Originally Posted by echinosum

1. Existing culms never grow any more once they have expanded in the year they appear.
2. Your drooping bamboo looks perfectly normal. The upper part of the culms are light and airy and will tend to bend over like that. This is a characteristic of the species. Some types of bamboo are droopy, some are stiffer. Looks just like the P Bissetii this guy is selling, which he describes as slightly arching http://www.uk-bamboos.co.uk/Detail-B...s_bissetii.htm But a lot less arching than this "fountain bamboo" http://www.uk-bamboos.co.uk/Detail-B..._murieliae.htm Why not use a bit of string to keep it more upright? That's what I do with my fountain bamboo.
3. The new bamboo you bought that doesn't droop, I rather suspect its a different species, isn't it?
4. You appear to have planted the bamboo along the property boundary. If you don't wish to annoy your neighbour with bamboo sprouting up in his garden, it would have been wise to put in an underground rhizome barrier to along the property boundary to contain it in your garden, to a depth of about 50cm. Thick HDPE sheeting 50cm wide is sold by bamboo specialists for this purpose. You can also make your own of masonry, cement, etc. Phyllostachys are running bamboos, and though they are nothing like as rampant in Britain as they are in the warm wet sticky summers of their native origins, they can spread about quite a bit, especially once they have been in the ground a few years.