A popular indoor foliage plant, dumbcane (dieffenbachia) derives its common name from its sap, which contains calcium oxalate crystals that irritate the mucous membranes of humans and animals. When chewed, the leaves cause the tongue and throat to swell, making it impossible to speak. The plant reaches up to 6 feet in height with a spread of up to 3 feet, though modern hybrids typically grow in a more compact habit. Valued for their eye-catching, tropical foliage and ease of care, dumbcane plants produce large leaves marked with spots, stripes or colored veins, depending on the variety.
Site and Soil
Although tolerant of many growing conditions, dumbcane performs best when provided with bright, indirect light, such as that from an east-facing window, throughout the spring, summer and fall. During winter, the plant needs bright light or full sun for the best results. Dumbcane tolerates low light intensity, but this typically causes slower growth. Turning the plant about once per week ensures it grows evenly and receives enough light. A high-quality container soil mix with good drainage and a container with drainage holes in the bottom provides the best growing medium for the plant.
Dumbcane enjoys normal household temperatures and cannot tolerate extreme hot or cold. Temperatures constantly above 55 degrees F prevent cold damage. Temperatures of 60 to 75 degrees F during the day and 60 to 65 degrees F during the night provide the ideal growing conditions for the plant. Protecting against cold drafts and major temperature changes prevents the plant from yellowing or dropping leaves. Keep away from drafty windows and doors during the winter to keep the plant healthy.
The dumbcane plant requires watering whenever the top 1 inch of soil becomes dry to the touch. To check if the plant needs water, stick your finger into the soil to the first knuckle. If the soil is dry, it's time to water, but if the soil is moist, check again the next. In most cases, watering about once a week will provide the plant with adequate moisture. Water thoroughly at each application until water begins to drain from the bottom of the container. Draining off any excess prevents rotting, which can become a problem with consistently waterlogged soil.
Feeding once every two to four weeks during spring through fall provides dumbcane with enough nutrients to continue producing large, attractive leaves. Using a liquid houseplant fertilizer formulated for foliage plants further enhances growth. Alternatively, a time-released fertilizer, used according to the manufacturer's instructions, provides adequate nutrition and requires fewer applications. For best results, apply the fertilizer at half the recommended strength, as too much fertilizer may cause the plant's delicate leaves to burn.
Pruning and Re-Potting
As the plant matures, it naturally drops its lower leaves to reveal trunk-like stems. If these stems become long and bare, dumbcane is rejuvenated by cutting them back to about 6 inches in height. New growth appears below the cut shortly after. Removing damaged or diseased leaves whenever necessary increases health and visual appeal, and aside from this, the plant requires no other supplemental pruning. Re-potting when the plant becomes too crowded in its container keeps dumbcane happy. Re-pot in early spring before new growth begins using fresh soil and a slightly larger container for the best results.