Dumb cane

Dumb cane: how do you recognise it?

Habit

An upright plant with one or a few thick green stems, 1–1.2 m tall indoors and about 60 cm across.

Leaves

Large, oval to oblong, 20–40 cm long, glossy green with cream, white or pale green spots or markings.

Stem

Thick, fleshy and marked with scars from old leaves; the lower leaves drop over the years, leaving the stem bare.

Flowers

It rarely flowers indoors. The flower is a greenish spadix surrounded by a spathe, typical of the arum family.

Sap

Contains needle-shaped calcium oxalate crystals that irritate the mouth, throat, eyes and skin on contact.

Plants: March–May · Pruning: March–April

Why grow it?

• Large, decorative leaves that look good all year.
• Grows fast and quickly brings a tropical touch to a room.
• Tolerates a spot out of direct sun, so it can stand some way back from the window.
• Easy to propagate: one old plant gives several new ones from stem cuttings.
• There are many varieties with different markings, from almost all green to almost all cream.

Dumb cane: where does it grow best?

• Bright light to partial shade, out of direct midday sun: strong sun scorches the leaves, too little light makes the markings fade.
• Warm: 18–25 °C is ideal, never below 15 °C. No draughts and not next to a cold window.
• Fairly high humidity; do not stand it right above a radiator.
• Choose a spot out of reach of children and pets.
• Give the pot a quarter turn now and then so it grows straight.

Light

Bright, out of direct sun

Potting soil

Multi-purpose compost or airy, humus-rich compost

Acidity

Acid or neutral

Watering

Moderately

Size

1.2 m tall, 0.6 m wide

Temperature

Minimum 15 °C

Goes well with

• Swiss cheese plant: Another large-leaved member of the arum family, for the same bright spot out of direct sun.
• Peace lily: White spathes and dark green leaves; it likes the same warmth and humid air.
• Boston fern: Fine, airy fronds beside the large leaves; grouped together, the plants keep the air more humid.
• Calathea: Striped and patterned leaves that also need warmth and humid air.

Dumb cane: when and how to plant it?

Plant in March–May.

1. Repot in March–May, every 1–2 years, when the roots fill the pot.
2. Choose a pot 2–4 cm wider than the old one, with a drainage hole.
3. Use an airy houseplant compost mixed with some perlite or fine bark for good drainage.
4. Set the plant at the same depth as before, fill in and firm lightly.
5. Water until it runs out of the bottom and empty the saucer after a quarter of an hour.
6. Wear gloves when repotting: the sap irritates the skin.

Care

Watering

Water when the top 2–3 cm of compost feels dry. Never leave water standing in the saucer. Water less in winter.

Humidity

Stand the pot on a tray of pebbles and water, or group it with other plants. Wipe the dust off the leaves with a damp cloth.

Feeding

From April to September, houseplant feed at half strength every 2 weeks. None in winter.

Repotting

Every 1–2 years in spring, into a slightly larger pot.

Old leaves

A few yellowing lower leaves are normal on an older plant; cut them off close to the stem.

Tip: If it goes bare at the base, cut the stem back to 10–15 cm in spring: the stump sprouts again, and the top and stem sections give you new plants. Always wear gloves when you do this.

Dumb cane: when to prune it?

Pruning months: March–April.

When: In March–April, when the plant gets too tall or bare at the base. Otherwise no pruning is needed.

How:

• Cut the stem with a clean, sharp knife to 10–15 cm above the compost; new shoots grow from the stump.
• Use the cut top and the pieces of stem as cuttings.
• Cut yellow or damaged leaves off at the base of the leaf stalk.
• Wash your hands and the knife thoroughly after pruning.

Caution: Always wear gloves and do not touch your eyes: the sap strongly irritates skin, eyes and mouth.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Tip cuttings

From April to August, cut off the top with a few leaves, let the cut surface dry briefly and stand it in water or moist cutting compost at 20–25 °C. Roots form within a few weeks.

Stem sections

Cut a bare stem into 5–8 cm sections, each with at least one bud. Lay them half buried in moist compost, bud facing up, and keep them warm under plastic. They start to grow after a few weeks.

Dumb cane: how does it get through the winter?

• Indoors all year: it cannot take frost and already suffers below 15 °C.
• In winter, water less and do not feed; let the top layer dry out well.
• Stand it in the brightest spot out of direct sun, away from cold windows, draughts and hot radiators.
• Against dry air from the heating, raise the humidity with a tray of water and pebbles.

Diseases and pests

• Spider mites: Fine webbing and pale speckles on the leaves, especially in dry air. Rinse the plant in the shower and raise the humidity.
• Mealybugs: White, woolly tufts in the leaf axils. Remove them with a cotton bud dipped in a little alcohol.
• Stem rot: Soft, brown patches at the base of the stem, from too much water or cold. Water less; if the rot is severe, root the healthy top as a cutting.
• Brown leaf tips: Caused by dry air or irregular watering. Water more regularly and raise the humidity.
• Yellow leaves: A few lower leaves: normal. Many yellow leaves: too much water or too cold.

Through the year

• January: Little water, no feed. Brightest spot out of direct sun.
• March: Repot, or prune if it is getting too tall.
• April: Repot or prune. Feed every 2 weeks again. Take tip cuttings.
• May: Repot. Feed. Take cuttings.
• June: Feed. Protect from strong midday sun.
• July: Feed. Water regularly and dust the leaves.
• August: Feed. Watch for spider mites in hot weather.
• September: Last feed of the year.
• October: Water less. Move it away from cold windows.
• December: Little water. Raise the humidity against the dry air from the heating.

Edible and useful

Not edible. All parts of dieffenbachia are poisonous, especially the sap of the stem and leaves: it is full of needle-shaped crystals (calcium oxalate) which, when chewed, cause intense burning pain and swelling of the lips, tongue and throat, so that speaking and swallowing become difficult, hence its name, dumb cane. Sap in the eyes causes pain and inflammation: rinse at once for a long time with lukewarm water and see a doctor. Children, and cats and dogs that bite the thick stem or the leaves, are most at risk: keep it out of their reach. Wear gloves, and preferably glasses, when pruning, taking cuttings and repotting, and wash your hands and your knife afterwards. Call your vet if your cat or dog has eaten some. If any is swallowed, call a poison centre (in Belgium 070 245 245) or your doctor at once.

Did you know?

• The name dumb cane comes from the effect of the sap: anyone who chews a piece of stem gets a swollen mouth and may find it hard to speak for a while.
• The genus is named after Joseph Dieffenbach, a head gardener in Vienna in the 19th century.
• It belongs to the arum family, like the Swiss cheese plant and the peace lily: its rare flower is a spadix surrounded by a spathe.