The many species and varieties of tropical bamboos come in many sizes, overall forms, leaf sizes, and textures - solid green & variegated. Most have green culms (canes) - some have striated culms (vertical stripes). Some species have a powder (bloom) or a furry coating on their base-green culms which changes the appearance to a spectacular light blue, silver, white, or tan/brown color. A few species have culms that mature to a jet black or chocolate brown. One of these species’ culms become glossy black, another becomes matt black, and a third has massive culms that transition from furry tan to chocolate to matt black from the bottom to the top. Finally, there are a group of bamboos with yellow or gold culms. They all have varying striations of green on their culms but the dominant color is a shade of yellow.
Each of these culm colors, or color combinations, will be affected by the sun. Intense, direct exposure will cause sun scalding while even moderate exposure will change the original color over time. If the culm is originally green, it will lighten to a pea green or even an orange/yellow. The species with powder or fur-coated culms are initially self-protected but the powder or fur eventually wears off. The culms will then lighten like any green culm. Black bamboo species all develop silver/white areas on their culms. Silver spots, streaks, or just an entire area of silver can replace the black on the culm. Yellow culms change to light brown or often develop dark brown spots or blotches. These color changes often are obvious on one side of culms in an entire clump (the south side) as the Florida sun most often angles from the southern sky.
What can be done to prevent culm discoloration? Well, first, it’s a natural process and it’s not unhealthy for your bamboo. Since you’re most likely growing it as an ornamental plant, there are ways to manage culm appearance.
Remember that most tropical bamboos love sunlight on their leaves. The growth rate is proportionate to the energy, water, and fertilizer they receive. In their natural growing environment, they are permaculture plants and grow among many other tropical plants. Usually, at least their bottom half is protected from the sun and shaded by the surrounding flora. If you can simulate this in your garden with plants or structures, the bamboo culms will stay beautiful for much longer (just make sure your bamboo continues to get sunlight at the top).
Creating a private jungle is not always practical. You’ll most likely have to just manage your bamboo by pruning out the culms as they age and discolor. Don’t get too carried away – never remove more than 1/3 of the total mass in a calendar year. You should easily have enough new shoots each year to replace most of the unattractive, oldest culms. Just cut the offending culms at ground level (leave no stump) and dispose of them or use them for crafts (the cut culms of some species may be used for propagation). If you remove lower branches to better reveal the beautiful culms, remember that you're also allowing more sunlight to strike the culms. Be judicious when you reduce the bamboo's natural "umbrella".
Sometimes an ugly culm or culms must be left in a clump because they would leave a gaping hole if removed or maybe too many have been removed already. On a black bamboo in the display gardens at Tropical Bamboo Nursery & Gardens, we have actually used black shoe polish to erase a silver area on a culm. At first this may seem funny but it’s turned out to be a fine short-term solution. The prospect of having to look at an ugly culm for several months until the new ones developed to replace it was solved by sponge-on shoe polish. I know of one person who has artistically used paint on her live bamboo (with no detrimental effect on the bamboo).
The appearance of your bamboo will always be in flux as it’s such a fast-growing plant. If at some point you’re not pleased with a culm or group of culms, you can take solace that they will soon be replaced and the clump will transition to a fresh new look.
Tropical Bamboo Nursery & Gardens