Spindly Bamboo

I have bamboo (Phyllostachys Nigra), which is growing well (very healthy green lea ves) but its stems are very spindly so when it rains, it ends up laying prostrate on the border and onto the lawn. Ive ended up staking it to keep it upright. If I dont stake it, it just flops again. Why is it so spindly? Its in good light, which isnt full blazing sun all day, but does get direct sun on it for up to 3/4 hours a day (when sunny!). I water it well, and when I planted it (two years ago), I planted it in good soil with good supply of well rotted manure. Havent fed it since. Do stems thicken up over time?

I've heard this variety is particularly prone to spindly stems. I'm not an expert on bamboo and I'm sure someone else will give better advice shortly, but apparently you should cut out any particularly weak and spindly stems as soon as they emerge, leaving the stronger ones to use the energy to get thicker. That's not to say I would recommend chopping loads of it down wholesale now though, it might shock the plant. Perhaps you could thin out a third of the weakest stems and keep on top of any new spindly growth. Then next year, if the plant seems healthy and some stems are thickening, you might cut out a little more of the weak stems, and so on. I hope that makes sense. I also hope someone more knowledgeable comes along and says whether this advice is good!

I think Bronnie makes a good suggestion about thinning the weakest stems of the plant. We had a well established Phyllostachys Nigra plant that had to be moved due to building work, when it was replanted in its permanent home it sulked for a whole season, at least, and threw up some very pathetic canes. I made sure it had as close to ideal conditions as possible (as you have done) and pruned out the most spindly stems as the emerged and kept any slighty thicker ones. This summer (3 years later) it has had its best year yet and I have gone back to stripping the leaves off the lower half of the canes to reveal the black stems. I think you may have to be very patient - maybe they don't like being transplanted?!

The black one does tend towards the whippy... As already suggested, chop out some of them (I'd start with the ones that flop and annoy you the most), then chop some more when any new shoots appear next year. Feed it at the same time, mulch with manure as well, chuck any clay you might dig out from elsewhere onto it for the worms to slowly take down and water water water when its in growth. Once it begins making thick stems, it should continue to do so with minimal input from you, but it'll get there quicker if you spoil it rotten in the meantime. BTW, when you prune, cut as near to the base as you can get, otherwise you risk the cut stem wasting its energy re-sprouting from the cut all bushy and stunted.

We have a Phyllostachys Nigra which is a well established clump, planted in a slate area, after the first year it was not watered, mulched or fed. After rain it flops a little but soon stands up again. Perhaps you are cossetting it a little, maybe it needs toughening up. Good luck.