When plants were invented, it's not as if The Great Creator assigned a proper spacing to each one. A "proper" spacing is determined by man in light of how useful he can make a plant be, in order to solve his needs. Therefore, it is the situation or yours and the site conditions that will guide one in determining an optimum spacing for the Hornbeam. Though you describe briefly some of the conditions, it's not clear how they exactly are, and a picture (that is not a close-up) will help those who cannot see it in real life, understand. We don't know what plant a "hedge row" is, so how the shade of the Hornbeam will affect it cannot be determined. Need that picture for more information.

The use of this tree as hedge material is not something I've seen done personally, but anything is possible so long as you know what maybe involved. In this case, quite a bit of pruning. I'm assuming you are after a "clipped hedge" sort of look-correct me if I'm off-base on that assumption-and as such, much pruning. The second question is a bit more in my wheelhouse. Very simply put-this is, after all, biology-plant growth hormones produced in above-ground growing shoot tips send chemical messages to roots, telling them when to expand, etc. The removal of many shoot tips will reduce a plant's root growth, so you're onto something. What I can't do is quantify this for you, varying as it does by species, growing conditions, etc. That's about all I've got at the moment. +oM

Because Hornbeams are supposed to be so resilient and they grew during the spring, I didn't worry about watering them as much this year. ==>>> 3 to 5 years for 12 foot trees to get over transplant shock ... and i would continue to water them for at least 2 more years ... reducing it each year .... frankly.. they look just fine.. considering 99% of their roots were cut off a year ago .. never forget.. most of the growing is going on in the root zone ... so i would be glad they look as good as they do ... they are stressed.. not hungry.. no fert ... what has been your ambient weather since planting.. including winter.. did you water at a reduced rate in winter.. or at least check soil moisture??? im not familiar with your zone ... and where are you.. z7 is kinda vague ... ken ps: i am in 12 weeks of drought.. all kinds of trees are shedding leaves to some extent.. its normal.. i figure they just sacrificed some of the canopy to cope ... some leaf loss in august is not that big a deal ...

I know what it looks like, didn't thrash my way through the shrubs between me and it to look for labeling. Because for one thing the site tends to have signs listing what plants in each section are rather than individual labeling. (I don't remember now if one of the signs mentioned this tree, I was there with somebody else and we viewed, talked about multiple different theme plantings with dozens of different kinds of plants in them). With European hornbeam except for certain apparently smaller than typical selections such as 'Globosa' (28 ft. tall at the University of Washington by 2005) and 'Pendula' one is always dealing with what is a tall (60 ft.+) tree genetically. With as always with trees there being variations in what occurs over the same periods of time due to differences in site conditions. For purposes of illustration sub-alpine fir is known in the wild both as a 100 ft. tree and a creeping shrub, as well as versions in between. Due entirely to the range of environmental factors within which the species occurs naturally.