Dieffenbachia amoena -- also known as dumb cane -- is a tropical broadleaf evergreen plant growing in U.S. Department of Agriculture plant hardiness zones 10 and 11. Grown mainly for their attractive foliage, these exotic evergreens are used as a houseplant in areas where not hardy. Dumb cane is simple to care for; however, problems can occur if the basic needs of this plant are not met. All parts of the plant are toxic and can cause skin rash or death if ingested. Wear gloves when handling the plant and situate it in an area of the home or landscape away from children and pets.
According to the Clemson Cooperative Extension website, mealybugs and aphids are the main insect problems plaguing the dumb cane plant. Both mealybugs and aphids measure about 1/8 inch in size and feed on the cell content of plants. Thankfully, these insects rarely threaten the life of the dumb cane plant and can be easily controlled. Some common houseplant pests can be controlled by simply hosing the dumb cane plant off with a water hose. The blast of water will wash spider mites and aphids off the plant without the use of chemicals. You may need to repeat this action once every few days until the infestation is controlled. Mealybugs will require manually wiping the pest off the plant with a cloth dipped in rubbing alcohol. Another option is to spray the foliage of the infested plant every seven to 14 days with ready-to-use neem oil to control mealybugs and aphids.
When grown as a houseplant, an extremely common disease problem is root rot, which is caused by excessive watering and poor soil drainage. Yellowing of the lower leaves and rotting at the base of the plant are symptoms of root rot. Growing the dumb cane plant in the proper medium and providing adequate irrigation will ensure the plant doesn’t develop root rot. A fertile, loose, highly organic growing medium will be able to hold water while still providing proper drainage. When watering the dumb cane, water deeply and regularly but allow the surface of the soil to dry between waterings.
Cultural problems -- such as too much or too little heat -- can quickly take their toll on the dumb cane plant. For example, excessive heat will cause leaves to dry up, resulting in browning at the leaf tip and edge. Grouping plants together or growing the dumb cane on a pebble tray will help maintain proper humidity and keep the foliage from drying. Furthermore, position the plant away from radiators, heaters and fireplaces to help prevent problems that will affect the dumb cane plant. If possible, try to prevent sudden fluctuations in temperatures in the room where the plant is growing and keep it away from drafts. These sudden temperature changes will cause the lower leaves to drop. For optimal growth, keep the room between 65 to 75 degrees Fahrenheit.
Care and Maintenance
Improper care and maintenance -- such as inappropriate placement and improper fertilization -- is a common cause of problems for houseplants of all species. Direct sunlight will cause the colors of the dumb cane to fade, and too little light leaves the plant long and spindly, trying to “reach out” for a light source. Furthermore, low-light situations will result in the bottom leaves falling off the plant. Dumb cane plants grow best when placed in an area with indirect bright light. Another cause of problems is an excessive amount of fertilizer, which will cause burning at the leaf margins. However, if the dumb cane is lacking vital nutrients, the plant will experience yellowing leaves and stunted growth. Since the amount of fertilizer given to the dumb cane plant varies from one situation to the next, the University of Connecticut Home & Garden Education Center website suggests applying a 20-20-20 fertilizer every four to six weeks during the plant’s active growing season.