I am looking to curtail the height of my d. bissetti and spectabilis. I have been told to stop feeding them fertilizer. Makes sense..... but i was wondering that if I cut out the nitrogen, and just feed them Silica and potassium, would that still be ok. I hate not giving them supplements, but due to my property size, and distance from my house, a good rainstorm would potentially place the leaning boo's on my roof if they were grown to their fullest potential in the future. As of now they are 10 footers and only in thier 2nd season.

*****Also.....I was told that if I top them off at a desired height, that the culm itself would die. How true is this??

***Note: I am currently building a stringer system across the property line to keep them from weeping over too much.

Any thoughts/imput would be greatly appreciated.

topping should not kill the culm.
they will be shorter unfertilized, theoretically, but how much?
maybe if the stringer works height wont matter as much.
maybe once mature they wont weep over as much.

+1 on topping not killing the culm - just cut it right above a node and it'll be fine. Topping it will also help keep the culms more upright, as they won't be so top-heavy. The only problem is having to do this each year when it shoots...

Glad to hear that topping the boo won't kill them.

Do I need to wait until next year to top this year's new growth....so they get a chance to harden off??

Also.....is it recommended that I use a tree pruning spray to seal in the cut. Is this overkill???

No, you can top at any time after the culm stops growing (during shooting). The cane will die back to the internode below the cut, so cut 1/2" - 1" above the node unless you like seeing the dead stumps on the top of each culm . No sealant is required.

I agree with all the posts about topping not harming the culms. I would simply wait until a culm leafs out fully to be sure it wasn't growing any more. It's not a bad idea to top by making two cuts: the first one several inches above the node and a final one to clean up the stub. Make the final cut as close above the node as possible since cutting between nodes and leaving a "cup" to collect rainwater will result in unsightly rot at the top after a while. Use a sharp pruner since a dull one can shatter the culm near the cut, particularly when it's a newer culm. Also, be careful when you take your first cut that it is cleanly severed; otherwise, if a small part of the cut-off part is still attached, it can strip off the outer fibers lower down as it falls, much like bark on a tree limb can get pulled off when you are pruning.

However, no matter how you try to manipulate the bamboo with fertilizer, etc., the bamboo will continue to increase each year toward its typical species size. It may take more time to get there, but you are not going to be able to stunt it at some particular height. And, although topping can be done with bamboo better than with some other plants, I still think it is a disservice to the appearance of the plant. It's not clear to me why you are worried about the culms leaning over the roof after a rain. And the two species you have are ones that are going to get more erect as the culms get larger, anyway. Could you elaborate on why this is a concern for you?

Bamboos are often hedged. They're tough, no worry about the open cut. Check bamboo hedge in Google images. For places they need to be, they look very nice there.