We do not have any veterinary training to know what is potentially toxic to a pet, so consult with your vet or other references (perhaps the ASPCA has a list of risky plants) in that regard.

As for substitute ideas, there isn't much that stays the size you describe without occasional pruning to reduce branch height/length, which would have worked for a Buttonbush as well. (Although that might have been more maintenance than pruning some of the other options.) One native species that comes to mind for a more upright growth habit is Summersweet (Clethra alnifolia), although you may want to use a cultivar of that species, which tend to stay more compact and sucker less than the wild type probably would. They handle shaded areas well (although, like Buttonbush, they would flower more heavily in more sun) and similarly tolerate damp and even occasionally wet soil. Also like Buttonbush, they flower on new growth, so pruning in spring to reduce size as needed will not remove flower buds.

Since it appears that deer don't get into this space, some shrubs they might otherwise eat might work, such as Swamp Azalea (Rhododendron viscosum). Other ideas include Highbush Blueberry (Vaccinium corymbosum, though it might not get enough light to fruit well), and Red (Aronia arbutifolia) or Black (Aronia melanocarpa) Chokeberry. Generally, Black Chokeberry stays shorter than the Red (which, unless you find a dwarf or compact cultivar, will grow taller than 5 feet), although each of those species might sucker a bit; sucker stems can be cut down if spreading where they are unwanted. Winterberry Holly (Ilex verticillata) can do okay in shade (here too, it fruits better in  more sun), but to get berries on female plants, you'd need to include a compatible male somewhere in the yard for the bees to pollinate it with. Winterberry cultivars will tell you which is which, and also note which male(s) is best for a particular female cultivar, since some varieties bloom slightly earlier or later than others, so the best bloom overlap gets you the best pollination rate.

Since there aren't many shrubs that fit into the desired space of 5 feet by 3 feet or less, you may want to use one or more species of perennials instead. Setting aside the pet safety factor again since we can't speak to that, options for those conditions may include Cardinal Flower (Lobelia cardinalis), Blue Lobelia (Lobelia siphilitica), Turtlehead (Chelone, several species), and Blue Mistflower (Conoclinium coelestinum). Blue Mistflower can spread a bit aggressively where it's happy, but surplus plants can easily be dug out and given away or composted.

Miri

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