This post illustrates that many Carnivorous Plants grow in habitats so similar to one another that cultivating the plants is simplified by an understanding of a few general facts. Carnivorous plants typically inhabit wet, low-nutrient soils through which water may be slowly moving. This moving water usually carries away what minerals there are in the soil, which explains why it tends to be low in nutrients. The soil is often sandy, with a ground cover of patchy mosses such as sphagnum, which turns into peat as it ages. The habitat is often sunny, and the few trees are commonly stunted by growing in the infertile soil. Pines or other evergreens, whose needle droppings may further add to the soil’s acidity, are the most common trees in such habitats. Grasses are also common. In short, a wet, low-nutrient, sunny environment is preferred by most CPs. The only major difference between habitats, usually, is the climate.
Soils
Specific soil recipes will be offered in the section on genus cultivation. Here I will discuss the individual ingredients used in most artificial soil mediums for carnivorous plants.
Sphagnum Peat Moss
Peat moss is probably the most important soil ingredient for most CPs. It must always be sphagnum peat moss; the word “sphagnum” must always appear on the moss packaging. Peat moss is usually sold in packages ranging from small bags to large, dried, bricklike bales. It is commonly of Canadian, Irish, or German origin. It is a fibrous moss, with a consistency close to that of a fine sawdust, and from light to dark brown. It is available in most general nurseries, usually as an additive for garden soils. It is what many carnivorous plants grow in naturally. Sphagnum peat is very acidic, usually with a pH between 3 and 5. (On a scale of 1 to 14, a pH of 7 is neutral.) It can hold as much as ten times its own weight in water.
Peat moss should be broken up until it is similar to sawdust before it’s used, with all lumps and clods gone. It should then be mixed with water until it resembles a soft, wet mud. Then it is ready for use. Avoid sedge peat or Michigan peat, which are entirely different substances. If the package doesn’t say “sphagnum,” don’t use it! One problem with the commercial sale of sphagnum peat moss is the addition of fertilizers such as the Miracle-Gro brand to the moss, because CPs need low-nutrient conditions to thrive. Read the labels carefully and avoid any peat to which fertilizers have been added.
Long-Fibered Sphagnum Moss
This is a problematic soil ingredient for two reasons. The first is that what is sold in most nurseries is often not long-fibered sphagnum moss at all, but decorative green moss or “Oregon sheet moss.” “Sphagnum moss” has unfortunately become the generic term used for any dried, fibrous moss used in horticulture.
Decorative moss is often used as a basket liner or topdressing for potted plants, as is true sphagnum. Worse, I have seen packages of decorative green moss actually being sold as sphagnum moss. I have seen many CPs killed because decorative green moss was mistaken for true sphagnum. Further complicating the situation is the confusion between long-fibered sphagnum and sphagnum peat. Sphagnum moss, usually greenish or reddish, grows along the surface of the moss bed in a typical bog. It grows in long, ropey strands, with the growing head of the strand at the bed’s surface.
These strands can be rather lengthy, extending deep below the surface of the growing tips. Only the first 6 to 7 inches (i5-18 cm) at the surface are colorful and alive. Underground, the moss turns brown, and a couple of feet (0.6 m) below it decomposes into sphagnum peat moss. The peat may extend quite a way underground and may be hundreds of years old. Testifying to the sterile conditions of the moss is the fact that centuries-old, virtually unspoiled human bodies have been found deep within peat bogs in Europe.
Long-fibered sphagnum usually refers to the dried, ropey strands collected from the moss bed’s surface. Sphagnum peat is the decomposed moss harvested from deep underground. In soil recipes for most carnivorous plants, the more reliably labeled peat moss is the preferred ingredient.
For some carnivorous plants that prefer long-fibered sphagnum moss in their soil recipies, such as the Nepenthes, high-quality moss from New Zealand or Chile is the best and available most often through CP or orchid specialists. In the United States, what is known as “domestic” sphagnum, harvested in states like Wisconsin, is a less expensive type that often includes twigs and leaves. While inferior as a soil, it is excellent to cover the holes of drained pots to keep peat soils from slowly leaking out.
Live Sphagnum Moss
Living sphagnum is a beautiful moss—lush, billowy, and colorful when well grown. Many carnivorous plant growers love the sight of bright green or red sphagnum covering the soil surface of a potted CP, even if it isn’t used throughout the whole pot. Live sphagnum can be induced to grow as a topdressing to peaty, wet soils, although sometimes with difficulty.
The drawbacks to live sphagnum are many. First, it is difficult to obtain commercially. Second, it grows slowly. Third, when it does grow, it will easily cover up small plants like Venus flytraps, causing them to rot. Fourth, it is difficult to maintain. Hot sun will burn the growing tips, and the lightest application of fertilizers or minerals can cause algae growth and death to the moss.
Milled Sphagnum
This is dried, long-fibered sphagnum moss that is shredded to the consistency of fluffy, coarse sawdust. Usually sold as a medium on which to germinate seed, and resistant to the dreaded damping-off fungus that attacks seedlings in damp environments, it would be excellent as a peat substitute were it not so expensive.
Sand
All sand used in soil recipes for carnivorous plants should be sand that has been well washed. Nurseries and garden centers usually have washed sand available for use with potted plants. Washed “play sand” meant for use in children’s sandboxes is also good, and is often sold in plant nurseries and home supply stores. Avoid self-collected beach sands or river sands, which are often contaminated with mineral salts.
Perlite
Perlite is a mineral rock that is heated until it expands, creating a lightweight, granulated soil additive that will hold both water and air. Usually white, it is available at garden centers. Fine and medium grades are preferred for most CPs. Commercial nurseries generally prefer to aerate the soil in potted plants with perlite rather than sand, because sand is very heavy and leads to high shipping costs. However, most perlite is also slightly alkaline (pH of around 8), so never use more than 20 percent in the soil mix for acid-loving CPs.
Pumice Another lightweight, airy rock used in horticulture, pumice is usually gray.
Lava Rock
This volcanic rock is reddish brown, and available at most garden and landscape centers.
Vermiculite
This is a mica, processed similarly to perlite and serving a similar purpose. It is usually golden-brown. Since most vermiculites contain some minerals (such as magnesium and potassium), and it breaks down, turning to mush, I no longer use it for CPs.
Orchid Bark
Available at most garden centers, this is usually the bark of evergreen trees. Popular for orchids, it is helpful in soils for Nepenthes, among other CPs, and makes a decorative topdressing on peaty soils used for plants such as Sarracenia. A fine-grade bark is preferred by CPs.
Shredded Bark
Similar to orchid bark, this is shredded to the consistency of confetti.
Osmunda or Tree Fern Fiber
This natural material is usually blackish brown and has a consistency not unlike that of broken toothpicks. It is used to aerate soils.
Rock Wool
This interesting substance is sometimes used for plant propagation, especially in cases where stem cuttings are used. Rock is liquefied and spun into lightweight fibers, then usually molded into small bricks. Difficult to find in the general nursery, it can sometimes be obtained through specialty houses. Bricks of rock wool retain moisture, and stem cuttings of Nepenthes root well in it. The entire brick is later planted in soil.
Coconut Soils
In recent years cow peat, or coir, has appeared on the market, produced as a by-product of the coconut palm industry. I had disastrous results with this product when it first appeared on the market—primarily due to salt contamination. While some cow peat or cow chips are now claimed to be heavily washed in fresh water and some growers use it, I don’t.
Water
This is probably the single most important issue concerning the cultivation of carnivorous plants. Generally speaking, CPs require water that is low in dissolved mineral salts, and they usually need lots of it. Dissolved minerals are usually indicated on analysis as p.p.m., or parts per million, or t.d.s., meaning total dissolved solids. Water used for the cultivation of carnivorous plants is safest for the plants when it is below one hundred p.p.m. of dissolved solids, and the lower the better.
It is the use of hard, mineral-laden water that most often causes carnivorous plants to decline in cultivation. Since the majority of CPs are grown in basically undrained conditions, constant use of hard water continually adds minerals to the soil. Since CPs are adapted to grow in low-mineral soils, roots will begin to rot and the overall health of the plant will suffer when dissolved minerals are left behind as water evaporates or is absorbed by the plant. The more you water, the more minerals you add to the soil.
