My Black Bamboo is growing extremely well, very tall and quite dense - I think it needs thinning. Which stalks should I take out ? Old / New? Thick / Thin? Black / Brownish / Green?
I would always take the weaker growth out first and then see where you are with it. It should open it up enough for you to see where any other culms can be removed. The culms come up green and turn black when they age and you shouldn't remove all the new growth.
I would remove all canes that are thin, spindly, discoloured, damaged or diseased, leaving the wider, taller, stronger canes. Then you can think about further pruning if necessary. I have just done quite a drastic pruning of some of my bamboo. I like to see the colour of the canes so I also remove the bottom third/half of the leaves on each cane. Letting more light in gives the canes a more sculptured look and improves airflow, avoiding possible fungal infection. I removed about 20 canes from this clump - they were hitting the guttering and shading the plants below:
I sometimes wait a bit after the first pruning to observe how the clump opens up. This was the second pruning for the clump above. It's best to cut the canes as closely to the ground as possible and work methodically from side to side, trying to give each remaining cane equal space between them.
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Thin to open up the plant, especially those stems with a lot of branching. Thick as they are useful to have around.
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The culms come up green and turn black when they age and you shouldn't remove all the new growth.
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