Dionaea

Species pages start from this and record only where they differ.

Light

Full sun — as much as you can give it. Indoors NC State quantifies the target as 15,000-25,000 lux for around fourteen hours a day, which is a grow light rather than a windowsill. This is not a bright-indirect plant and it is not a terrarium plant: it wants sun and moving air.

Water

Rainwater, distilled or reverse osmosis. Tap water only if you have measured it below 90 ppm total dissolved solids — and filtering does not remove dissolved salts. Stand the pot permanently in a tray of pure water, with the water more than 5 cm below the soil surface. The failure mode is slow and diagnostic: minerals accumulate until new leaves come up as bare petioles with traps that do not work.

Humidity

Not the issue people think it is. No carnivorous-plant authority publishes a figure, and an enclosed, still, humid case is a worse bet than an open sunny windowsill — Botrytis turns up in enclosed spaces, and the treatment is more air movement and more light.

Temperature

Happy from around 70-95 °F (21-35 °C) in summer. For the winter rest, 35-50 °F (2-10 °C). It is frost-hardy in its own range and does not need protecting from a light freeze once genuinely dormant.

Substrate

Nutrient-poor and deliberately starved: pure sphagnum, pure sphagnum peat, or the standard 1:1 peat and sharp sand. No compost, no added feed, no lime. ICPS advises against perlite and vermiculite as potentially salty, though several growers use perlite without trouble. Peat-free mixes work — the RHS has been trialling them on this species since 2023.

Fertilizer

None in the soil, ever. ICPS puts it as plainly as it can be put: do not fertilise unless you do not mind killing the plant. Nutrition comes through the traps, and that is real physiology rather than theatre — prey triggers the genes for both the digestive enzymes and the nutrient transporters. Feed dried bloodworms or an insect if you feed at all; an established plant outdoors catches its own.

Propagation

Division of the rhizome, leaf pullings taken with the white base intact, or seed — which is slow, several years to a mature plant. Flower stalks cost the plant a lot; cut them off unless you want seed.

Dormancy

The one thing to get right, and it is not as simple as it is usually told. The trigger is photoperiod, not temperature. A plant on a windowsill gets the short-day signal in autumn whatever the room temperature, starts shutting down, and then burns through reserves it cannot replace if kept warm — which is the slow decline over two or three seasons that growers describe. So for a windowsill plant a genuine cold rest is required: at least ten weeks, ideally three or four months, at 35-50 °F (2-10 °C). The exception is real and worth knowing: a plant kept under strong light for fourteen hours a day all winter never gets the signal, and ICPS says outright that such a plant does not need dormancy and that putting it in a fridge is a waste.

Common problems

• New leaves emerging as bare petioles with small or non-functional traps is the classic mineral-burn signature — the water is the cause, not the light
• A trap that has closed stays out of service for a day or so and then reopens. Triggering them for fun wastes the plant's energy; the often-repeated claim that a trap dies after three or four closures is not something I could find in any authority
• Feeding it meat is genuinely harmful — too much protein and energy for what the trap can process, and the trap usually rots
• Black, mushy traps in still humid air are usually Botrytis. Treat with more light and more air movement, not less
• A plant that fails to wake in spring after a warm winter indoors has usually been dormant without the cold, and exhausted itself
• Flower stalks in spring are expensive. Cut them unless you want seed

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In the collection