Those are definitely important things to consider before planting. How large an area is it? Level or sloping? In addition, hydrangeas prefer acid soil while lilacs (in my limited experience) do better in neutral or alkaline soils. I dump ashes from my woodstove on my lilac every year to neutralize the soil. A slow grower shrub you might also consider is daphne depending on the drainage. Weigela is another pretty spring bloomer that's relatively low-maintenance and there are several dwarf varieties available with attractive foliage. Mine grows well & blooms profusely in a part sun area. While I do water my hydrangeas during dry spells, none of my other shrubs get any supplemental water. Caryopteris/blue mist shrub only grows to about 3 ft. and it's also low/no maintenance. It blooms late summer/early autumn too plus it attracts butterflies. It does want plenty of sun. According to my notes, mine bloomed 3rd week of August right through 2nd week of September. A couple others you might check out that could adapt to your growing conditions are Spirea japonica and Pieris japonica. The pieris does best in part shade from what I read.

I passed this average, run of the mill horse pasture this morning. You will notice that the field is dominated with buttercup which is one of the plants on OP's link. The horses simply eat around the weeds. Should we pay attention to livestock pasture, by all means. Pastures should be limed, mowed and tend to the weeds. Having said that, its not realistic that all the plants on the Univ of Idaho link can be eliminated from the pasturefield. Skunk cabbage is in every wet area of every pasture I've ever seen. I know of nothing that eats it. Protect your horses from biting insects which torment them and protect their eyes. Provide livestock with a salt block. BY ALL MEANS if you are gonna plant a new tree in the pasture protect it with a fence. You know what cribbing is, consider the damage horses can do to a new tree.

In a similar situation (with some parts getting a tad more sun than you and some parts a tad less) I have many daylilies, veronica, shasta daisies, asters, phlox, perennial foxgloves, helenium, geraniums, echinacea, penstemon, solidago, hellebores, coreopsis, rudbeckia triloba and (I think) Herbstonne, scabiosa, lupines, bleeding hearts, monkshood, astilbe, lilies, and liatris. I also let columbines, feverfew, campanula, and Queen Anne's Lace reseed (I know some think QAL is a weed but I love it!) All of the above do well although the helenium is new so not sure yet how that will do. I also have reseeding nigella, larkspur, and few other annuals that are left over from my market-selling days. I let these reseed and they seem to do well in the part-sun gardens. For shrubs I have weigela, flowering almond, carolina allspice, hydrangeas, deutzia, boxwood, hollies, spirea, quince, and a couple of roses that are doing okay, not necessarily thriving, but that may be due more to my neglect than their situation. I did plant a Lyda Rose in a friend's garden in similar conditions that is spectacular! And I have a Darlow's Enigma in almost full shade that is doing well. Red or yellow twig dogwoods may work too. One of my gardens used to be a shade garden till we lost a beautiful oak, and there are hostas in it. It still gets some shade, but the first two summers the hostas fried (I didn't move them because we had planned on getting a new tree but life got in the way!) This year I am determined to give them more water to help them along, and so far so good, including this last week of 85 degree weather and no rain for weeks. The hard part for hostas here, like for you, is the direct afternoon sun. If you have sections that get morning or later day sun hostas may work better there. If you go with astilbes they may need supplemental water as well. I also have put in dahlias last year and this year. I did the flowers for my daughter's wedding and planted almost 100 tubers last year, and even with leaving some in the ground to die and losing some over the winter in storage, I still had about 85 tubers this spring. I don't have any "full sun" conditions at all, and in a weary attempt to get all those tubers planted this spring I had to put some in somewhat shady conditions so I'll see how they do. The ones last year in part sun did quite well (I converted my vegetable garden, the sunniest spot, for the dahlias last year. This year it's back to veggies so dahlias are roughing it lol) But many are in the same part-sun conditions as last year and they did quite well. Depending on moisture levels in you garden, itea, clethra, cephalanthus, salix, and viburnum may do well. I take care of a friend's garden with similar sun conditions but it's practically a swamp, and these thrive there but I think they need the high water levels. She also has ligularia in here, another moisture lover. Surprisingly, peonies and hydrangeas do well, and I would think this soil waaayyy too heavy and wet, so maybe the peonies would work for you too. She has another plant here that I can't think of. I want to say sambucus but I'm not quite sure, and so not quite sure if this one needs lots of water as well. I also like to supplement some bare spots with annuals. I never did many annuals till I started selling at market and now I love so many of them. I always have zinnias, and annual rudbeckias, and I also like cosmos and cleome. Sorry, didn't expect this post to be so long but kept thinking of more stuff! Hope this helps! :) Dee

Bump!