Does your bamboo have yellow leaves? Is this a concern? It depends. Below I'll list several different conditions where yellow leaves happen and what to do about it if anything. Remember, bamboo is a tough plant, but it is possible to kill, and 99% of the time people accidentally kill their bamboo, it is due to either over-watering or under-watering or a combination of those things. Everyone wants to know how often they should water, but there is no set answer for this. It depends on the weather, the soil, the type of bamboo, and the time of the year. The only sure-fire way to know if your bamboo is getting the proper amount of water is to check the soil at the root ball several inches down if possible. It should be moist but not soggy. Remember: bamboo typically likes a moderate amount of water: not too much and not too little. So my advice whenever someone has a concern about their plant is to check the root ball. It would be best if you did this regularly until you feel you have an idea of what the bamboo needs and/or until the plant is established. Most plantings in the ground can take care of themselves after 6~24 months, depending on the size of the plants you started with. For bamboo in containers, you'll always need to make sure they have water since a container cannot store water like the ground.
Less than 20% yellow leaves at any time of year: normal
When a bamboo leaf turns yellow, it means that it is dying, and for most types of bamboo will soon fall off the plant. Like all evergreens, bamboo will lose leaves throughout the year, and thus you'll always have at least a few yellow leaves. Bamboo leaves typically last about a year. Look for an even distribution of the yellow leaves throughout the whole plant.
Up to 50% of yellow leaves in spring and fall: normal for some types
Some bamboo types will drop more leaves than usual two times per year: once in the spring when the weather turns from cold to warm, and once in the fall when it does the opposite. These are essentially stress responses from the plant due to the change of conditions. If you notice bamboo having more yellow leaves during this time of the year, check the soil at the root ball to make sure there is enough moisture but not too much.
Localized yellow leaves or lots of yellow leaves: could be not normal
If you have many yellow leaves in one place or all over, this isn't normal. This could be due to several reasons:
1 - Overwatering. This is the most dangerous condition and needs to be remedied immediately. If you check the ground around the root ball and determine it is in fact too wet, the water needs to be reduced as quickly as possible. If it is too wet due to either automatic or manual irrigation, stop all irrigation until the situation returns to normal conditions and then adjust watering times and durations to fix the problem. If there is mulch, then that can be removed to help it dry out quicker. If the bamboo has too much water due to excessive rain, see if you can drain the excess with a ditch and redirect future excessive water with diversion techniques: usually either a berm or trench. If the bamboo has been recently planted, you may need to dig it up and re-plant it higher.
2 - Nutrient deficiency - Sometimes, bamboo can be short on a nutrient or combination of nutrients that may make its leave yellow. If the leaves are yellow but not falling off, this is often the case and gradually happens. Iron is the most common deficiency and can be fixed with a product like Ironite, which is cheap and readily available at almost any garden supply, including Lowe's and the Home Depot.
3 - Sun bleaching - some bamboo leaves and culms and branches can get bleached out from green to yellow due to sun exposure. This is normal.