Dieffenbachia

Light and exposure

Dieffenbachia wants bright but indirect light, never direct sun. Behind a south-facing pane during the hot hours, its large leaves scorch and develop bleached patches. The ideal is a bright room, one or two metres from an east or west window, or behind a sheer curtain.

Beware the opposite excess: in a corner that is too dark, the lovely cream variegation fades, the leaves turn green again and the stems stretch towards the light, becoming spindly. In Belgium, where winter light is weak, move it closer to the window from October to March and turn the pot a quarter turn each week to keep the plant upright and even.

Watering

Dieffenbachia likes a substrate that stays fresh, without ever sitting in water. Water as soon as the first one or two centimetres of the potting mix are dry to the touch, soaking the root ball thoroughly, then empty the saucer. Water standing at the bottom of the pot rots the roots, which is the leading cause of losing this plant.

In winter, cut back sharply: growth slows and the substrate dries more slowly, so watering every ten to fifteen days is often enough. Preferably use water at room temperature, as cold water straight from the tap shocks the tropical roots. Leaves that yellow and soften almost always signal too much water, not too little.

Soil and repotting

A potting mix for green plants, rich and light, loosened with a handful of perlite or bark, suits it well. The mix should hold moisture while letting water pass through. A pot with a drainage hole at the bottom is essential, with a layer of clay pebbles to keep the roots from sitting in water.

Repot in spring, roughly every two years, or when the roots come out through the drainage holes. Move up to a barely larger pot, as too vast a container holds too much water. Take the chance to renew the top layer of potting mix each year. Put your gloves on for this operation: breaking the roots or a stem releases the irritant sap.

Temperature and humidity

Dieffenbachia is a warm-climate plant. It thrives between 18 and 24 degrees all year and does not like to drop below 15 degrees. Below 10 degrees it suffers quickly, the leaves browning and dropping. Keep it away from draughts, slamming doors and cold windows in winter.

Air humidity is its real Achilles heel here. It comes from a humid environment and hates air dried out by central heating: the leaf edges brown and dry out as soon as the atmosphere becomes too dry. Mist the foliage several times a week in winter, set the pot on a bed of damp clay pebbles, or group your plants together to create a more humid microclimate.

Pruning and upkeep

Routine care is light. Remove yellow or damaged leaves at the base as they appear, with clean secateurs and gloves. Regularly wipe the top of the large leaves with a damp cloth: dust dulls the variegation and clogs the plant’s breathing.

Over time, dieffenbachia goes bare at the bottom and takes on a cane-like habit, a naked stem topped with leaves. You can then cut the stem back hard to fifteen or twenty centimetres in spring: it will regrow from the base. Do not throw away the cut sections, as they serve to propagate the plant. A useful reminder with every cut: the sap is toxic and irritant, gloves are mandatory and hands washed afterwards.

Pests and diseases

The real trouble comes mainly from too much water. A waterlogged substrate rots the roots and the collar: the plant softens, the stems turning soft and brown at the base. The answer is prevention, a drained pot and measured watering. Brown spots on the leaves can also appear in cold, damp weather combined with wet foliage.

As for pests, the dry air of the heating favours spider mites, tiny mites that spin fine webs and speckle the underside of the leaves with yellow dots. Mealybugs, whether floury or armoured, also settle in the leaf axils as white cottony clusters or small brown shells. Inspect the underside of the leaves each week in winter, raise the air humidity against spider mites, and clean off mealybugs with a cotton swab soaked in methylated spirits.

Propagation

Propagation is done in spring, on the occasion of a repotting or a pruning. The simplest method is cutting from stem sections: cut the bare stem into segments of five to eight centimetres, each bearing at least one node, let the sections dry for a day, then lay them half-buried in a light, moist potting mix, kept warm between 22 and 25 degrees. New shoots emerge from the nodes within a few weeks.

For a specimen that has grown too tall and bare, air layering gives excellent results: notch the stem below the crown of leaves, wrap the wound in a ball of damp moss held with plastic film, and wait for roots to form in the moss before cutting below the roots and repotting the head. Wear gloves for all these operations, as each cut releases the irritant sap.

Toxicity

A plant that is very toxic through all its sap. The tissues contain calcium oxalate crystals (raphides) that lodge in the mucous membranes the moment a piece of leaf is chewed: intense and immediate pain, burning, salivation, swelling of the mouth, tongue and throat, and sometimes a temporary loss of voice. It is this loss of voice that earned it the name dumb cane. Dangerous for children, cats and dogs, who may nibble at it out of curiosity. Mere contact with the sap also irritates the skin and eyes. Place it out of reach, wear gloves to prune or repot it, and wash your hands after handling.

Month-by-month care calendar

Green Hub tips

• Toxic sap: keep the dieffenbachia out of reach of children, cats and dogs, and always put on gloves to prune or repot it.
• Leaf edges browning in winter? It is the heating drying the air. Move it away from radiators and mist, or set the pot on damp clay pebbles.
• Variegation that pales and stems that stretch signal a lack of light. Move closer to the window, especially from December to February.
• Yellow, soft leaves: nine times out of ten it is too much water. Let the top of the potting mix dry between waterings and empty the saucer.