The mowing will maintain the perimeter with regards to culms, so long as you understand the rhizomes will go out well beyond the grass. If you are going to try to maintain a trench, why not concrete the trench and create a solid barrier. I personally like my boos intermingling. Seeing big viridis culms interspersed through my nigra is attractive. The USDA collection is contained with concrete footers surrounding each plot. Some runners do jump ship, but are easily pruned at that line. I hope my input is of any help.
Chris

in the same situation, i would be inclined to build raised beds or mounds, leaving 'flat' ground in-between each bed and at the edges. you'll catch the significant majority of the escaping rhizomes and can easily prune them, plus the bamboo will enjoy the beds. it may be a matter of personal preference, i prefer dry stacked stone walls or rr ties to trenching. the rhizomes easily find their way between the stones or the ties, so they do not tend to go deep to avoid them.

cmontross and inversa, thanks for the advice. The main reason for me digging the trenches and keeping the 'boos separated is because I'm afraid of one species overtaking and choking out another. Since I'm in a much colder/less ideal climate for the bamboo, I am expecting a couple to do really well for me while the others trudge along. I don't want the ones that do really well to overtake and choke out the others that aren't as vigorous because of my climate. Am I right to expect this, or would allowing them to intermingle not be a problem?

As far as mowing the thirty foot perimeter: will culms shoot up outside this area? I was told/read that the rhizomes would continue to grow out into the mowed area, but would not spread too far past it since they were not able to establish culms within the mowed area itself. Is this correct?

The species I chose are, in order from 1 to 6 in the original picture I posted, P. atrovaginata, P. nuda, P. nigra 'henon', P. rubromarginata, P. aureosulcata 'spectabilis', and P. dulcis. I like the idea of making raised beds, but with six planting areas each being 20' wide and 25' long, that would require a few dump truck loads of top soil. Additionally, most of the above species are already in the ground, this being their third growing season.

As far north as you are it may not be a problem with rhizomes running too far, but here in the south my henon will run 20-30' a summer. At the USDA groves, runners that "get away" will run under the mowed areas between the plots and send up shoots along the edges of the other plots. You will have some on that list out perform others in your zone. Culm thinning can help keep that at bay and allow less hardy species a chance at sunshine. Ultimately it is going to be what is the easiest and most cost effective for your wishes. I thin out the culms of unwanted varieties to allow others to prosper in their respective areas and in general it works fine. The aggressive species tend to realize that that area is not a great idea, but will keep runners in the ground to feed from.
Chris

Chris, thanks again for your input. That sounds like a much better idea than digging trenches. If thinning canes will "convince" the bamboo not to shoot as much in an area where another species is growing, then perhaps I'll try that instead. My only concern was to make sure one species didn't get choked out by another. I have no problem removing any stray canes that pop up outside the 30 foot mowed area either. I'll just have plenty for stir fry and other bamboo shoot recipes!

So far, after two summers in the ground, P. rubro. is outgrowing P. nuda, P. atrovaginata, and P. nigra 'henon' by leaps and bounds. The other two species I mentioned will be planted this spring.