These are plants that live naturally in bogs which because of their stagnant nature have a very slow breakdown of. The bacteria and other microbes that usually do this are not so active because of the lack of air. This is why the bodies of animals and plants are often preserved in peat bogs. Deprived, therefore, of their source of nitrogen carnivorous plants have adapted themselves to catch or trap their own usually in the form of insects. They are able to break down the insects’ bodies and absorb them into the plant. I find these plants great fun to grow. The cool greenhouse is the best place for most of them. They are best grown standing in a waterproof tray which in summer can be made most attractive. Build up the edges using logs or branches and fill the centre with peat. Plunge the pots of plants inside and finish off the surface with a layer of sphagnum moss which is not only attractive but is a good indicator that the conditions are right for the plants; if it stays alive so should they. Being used to acid conditions they will prefer soft or rain water. No fertiliser should be given as they will catch all they need. Potting should take place in spring and a of equal parts sharp sand and moss peat is ideal for most of them. Good ventilation especially in summer is essential. They should stand in water throughout summer but during winter allow the compost to become just a little less than soaking before putting more water in the tray. Seed sowing can be very successful with these plants. Seed compost should consist of moss peat, shredded sphagnum moss if available, a little sand but no fertiliser. Seed should be surface sown and covered only with glass or plastic and placed in a temperature of 18°C (65°F). Keep them in good but diffused light and take the cover off as soon as most seed has germinated.
Venus Fly Trap
By far the most well-known and popular carnivorous plant is Dionaea muscipula the Venus Fly Trap, which is unfortunate as they are not the easiest to grow. As a youngster I expected this plant to be large and quite dangerous so I was slightly disappointed to discover the reality which is a small rosette-forming plant which is rarely more than 8 cm (3 in) across but does form clumps. However, leaves can become up to 13 or 15 cm (5 or 6 in) long at some times of the year and the process by which they trap insects is amazing. On the insides of the open trap are several trigger hairs. When a small fly attracted by nectar lands on the leaf it has to touch the same hair twice or several different hairs before the trap will close. This is to prevent accidental closing which would take 24 hours to open again. To begin with the trap is lightly closed so that if a tiny insect not worth the effort has been caught, it can walk away. After a while the trap closes firmly on larger prey which by this time is well and truly caught. Acid and enzymes pour out of the leaf to digest the insect which is then absorbed apart from the hard parts such as exoskeleton and wings. A cool greenhouse and good light are required. Plants should not be covered with a propagating case or plastic as they dislike humidity.
In my opinion these are the easiest to grow. Sarracenia species and their hybrids form the bulk of these and I have found that they will overwinter easily in a frost free greenhouse provided they are not too wet. They need watching because they should not be allowed to dry out for more than a day or two either. In winter when there are no insects about the old pitchers gradually die down. Cut the dead tips down bit by bit so that the plant can continue to feed off the digested insects in the bottom of the pitcher. No new pitchers are formed at this time but the occasional leaf-like structure will grow just so that the plant can continue to photosynthesise. By spring a big bud will have formed at the centre of the plant and as the weather warms up new pitchers and strange ‘space age’ looking flowers appear. Doomed insects are attracted to the pitchers by nectar. Once inside they are unable to scrabble out and end up at the bottom with other insects. After they have died they will be digested and absorbed into the plant. I often cut a pitcher open at the end of the summer and am amazed at how packed with all sorts of insect remains it is. A favourite of mine is Sanacenia psittacina the Parrot Pitcher whose pitchers are reminiscent of lobster pots. Other genera in this group include Darlingtonia (Cobra Lily) and the rare Heliamphora nutans (Sun Pitcher). New plants are easily made by splitting up old plants in spring at potting time.
Tropical Pitcher Plants
Tropical conditions are required to do justice to these exotic plants in the genus Nepenthes as they require heat and humidity. The pitchers work very much in the same way as for Satracenia but they form at the ends of the leaves in a most curious way. The most horrid thing is when you are working amongst them and accidentally tip a pitcher over. It contains a foul smelling liquid usually with a few half decayed cockroach legs. These plants are best grown in hanging pots or baskets but must never be allowed to dry out. I used to keep them with tropical orchids and found that they benefited from a weekly application of orchid fertiliser which was also a foliar feed. Very tall straggly plants responded well to being cut hard back in spring after which they would branch nicely. The shoot could be used for cutting. The tip cutting should keep just its top leaf. Stem sections below this should be cut above a node at the top and below at the bottom with all but the top leaf stripped off. Dipping in fungicide and then the end in hormone rooting powder will prevent rotting and speed up rooting. Cuttings should be inserted into sphagnum moss and rooted in a propagating case with a bottom heat of 21-26°C(70-80°F).
These are delicate glistening plants which trap insects by attracting them to land on their sticky gland-tipped tentacles which dot the leaves. Escape is usually impossible and tentacles and leaves to some extent curl around the victim which is then digested and absorbed. Britain’s native Drosera rotundifolia and other northern hemisphere plants die back in autumn to a resting bud from which they will grow in spring. There are fine rosette-forming species from Australasia and South Africa but I find these more difficult to keep successfully over winter. Whereas a cool house is adequate for the others I think these really need warm temperatures., D. aliciae is a South African in this category. A lot easier from the same area are the stem-forming types such as D. Capensis but again a warmer temperature helps. The Australasian Pygmy Sundews really are delightful especially grown as many clumps to a pan. Also found in Australia are the fork-leafed sundews D. binata and its types which are large growing and correspondingly easier to keep over winter. Many sundews flower beautifully and give a fascinating display during summer. If you lose a lot of plants during winter, mostly due to a combination of damp and cold, do not despair. They are easily raised from seed.
I was fascinated when I found my first native Pinguicula vulgaris in Scotland. Pinguicula are perhaps the least spectacular of the carnivorous plants but do have very pretty flowers. Their method of trapping insects is similar to that of the sundews. Their leaves are covered with sticky glandular hairs although they are less obvious and impressive than those of the latter. Some, including P. vulgaris and P. grandiflora, produce winter resting buds. These are easier to grow than the Mexican species which just produce smaller leaves during winter but are perhaps the showiest.
Many carnivorous plants can be propagated bybut the first step is to learn how to grow them properly.