Carnivorous plants

An ever popular group of plants with children, carnivorous plants lend an element of curiosity to windowsills, greenhouses, containers outdoors and in the open garden where they have a place in both traditional and contemporary garden design.

Carniverous plants

Quick facts

Common name Carnivorous plants
Botanical name Cephalotus, Darlingtonia, Dionaea, Drosera, Nepenthes, Pinguicula, Sarracenia
Group Herbaceous perennials and evergreens
Flowering time In the growing season
Planting time Spring
Height and spread Various
Aspect Sun to shade, depending on species
Hardiness Tender to hardy, depending on species
Difficulty Moderate

Cultivation notes

Carnivorous plants come from a range of climates including tropical Asia, Australia, temperate Europe and from areas as diverse as Mexico up to Alaska. Their requirements are very variable.

Carnivorous plants trap and extract food from other living organisms to supplement the lack of nutrients in their habitats. They have food collection mechanisms that include traps, pitchers, sticky pads or suction techniques.

Composts

It is important to select the correct compost formula for each genus. All of them dislike nutrients in the compost but some prefer free drainage while others need boggy conditions. Ready-made potting composts are not suitable, but the ingredients to make up suitable composts should be easily obtainable from garden centres or mail order suppliers.

Carnivorous plants have evolved in association with peat bogs and have always been thought to grow best in peat. However, some growers have undertaken their own trials with peat-free alternatives and are now sharing their successes.

Peat-free carnivorous plant potting mix

  • One part perlite
  • One part fine or coarse Cornish grit (lime-free)
  • Two parts fine milled bark (obtainable from Melcourt)

Mike King of Shropshire Sarracenias, has trialled a number of mixes and found one so good that he grows all his National Collection of Sarracenia in them. The mix is given above.

Peat-free Venus fly trap potting mix

  • Five parts sphagnum moss
  • Three parts horticultural (silica) sand
  • Two parts perlite

Mix as recommended by the American site flytrapcare.com.

Feeding

No additional feeding is required for carnivorous plants. In exceptional circumstances, a quarter strength feed of a houseplant fertiliser can be applied as a mist spray to seedlings and immature plants of Sarracenia, Darlingtonia, Nepenthes and Pinguicula. Spray lightly using a fine spray, no more than once a month, in the early morning.

Water and humidity

Rainwater is most suitable for carnivorous plants. Tap water contains chlorides and fluorides and many hard tap waters contain high levels of calcium making it too alkaline for carnivorous plants. Domestic water softeners simply exchange calcium for sodium, and the sodium can build up to toxic levels over a period of time. Distilled water is a suitable though expensive alternative but de-ionised water has similar properties to water treated by a water softener. If rainwater is scarce, tap water may be used if boiled and subsequently cooled, but the compost must be replaced within six months.

Water from below throughout the growing season, by standing plants in a saucer containing approximately 2.5cm (1in) of water. During winter, water from below, then discard the excess. Pinguicula is an exception and it should always be stood in water. Never fill pitchers with water, they will regulate the levels themselves.

Choose a large saucer filled with pebbles or gravel, keep the water level below the surface of the gravel and stand the pots in the middle so that a relatively high humidity can be maintained.

Hardy carnivorous plants

Grow these hardy forms in a bog garden, created using a perforated pond liner and compost mix of sphagnum moss peat and washed sharp sand. Five parts moss to one part sand is ideal.

In the rock garden at RHS Garden Wisley, Sarracenia flava, S. psittiacina, S. catesbaei, S. gilpini, S. oreophilia, S. leucophylla and S. rubra survive winters unprotected.

Drosera (sundew)

As well as the more tender sundews, there are several suitable for growing outside. Drosera rotundifolia (British native) and D. filiformis var. filiformis are suitable for growing outdoors. Plant in good light, but not direct sunlight.

Like all sundews, they have modified leaves covered with red hairs that secrete a sticky substance for catching their prey.

Grow in equal parts by volume sphagnum moss peat and washed sharp sand.

Propagation: Propagation is from seeds and by leaf or root cuttings.

See the Sundew Grow Guide for more specific growing requirements.

Pinguiciula (butterwort)

Pinguicula grandiflora and P. vulgaris are British natives. They and their less hardy relations are plants with fleshy rosettes of light green leaves, covered with dew-producing glands. Leaves are produced in spring and most species die back or die down completely in autumn. Large, showy flowers are produced. Some species are hardy; others need greenhouse conditions.

Grow in a mixture of equal parts by volume sphagnum moss peat and washed sharp sand with a little added leafmould is suitable for most species. Use shallow pots.

In the garden butterworts can be grown at the edge of a bog or pond and can winter outdoors. Consider creating a lined bog garden area so the nutrient levels can be kept low.

Propagation: Propagation is by division or leaf cuttings in spring, or by seeds, in warm humid conditions.

See the Pinguicula Grow Guide for more specific growing requirements.

Darlingtonia californica (cobra lily)

Cobra lilies have variegated pitchers at the end of the leaves. The pitchers are mottled green in colour and survive for two to three years. Flowers appear in spring before new pitchers and are greenish yellow or brick red. Seedheads last for a while and are good for drying.

Grow in pots stood in rain water, using equal parts by volume peat, washed sharp sand and perlite (or vermiculite), or outdoors in a cool, shady, boggy situation. Give winter protection outdoors, or move pots to a frost-free frame or greenhouse.

Propagation: The best method of propagation is by taking offshoots from the rhizomes.

Sarracenia (North American or trumpet pitcher), especially S. purpurea

A group of hardy to nearly hardy plants with pitcher-shaped leaves, sarracenias range in height from prostrate forms to those with pitchers 1m (3ft) tall. Pitcher colours vary from light yellow through green to purple. Flowers are formed from early spring to midsummer before the pitchers, some are scented and are suitable for cutting and drying.

In containers grow in equal parts in volume sphagnum moss peat and washed sharp sand with a little leafmould.

Propagation: Propagate by seeds in spring or from rhizome cuttings. Divide large clumps just before they come back into growth. Rooted crowns can be cut off and potted up in equal parts of moist coir and moss and kept moist at a temperature of 15°C (59°F).

Pruning and training: Remove any dead leaves or traps.

See the Sarracenia Grow Guide for more specific growing requirements.

Carnivorous plants for house and greenhouse

Most carnivorous plants will thrive in a bright position inside, but not in direct sun leaves can scorch through glass. Tropical species such as Nepenthes, however, prefer a shadier spot as they would grow in jungle conditions in their native habitat.

Nepenthes (monkey cups)

These are plants from the tropics, their natural range extending from Madagascar through tropical Asia to northern Australia. In the wild they grow as vines up to 15m (50ft). Their insect traps are pitchers formed at the ends of leaves mainly in summer and high humidity is essential for pitcher formation. Two types of pitcher are produced, one at ground level, the other further up the vine. Pitcher development is encouraged by pinching out new shoots at four to six leaves or by cutting back annually in spring to maintain bushiness.

Grow in hanging baskets of rot-resistant wood, using a loose porous richly organic medium, such as a mixture of rough fibrous peat, a little fibrous loam, sharp sand, sphagnum-type moss (if available), or bark fibre, and some charcoal.

Lowland species require very warm summer conditions with a winter temperature of 21°C (70°F). Highland species need frost-free winter conditions with a winter night temperature of not less than 11°C (52°F), but prefer a good level of warmth by day ideally 18-22°C (64-71°F). Both groups need shade and high humidity.

Propagation: The best method is by stem cuttings (in February) or by seeds sown in a finer version of the growing medium at 26-32°C (80–90°F). Shoots near the base of the plant root most readily.

See the Nepenthes Grow Guide for more specific growing requirements.

Cephalotus follicularis (Australian pitcher plant)

Cephalotus is the only member of the genus. It produces squat pitchers 6.5cm (2½in) high. Pitchers are pale green in normal light conditions and purple in bright sunshine. The traps appear in summer and plain, fleshy leaves form in spring. Flower spikes up to 60cm (2ft) in height are produced, although they are not spectacular.

It is a plant for warm greenhouse cultivation. Grow in equal parts by volume peat, washed sharp sand and perlite (or vermiculite). Position in direct light (if attempting indoors, on a south or west-facing windowsill) maintaining a winter night temperature not below 10°C (50°F).

Propagation: The best method of propagation is by root cuttings (during April/May), leaf cuttings or division.

Dionaea muscipula (Venus' fly trap)

Venus' fly trap is the only member of the genus. It is a greenhouse plant, native to eastern North America, with green leaves that bear traps at the ends at all times of the year except winter. The inner surface of the trap may be flushed pink or red if healthy. Each trap can be used two or three times for catching insects, before it dies naturally and is replaced. White, insignificant flowers are produced in spring.

Grow in frost-free greenhouse or windowsill in direct sunlight. Grow in two parts by volume peat to one of washed sharp sand. Alternatively, use two parts oak- or beechmould to one part washed sand. Always water by filling the saucer with rain water.

In winter, the plant will turn dormant and requires much less water. Temperatures of not lower than 10°C (50°F) are preferred but a greenhouse or frame temperatures maintained above freezing point (0°C/32°F) is acceptable.

Propagation: Venus’ fly trap can be propagated by seed. Sow thinly on the surface of moist, shredded sphagnum moss or perlite. Moisten the surface then stand the pan in a shallow tray or saucer of rainwater. Cover with glass or clear plastic – cling film is ideal – then place in warmth, ideally in the region of 21-26°C (70–80°F), ventilating regularly. Seedlings take several years to mature.

By leaf cuttings take these in early spring or early summer, using the entire leaf and leaf base, but having first removed the trap. Lay the cuttings flat on the surface of moist, finely chopped living sphagnum moss. Ensure the upper surface of the leaf stalk is facing upwards before covering with a fine layer of moss. Good humidity levels are needed and the use of a small propagator is advisable, ideally providing bottom heat of 21–24°C (70–75°F). Several young plants may develop. They can be left for 12 months or more before being potted up singly.

Dionaea can also be divided, but this is best delayed until the plant has made four or more crowns.

See the Dionaea Grow Guide for more specific growing requirements.

Drosera (sundew)

Sundews are a good choice to grow with other houseplants to protect them from small flies, making a very effective fly paper. They come from a number of areas of the world and each group has its range of species with specific requirements.

All sundews can be grown in a cold frost-free greenhouse but pygmies such as D. occidentalis prefer a winter minimum night temperature of not below 10°C (50°F).

Compost must be kept moist during the winter for all protected species. Some need a period of dormancy with dry conditions during the summer.

Propagation: Seed is the most successful method of propagating sundews. Leaf cuttings are also effective.

See the Sundew Grow Guide for more specific growing requirements.

Pinguicula (butterwort)

A north-facing windowsill suits most species. During the growing season, ensure there is always 2.5cm rainwater or distilled water in the plants’ saucer. In winter keep plants moist, however the Mexican species and hybrids (P. x wesser, P. laueana need to be much drier than other species over winter as they can rot whilst not in active growth.

Propagation: Leaf cuttings are the most reliable method of propagation. Mature plants can be divided by hand.

See the Pinguicula Grow Guide for more specific growing requirements.

Sarracenia (American or trumpet pitcher)

Indoors, grow in bright light, but in direct sun. Stand the containers of equal parts by volume of moss peat and washed sand in a tray of rain or distilled water. Maintain a high level of humidity in summer.

In winter, sarracenias need to have a period of dormancy, so several weeks spent in temperatures of between 0°C (32°F) and 15°C (60°F) will help encourage strong growth the following year. Reduce watering winter, but do not allow the plants to dry out.

Propagation: Propagate by seeds or from rhizome cuttings.

See the Sarracenia Grow Guide for more specific growing requirements.

Cultivar Selection

Dionaea muscipula (Venus fly trap): Can be grown on a windowsill in frost-free conditions.

Drosera aliciae: An easily grown rosette sundew suitable for a frost free conservatory or glasshouse.

Sarracenia flava: Yellow pitchers and flowers and is easy to grow in a frost-free position indoors.

Sarracenia × catesbaei: Yellow pitchers and red flowers. It thrives well indoors in frost-free conditions.

Sarracenia purpurea: A good choice for the bog garden being the hardiest sarracenia.

Links

RHS Find a Plant

Problems

Pests

Aphids can be a problem on carnivorous plants, but can be controlled with contact insecticides such as those based on plant and/or fish oils or fatty acids. These can be applied with a paint brush or sprayed. Mealybugs can also be a problem.

Diseases

Grey mould (botrytis) can occur. Remove any dead flowers or plant material as noticed.

Further reading

The Savage Garden by P D’Amato, Ten Speed Press (Berkeley 1998, ISBN 0-89815-915-6)

Carnivorous Plants by A. Slack (Marston House  2000, ISBN 1-899296-13-1)

The books are also made available through the RHS Lindley Library.

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