Any you don't want can be cut off without killing the clump. Don't, of course, cut all new shoots off every year or the stand will eventually fizzle out.

I would think the sideways shoots would grow vertically before they got very tall.

There is a bamboo forum also.

I cut off sideways growing shoots as soon as I see them. They never straighten up and stay there. It's Bamboo's way of overpowering it's neighbors and enlarging the grove.

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This formerly upright Timber Bamboo tipped over and never came back up. They broke off underground.

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Sideway growth is usually a rhizome that has surfaced for whatever reason, perhaps a buried rock, a wall, the edge of a container or ? Rhizomes will take the path of least resistance and are generally in the top 6-12 inches of soil. When they are diverted upward to daylight, they leaf out. The only reason you might leave this type of growth is if the plant is young. When small they need all of the growth they can get as they established to eventually look like Botanns awesome grove. :)

I rather often encounter growths on top of the ground that consist of a rootstock with a shoot-like, pointed end. There may be little anchorage of the outer part, approaching the sharp tip. When these are pointed at asphalt paving under my jurisdiction these are broken off, before penetration occurs.

Thanks for the help, As the groves are quite new 3-4 years I think I'll leave the side ones so far as sure don't want them to tip over. Finally seeing some big healthy new shoots this last weekend. Seems very late must be the cold and rain.