Phyllostachys bissetii before thinning
You could prune the big, running bamboos with the same techniques I described in How to Prune Dwarf, and Shrub Bamboos
, however, your timber bamboo would probably never get over 5'-6' high. Instead, you selectively remove some of the older, less productive culms, in order to make way for new vigorous growth. You may also want to remove some of the branches and spindly stems.
First of all, you should equip yourself with some eye protection because there are all sorts of pokys that create a real hazard when you work in bamboo. A tool that is indispensable for removing large culms, is a sawzall. It's fast, it allows you to get to the interior of the grove, and you can cut large canes with it easily. In addition, the blades are relatively cheap and easy to change out (which I do frequently). You can use a pruning saw, but they tend to bind up after they lose their razor sharpness, and the blades are expensive to replace. Loppers come in handy, but you are limited to the size of culm you can cut, and you can't open the handles to cut culm in the interior of a grove. Hand pruners can be used for removing small branches and spindly growth.
I start by removing the spindly, twiggy growth
at the perimeter of the grove, using loppers or hand pruners to cut it back to the ground. It opens things up for access, and it give the grove a cleaner look.
Older culms are more bleached
Next, I thin out the larger culms. My goal is to open up the grove and make some room for next year's shoots, and most of the culms I remove will be the oldest ones. The older culms are more bleached, (pictured right) so they are easy to spot. I start by removing those first, cutting them back to the ground with a sawzall
. If things are still too cramped, I remove some of the younger culms. The rule of thumb is not to remove more than 1/3 of the culms in a single growing season.
Note, the bamboo in this demonstration is highly managed, so the oldest culms are only 3 years old. Normally, a grove will have a lot more older culms, and if it is neglected, some dead and dying culms that should be removed first.
Next, I remove any dead or broken branches, by cutting them back to the culm
. You can also remove any branches that are in the way, i.e. lower branches encroaching on a drive or walkway. I always remove branches back to the culm, because those stubs are woody, sharp, and they hurt!
Phyllostachys bissetii after thinning
So, if your bamboo is getting congested, or losing vigor, pruning will open it up and stimulate new vigorous growth. Remember to have the right tools, remove culms at ground level, take out the oldest culms first, and take no more that 1/3 of the culms.