Of all my clumpers, Bambusa chungii has the longest internodes. Some are three feet in length.

A more cold hardy clumper that has long internodes is Bambusa textilis, but be sure you don't have one of it's varieties, which are smaller.

The textilis can stand temps here to 15F with only leaf damage and some top kill on the culms, so it can surely survive colder temps, but mine haven't been through any colder temps...yet. The chungii has only been through temps down to 26F with no damage.

Both grow culms over 1.5 inches in diameter, with textilis being a bit larger.

Bambusa Oldhamii has some internodes that are 16" but some are shorter and the bamboo is not very cold hardy here when temps get below the low 20's. However, it has thick culm walls which is good for construction.

There are many others to consider, but most are not cold hardy enough for your area.

Remember, plants that have to 'reach' for sunlight, as from competition from surrounding plants or buildings, will make the internodes grow longer, also. A plant that is in full sun, with nothing around to block sunlight, will grow shorter.

Textilis would be my choice since it is my most cold hardy of the large clumpers, reaching 40' here.

Good Luck

Kt

I Agree with kentuck8b. I have textilis with very long internodes. (20") I dug this large clump from a friends big patch. Clumpers are tough to dig! I Just went through a week of 21 to 26 degrees all night with little color change to the leaves.( I think the change was from the 50 mph winds. So Textilis is pretty tough as a clumper with long internodes. I don't know about zone 7? sounds pretty cold. Might get a complete regrowth each year.I've seen large Olhamii freeze to the ground and comback the next year around here. 10 degrees. It's 4 inch diameter.
Good luck. but in zone 7 you might look for long internode cold hardy varieties.