It looks like psuedosasa japonica which is a miniature running bamboo. If you want to cut it back to control it, I would suggest cutting down all the unwanted culms down to soil level, dig a trench around the area that you want it contained, and keep the area where you don't want culms mowed.

I agree: Pseudosasa japonica...a runner.

Ugh. Not what i wanted to hear.
What do i put in the trench? If i cut it back inward 5ft around the whole parimeter will that make the rhizomes grow outward faster?
The thing i am.worried about most is one side of it is boarderd by woods, if i dig a trench and somehow some of it gets into the woods it will be hard tocontroll.
I am very suprised in how little it spread in the last 20 or so years. But to be honest i am not sure what i am going to do about it. I like it, but i dont think i like it enough to care for it like it needs.

If you are in the northern parts of NY like I am, most running bamboos only spread inches to a couple feet per year due to the cool summers so it is reasonable to expect very slow spread.

What I meant by digging a trench was literally breaking all the rhizome connections which shouldn't be any more than 6 inches deep, and then filling it back with soil. A pick and a lopper should work fine, but I would suggest waiting until after a rain storm so the soil is easy to work with. The severed sections of rhizomes cannot continue to spread, and they may send up survival shoots, but their shoot buds and energy are limited since they don't have a source of energy. The survival shoots will still require a decent amount of direct sun to survive, and cutting the survival shoots with a lopper or pruners to soil level a few times over a few months will kill off the rhizome without having to dig it out.

If shooting season has just occured, severing rhizomes from their mother culm can often kill off the rhizomes completely depending on the species because all the starch in the rhizomes have gone into the new shoots, and there is very little energy left in the remaining sections of rhizome, so they rot off.

I've attached a link of some of my bamboos, and even though they may not look like it, they are all running bamboos.

Here is a link that might be useful: Running bamboos in the ground

Thank you very much for all that info! I am on Long Island, althought I am further south than you, the ocean usually keeps our summers milder than inland. As for the trench... what I have done so far this year (before finding out its a runner), was I went to the furtherest "clump" of culms and used a mallet to carefully dig them up. When I lifted them up I was able to follow the rhizome back to the next "clump" towards the main grove. I was also able to see if the clump I dug up had a rhizome that was underground leading away from the main grove.
Ideally I would like to get this grove to about half the size... maybe take 5-8ft off the entire perimeter. A couple of questions:
Can I plant grass ontop of the lopped culms? I know the roots are so shallow, I am not sure if I will be able to grow "regular" lol grass ontop of the dying/dead roots.

If I wanted to dig up and completely remove the 5-8ft off the perimeter I would do it over time (a month or so). Would it be best to cut all the culms back at once to where I want them and then dig them out over the course of a month or two. Or would it be better to just cut down a few clumps of culms and then dig them right up? I guess I am just worried if I cut down the culms to the area I wanted, would the bamboo go nuts sending out rhizomes?

Thanks again for all the help. I spent 6 years in Hawaii and grew to love bamboo, but we have a pretty big yard with alot of stuff going on already (pond, garden, veggies..etc) So I dont really have time to maintain a 30' bamboo grove.

If new shoots are just finishing their growth as it appears, I think it would be best to get rid of every culm that is unwanted, and then severing it from any connection to the existing culms with a pick/shovel/ lopper because the rhizomes are probably at their weakest. If you wait a month or 2, they might recharge a little bit, and re-growth may occur from the stuff that was cut down and severed from any source of photosynthesis. I would also suggest using a lopper and thinning out some of the smaller culms in the clump that remains just to reduce its water requirement which should help it look a bit healthier.

If you have literally a solid mass of roots, you might have to wait until it breaks down a bit before planting grass, but if there is soil and enough sunlight, I don't see why you can't plant grass back in the area. Just make sure the culms are lopped all the way to soil level to they cannot damage the blades. The thing is that most bamboos cannot grow nearly as low as grass because of their limit on the number of buds, and a minimal size they can effectively produce regrowth.

If you are in Long Island, you are in a much warmer zone than where I'm at, perhaps by around 7-8F with a lot more sunshine so a lot of running bamboos should be able to spread aggressively to some extent. You might have the ideal climate to grow clumping bamboos instead given you are probably around a zone 7 with mild, but not hot summers.

How can I tell if the shoots are finishing their growth?

So a good plan of action would be to cut back the grove toward the center to where I want it, and then dig a trench just to the outside of the grove seperating the culms I left and the culms I have cut down... then I can take my time digging up the roots of the cut down culms? And when you say blades... you mean the lawn mower blades?

I dont want to erradicate it just yet because this bamboo was given to this property a long time ago by a pretty well known Long Islander.

The first two winters after we bought the house were absolutely brutal with cold and snow... maybe that is why I havent really seen this stuff spread much yet... maybe this spring will(would) have been different.

My neighbors has been kept in check by her thru digging and pruning and it is so much smaller than mine lol.

We are definitely warmer here, but we have alot of low cloud and fog from March to May because of the ocean.

They are pretty much done with their growth right when the branches stop growing, and new leaves are starting to come out of the branches which can provide energy pretty soon if you let them leaf out. The shoots should start feeling solid by this point.

If you get a strong lopper at your hardware store, it should take care of a grove pretty fast. A reciprocating saw or chainsaw would be even faster, but that would be overkill for containing a small grove like that. I would suggest first cutting down the culms that you want to get rid of, to kill off the energy production, and then dig the tranch around the grove that you wish to leave alone. You can then take you time and dig out the rhizomes if they happen to be in the way of something you want to plant or if there are tiny survival shoots.

I did mean lawnmower blades. If you don't cut the culms down to soil level, and leave 2-4 inches of stump, they could dull out your lawnmower blade when you mow over the area. It's not really the cold that prevents them from spreading. It seems like it is either drought or cool soil temperatures over the summer that limit their spread.

I just came in from outside... its horrible here, cold and drizzling. I spent about 1-1.5hrs going around the entire perimeter cutting down culms. I cut from 3-5ft inward on average around the entire grove. There were a few impressive shoots 4-6ft tall... however most shoots were under 4-6" tall. I would say over 90% of new shoots that I see coming up are within a few inches of existing culms. That makes me feel a bit better about the running rate of this bamboo. The grove does look better already, it looks a bit more upright than it was before. I will probably go out there and trim it in another 3ft or so all the way around and then dig my trench. I have to see how much the wifey wants me to trim back first before I trim too much, lol.

I got rather lucky... my 30lbs australian shepherd runs around and around and around the grove all day long... it used to make me wonder what is wrong with her! lol. However I now have a 3-5" rut around the entire grove which is how I was able to see the rhizomes in the first place, lol. Who would have thought.

Any tips on how to get rid of the cut culms? They are a pain to transport in the back of my truck while they are still green, the leaves take up so much room. After they are cut, how long does it usually take for them to lose there leaves? a week, a month, a year?

If you don't need them, you might be able to put up an ad on craigslist, and somebody will want them, even if they are still fresh.

They take about a month to lose all their leaves, and perhaps another month under full sun to dry out and be used for crafts/building materials. The size you have appears to be ideal for garden stakes so someone will want them.

Again, thanks for your help.

I was rather surprised that once I started trimming and got passed the outside of the grove, some of the culms were pretty impressive. ~15ft tall and almost 1" in diameter.

That's not bad.

Some of my bamboo groves are showing shoots around the 1.25 inch mark this year so far, and I'm hoping to get some of them over 15ft tall.

It's very exciting to have a very large species of bamboo because it is cool watching them rise a few feet every day.

To be honest, I haven't paid as much attention to it as Id like. Like I said before, I have so many other things going on that I haven't tended to it at all really, and haven't enjoyed it. My dog loves running through it though!
I was nice getting out there with the loppers. While getting in the grove I was able to take a look at how many shoots did come up this spring, and got to see a few of the shoots that were already 4-5ft tall and hadn't opened yet! They easily get lost when you look at the grove from afar, but you can see whats going on much better once you get in there and work.
I think I am going to trim the leaves off of them and bring those to the dump, and keep the poles to let them dry out. My father in law wants some for cane poles, and maybe Ill throw them up on CL to see if anyone wants them for garden stakes. I didn realize how much they cost! 75ft of garden stakes is ~$25.