You can find Lots of TB pics at Snowpeak (hot link below) and to see Dutch iris, which grow from bulbs, do a google image search. I have heard zone 6 is too cold for Dutch iris to naturalize as kprp says. As for differences, Dutch iris take less space, are shorter and are wonderful cut flowers for mixed spring bouquets. TBs form much larger clumps, are much taller and aren't too great for bouquets. One stem is quite dramatic but make sure it isn't one that 'drips' after cutting. Here is a link that might be useful: http://www.snowpeakiris.com/newweb/navpage.htm

Like any other bulb, each bulb is an individual plant and while they may naturalize (and I've never seen a bulbous iris accomplish this to any significant extent), you will never get a clump 5' across! What you are describing are NOT Dutch iris! Pictures would help, but yours sound like Siberians. Dividing is recommended in the fall for these as the bloom cycle will be less affected, but it can also be done in spring. You may just miss a season of bloom doing so then. I've grown an awful lot of different Siberian (and Cal-Sib hybrids and other species) iris over the years and they tend to die off in the center as the plants age, leaving a doughnut of active growth on the outer perimeter. I've had the best success dividing by using an old pruning saw to slice the clump into manageable pie-shaped wedges while still in the ground, then digging and removing them. You'll want to remove and discard the old inner portions as these will not produce. FWIW, there are countless species of iris and many dozens of hybrids and these include bulbous, rhizomatous and fleshy rooted forms. They all get handled a bit differently. ps. there are no "rules" of plant division - only guidelines :-)

No squirrel problems with mine. I have big patches of Harmony and Pixie, both dark blues, and another of Springtime, a two-toned blue. Mine bloom very early, a few weeks before my crocuses bloom. They have returned well over the past 3-4 years. (Another similar iris, Iris danfordiae (golden yellow) that I tried between the blue patches was much less successful.) A small warning - just so you can take it into consideration when deciding where to plant yours - Iris reticulata foliage is not as clean as most minor bulbs are. After bloom the iris put up tall very thin blue-greenish foliage, usually just one stalk per bulb. It elongates from a couple of inches to about 12 inches over a period of a week or two and takes awhile to die back. The foliage is not heavy looking, but if you have a lot of bulbs as I do, it is quite noticeable. I have my Iris reticulata in a bed of small daylilies. The daylilies do not emerge until weeks after the Iris is done. Once the iris foliage gets limpish I take a couple of minutes & sort of tuck it under the growing strap-like foliage of the DLs. Once the iris foliage dies the daylily bed looks like it is mulched with a thin layer of very long pine needles, which eventually disappears by mid summer.

Have been grown commercially in the Skagit Valley in the past, but were dropped after a record winter. Don't know if there is any current local production. We have grown them for a time more than once over the years in the garden here. Like other spring bulbs tend to dwindle and disappear, this may just be lack of adequate fertilization. Do seem to have a consistent tendency to produce stippled/streaked foliage here, don't know if this is thrips or if they are coming from the suppliers virused. If there is a virus problem with stocks on the market it would seem that could also contribute to lack of persisting vitality and permanence.