Answer: The most common reason to see foliage problems with bamboo indoors is probably lack of humidity. This is especially true when running the heating system during the winter and sometimes true when the air conditioning dries out the air in summer as well. To increase humidity, try placing the pot on a pebble tray to humidify the air. This is a shallow tray filled with pebbles and water. Place the pot on the pebbles and add water to just below the bottom of the pot. Top up as needed to maintain the steady evaporation process. Also, make sure the plant is protected from both hot and cool drafts.
Watering can cause problems, most bamboos slow their growth in the winter in reaction to the reduced light and then grow faster again in the spring and summer. When in a slowdown period, they need slightly less water than they need in a growth spurt. When growing, they need an evenly moist soil but not a sopping wet condition. When you water make sure the water is soaking down into the soil and not running out between the soil and the side of the pot. Check the soil surface down about an inch or two and see if you need to water or not. In a large pot, the bottom of the soil can still be wet while the surface is dry; sometimes the heft of the pot can help you know if you need to water or not. Your goal is not to overwater or underwater. If it has grown a lot, and is too big for the soil mass and thus drying it out quickly, it may need to be repotted.
Another possibility is that the plant has spider mites or another insect problem. Look for stippling of the foliage, and also look for fine webbing on the underside of the leaves and/or along the stems. These can be washed off with water and treated with insecticidal soap according to the label instructions. Increased humidity will also help control them.
Yet another possibility is that the plant is in too much direct sunlight now that the days are growing longer and brighter. Some bamboos prefer ample light, some prefer more moderate but still bright light and others do better with less light. This would depend on the variety and you might experiment with gradual changes (moving the plant back a bit, adding a sheer curtain, changing the exposure) if you suspect this is the problem.
Finally, what you are seeing may be natural. In spring, bamboos will lose some older foliage which is then replaced/balanced by the new incoming growth. Perhaps you will be able see if this seems to be the pattern.
I hope this helps you troubleshoot.
Q&A Library Searching Tips