Why Dieffenbachias Get Brown and Yellow leaves
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.
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 fertilizer 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 mite 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.