have a pronounced winter or cool season. Sphagnum peat moss is dead sphagnum moss that has partially decomposed, and has a dark brown color. Sphagnum peat moss is distinct from "long fiber sphagnum" and live sphagnum moss, all three of which are described in the VenusFlytrap.info glossary, here: sphagnum moss.
Sphagnum peat moss is very moisture retentive (it absorbs and holds a lot of water) and is acidic (contains tannic acid, a preservative that inhibits fungal and bacterial growth), but it is not ideal to use by itself as the only ingredient in a potting mix, because it can compress in time and can remain soggy and saturated with water for too long. Silica sand or perlite added to sphagnum peat moss reduces the total amount of moisture retentive material in a growing mix (because neither sand nor perlite absorb or retain much water) and therefore help the medium to dry more quickly.
Sphagnum peat moss, the standard base for Venus Flytrap potting mixes
Silica sand is sand composed almost entirely of silicon dioxide, or quartz. It is different from most river or beach sand. For a Venus Flytrap potting mix, only silica sand should be used, never river or beach sand nor sand from any other source, unless it is known to be almost pure silica. Silica sand is an excellent addition to sphagnum peat moss to make a potting mix that incorporates air into the soil as well as retaining water, is freely draining as well as moisture retentive, a well balanced mix. Many growers of Venus Flytraps use a growing medium composed of equal amounts by volume (not by weight) of sphagnum peat moss and silica sand. In addition to natural silica sand, artificial silica sand is also available and is fine to use in a Venus Flytrap potting mix. More information about silica sand.
Silica sand, recommended for Venus Flytrap potting media
Perlite is often used as an alternative to silica sand (when silica sand cannot be found). Perlite is a man-made product created by heating volcanic rock to a very high temperature. Perlite is extremely lightweight and composed mostly of air spaces (bubbles that form when the volcanic rock is heated).
Perlite, used as an alternative to (or in addition to) silica sand in a Venus Flytrap potting mix
Common Venus Flytrap Soil Recipe
- 1 part (by volume, not weight) of fluffy, decompressed sphagnum peat moss
- 1 part sand or perlite, or a mixture of the two
Warning: use only pure ingredients with nothing added. Any perlite or sphagnum peat moss (or other ingredients) used to make a Venus Flytrap potting medium should be pure (consist only of that material). Miracle-Gro brand perlite and sphagnum peat moss (for example) often have plant food added which makes them unsuitable for use with Venus Flytraps and other carnivorous plants. Avoid Miracle-Gro brand and read the bags or other packaging carefully to assure yourself that the perlite or sphagnum peat moss has nothing added.
Alternative Potting Mix Ingredients
Alternatives or Additives to Sphagnum Peat Moss
Sphagnum moss is a common garden soil amendment (additive) and is used by many people for many purposes. It is often mined and used faster than it grows and replenishes itself, which causes sphagnum peat moss to become more scarce and more expensive over time. For this and other reasons (including simple curiosity), people have experimented with and continue to try new or alternative ingredients to use in carnivorous plant potting mixes, either to supplement sphagnum peat moss or to replace it.
Alternative ingredients and experimental additives, to use instead of or in addition to sphagnum peat moss, include—
- Pine needles, or needles from other evergreen trees such as fir
- Evergreen bark pieces, sometimes sold as "orchid bark" for use in orchid potting media
- Coir, which is coconut husk pith, a byproduct of the coconut fiber industry. Coir must be desalinated before use (soaked and drained repeatedly to remove mineral salts and other soluble material). More information about coir.
Coir mediums are not as acidic as sphagnum moss mediums, because sphagnum moss produces tannic acid and is naturally antibiotic (which is why some dead people from centuries ago are still found, with skin and internal organs still present, in peat bogs in Europe, England and elsewhere, and why tannic acid is used to tan animal hides to make leather). Although young adult and mature Venus Flytraps usually grow well in a medium containing only desalinated coir and silica sand, a coir medium can be acidified by using pine needles and evergreen bark in the mix with the coir and the silica sand (or perlite, or crushed lava rock, or bits of styrofoam, or—).
As a personal grower's note, the primary problems I've had with coir have been when using it as a potting medium for very small Venus Flytraps. Coir is so spongy and springy that after watering, the mass of growing medium heaves upward as it dries, often partially uprooting tiny Venus Flytrap seedlings or at least making it difficult for them or other young plants to establish their first, or first several, roots.
In addition, because coir is not very acidic (doesn't have the natural antibiotic properties of sphagnum moss), fungal growths can occur on the surface of moist coir more easily and frequently than on sphagnum peat moss. The upper surface of coir exposed to sun and air does dry quickly, however, which in most climates and conditions helps to prevent flushes of fungal growth on the coir medium.
If coir is used in a growing medium, it must be desalinated first. Please read about how to treat and desalinate coir before use.
Alternatives to Silica Sand or Perlite
Silica sand or perlite in a traditional carnivorous plant mix serve to break up and aerate sphagnum peat moss, which can become quite compact and dense, and to displace some of the peat moss, causing the entire mix to be less moisture retentive, which is a good thing because sphagnum peat moss by itself can hold so much water that it can become soggy and stay too wet for too long and threaten the health of the plants, encouraging fungal or bacterial rot, including a very destructive anaerobic bacterial rot.
However, many people have difficulty finding pure silica sand, and some popular brands of perlite (such as Miracle-Gro) contain fertilizer which can harm Venus Flytraps and other carnivorous plants. Therefore, some interesting and creative alternatives to these two ingredients have been used and experimented with. The main goal is to find something that acts like silica sand or perlite, that is to say, is inert (won't dissolve and adds no minerals or other material to the rest of the potting mix) and sufficiently breaks up the sphagnum peat moss (or the alternatives to sphagnum listed above) to allow the potting mix to drain more freely, incorporate more air, and be less moisture retentive (dry faster and not stay saturated with water for too long). Some of these alternatives to silica sand and perlite include:
- Chopped styrofoam (polystyrene) packing "peanuts"
- Aerolite, polystyrene pellets often used in orchid mixes
- Plastic BB's, the small round pellets used in BB guns
- LECA (lightweight expanded clay aggregate), a clay pellet product created by heating clay in a kiln so that it partially melts and the gasses that form inside create numerous air pockets that remain as it is cooled
- Crushed lava rock, a natural material that is very light and has numerous air pockets within it
— Stephen Doonan, FlytrapRanch.com