Why Dieffenbachias Get Brown and Yellow leaves

Hi Judy,
This plant is at my office. It sits on my desk under fluorescent light with a very high ceiling. It is also about 4 feet away from a window that faces southeast and gets lots of light. The plant was a vibrant green when I got it. Now it is faded and the leaves are yellowing and turning brown in spots. I only water it when the leaves just begin to droop.
Thanks, Susan

Hi Susan,

Your plant is called a Dieffenbachia. The edges of the leaves of a Dieffenbachia plant usually turn brown from too much plant food or too much salt, fluorine, or chlorine in your water. Never use water that has passed through a water softener; it is too salty. Rinse the soil with distilled water to get rid of any unwanted chemicals and salts. If the water in your office has a lot of chemicals it, allow it to sit out over night before using it or use distilled water. Dieffenbachia should be fed every two weeks in the summer and once a month in the spring and fall. Never feed a Dieffenbachia in the winter. Dilute you fertilizerPlants need fertilizer only when they are actively growing. Slow growing plants in low light require very little plant food. Too much fertilizer is worse than not enough. Most plants prefer a water soluble plant food at 1/2 the recommended strength. Plants that are in bloom or dormant should not be fertilized. Houseplant food contains nitrogen (N), phosphorus (P), and potassium (K). A fertilizer containing these elements in equal proportion is considered a balanced plant food. Nitrogen helps in photosynthesis and encourages the growth of leaves and stems. Potassium and phosphorus also help in photosynthesis and aid in root and flower development. Most fertilizers have trace elements of other minerals that are lacking in the soil but are necessary for good plant growth. Fertilizers have a high salt content. If a plant is not producing new leaves and doesn’t absorb the fertilizer, salts build up in the soil. These salts can burn the roots, discolor the leaves, and cause new growth to be small. to 1/2 the recommended strength. Excess plant food quickly causes browning around the edges of the leaves.

You might want to move your plant to an area that gets less light. Your dieffenbachia may be getting more light than you think and this could be causing the fading color. Check the backs of the leaves and see if they feel gritty. This would indicate a spider miteSpider Mites, members of the Acari family, are small insects about 1mm in size. The most common indoor plant mite is the red spider mite (also called the two-spotted spider mite.). These pests lay their eggs on the under surface of leaves and produce fine webbing especially where the leaves are attached to the stem. Spider mites are hard to see with the naked eye, and may appear only as small red dots. They are more often recognized by the gritty feel of the leaf when you run your finger down it’s length, or by the appearance of discolored leaves due to the sucking action of the mites. The best way to prevent spider mites is to keep your plants clean and dust free. Treat spider mites by spraying every ten days for a month with a product such as Safer Insecticidal Soap. problem. The mites suck the color from the leaves.

All parts of a Dieffenbachia are extremely poisonous which is how they earned the nickname “dumb cane plant”and should be kept away from pets and children. Read more about common houseplants that are poisonous in Don’t Feed Me To Your Cat! A Guide to Poisonous Houseplants