Why Are Your Bamboo (or Pine Trees) Turning Yellow in the Fall?
Why are my bamboo's leaves turning yellow in the fall?Bamboo plants are evergreen, which means they keep their leaves throughout the entire year. Coupled with their fast growth and beautiful habit this is what makes bamboo so popular for privacy hedges and screens, but being evergreen doesn't mean they keep the same leaves forever. As leaves age they become less efficient and they also tend to be outcompeted for light as new leaves and stems develop higher up the plant, so plants shed their oldest leaves throughout the year. At any point during the growing season you can find a few yellowing leaves here and there but suddenly in October and November there are so many that the plant starts to look yellow as a whole.
There are so many yellow leaves in the fall because a high proportion of the total leaves are roughly the same age and turning yellow together - these are the leaves that emerged following high amounts of new growth in the spring. As these leaves all age together they start to yellow and drop together in the fall. Many other evergreen species have similar cycles with pines, firs, and hemlocks dropping up to a third of their needles around October while showing the same yellowing patterns. Evergreen plants can drop their leaves in other times of the year instead, such as the Pacific Madrone which drops up to half of its leaves in June and July.
Does this leaf drop make my bamboo plants less dense?Although having many leaves drop off your bamboo at once does leave your grove slightly less dense, most species of bamboo are actually busy growing new leaves at the same time so there usually isn't a noticeable difference. This is not true for many other evergreen species, especially pines, where new leaves do not emerge until the following spring - leaving the plant noticeably thinner than before.
How do I tell if the yellowing leaves is normal or a sign of poor health?You can easily determine whether yellowing leaves on your bamboo plants is normal of a symptom of a problem by looking at which leaves are yellow. A healthy plant will drop about one third of its total leaves, potentially up to half, but the leaves that drop are on the base of each leaf clump. On bamboo plants you will see that the leaves are arranged in clumps around an individual twig - usually with five to eight leaves per twig. The leaves closest to the tip of the twig are the youngest and they should remain green while the leaves at the back will turn yellow and drop off. If you see a lot of yellow leaves on the tips of branches or most or all of the leaves are turning yellow then that might be a sign of poor health.
If most of the leaves are yellow, what do I do?If most of the leaves are yellow then there can be several causes. Poor soil conditions generally cause poor root development which makes it difficult for plants to absorb the proper nutrients. This can be fixed by applying a thick mulch in the fall or spring and fertilizing with a slow release pellet like Osmocote in April.
Poor watering will also leave a plant in overall poor health with yellow leaves. Too little water or frequently drying out over the summer leads to disrupted cellular processes which can yellow the leaves. Be sure the plant is well watered from here on out if this is the case. Remember: most bamboo species will curl their leaves when they are dehydrated so if you see this during the growing season water your plants more. Overwatering your plants can have the same effect of yellowing leaves, if the soil has been consistently soggy over the summer this is probably the case. Try to water your plants for long periods of time but less frequently for optimum root growth, we water plants in the ground for two hours twice a week with a good soaking sprinkler throughout the summer and this tends to get the best results (we are in a very arid, low-humidity environment where summers are often over 100 degrees, watering less often may be necessary in wetter/cooler/humid environments).
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