Pretty lilac, especially abloom. I'm no expert on their form or fragility, having only had them as shrubs in my yard as a child. The look of the leaves is a little soft for me, aesthetically, but that's a personal take.
I've been looking over some past notes, so as not to reinvent the wheel.
I see I mentioned broken concrete walls, before; they're quite easy to build if one has a source of broken concrete pavers, but I think that's a no for your area, swimpy.
On trees, a few clips from past comments -
-- from page 6 and 7
Eleagnus augustifolia russian olive (considered ia problem many places/osso)
*Malus flowering crabapple
*crabapples, and flowering quince
asterisks those I want to check..
--- crabapples - One with high disease resistance that goes to about 20 ft. at maturity is Malus Strawberry Parfait, seen HERE. There's another one called M. 'Sugar Tyme" that has white flowers, gets to 18 feet by 15 feet wide. (also with high disease resistance).
--- Actually, all those on that Frank Schmidt link look interesting, even the tiny M. sargentii 'Tina'.... I'd check its disease resistance though, as Sunset lists sargentii as merely having "good disease resistance" (choices I see are fair, moderate, good, and high).
--- Well, Pyrus kawakamii doesn't have fruit either - I had one. Somewhat more attractive form than the Bradfords. Was always worrying about fireblight... - not sure that is a problem in Iowa.
-- If you don't want fruit, hmmm. Maybe a Crataegus (hawthorn). They have berries, but I didn't find them any big deal. The hawthorns can have a very nice standard form, take pruning well. They do have thorns, but I didn't mind that. I had a row of washington hawthorn trees (in standards) back in northern CA; I liked them a lot (they take wind...). They could also be in groves, or, say, sets of three (picture sort of isoceles triangle points).
-- I haven't looked up what non fruiting Prunus trees would make it in Iowa....
-- haven't looked up quince, speaking of fruit
-- wondering where I got that mention of cornus being ok for iowa..
I also had some Laurus nobilis trees (saratoga) - a lifetime's worth of bay leaves. Wonder if they grow there..
Wonder if persimmon makes it. Probably not, besides the fruit. I just have liked their shape and leaves (gorgeous one in front of a Neutra house I did a garden plan for).
Never mind, I have some googleing to do.