If you don't mind using a plant native to the western United States, you could try Oregon Grape (Mahonia aquifolium.) There is a hybrid that only grows to about 2-3 feet high.

thank you for responding cjbspokane.
I would definitely consider Mahonia - I did a bit of online research and noticed repens? as well.
Have you seen these growing in close proximity to hackberry?
I would also consider them along the front of my house - no hackberry issues there, but there's quite a bit of north facing shade. I may have to start a new thread for that particular area.

thanks again

I have seen Aquilegia canadensis, Dicentra cucullaria, Hydrophyllum virginianum, Phlox divaricata, Viola canadensis, Viola pubescens, and several kinds of sedges growing right next to Hackberry trees. In my opinion Hackberry trees are pretty accommodating towards woodland plants. I think that most any shade plant would do fine under Hackberries as long as the soil is good.

thanks for responding gianslug

The viola (or lack of) were what caused me to look a bit more closely at these areas.
I noticed the same small tree growing in each area - hackberry. The area around these were bare.
I noticed tiarella and violets were having a difficult time Tradescantia too. - usually the violets grow well just about anywhere and I use them frequently. You'll see them around the outr edges of the area in question - but these bare spots don't seem to accommodate them well.

The kind folks at the "Name that plant forum" helped with the ID. I then googled Celtis occidentalis and allelopathy, and sure enough found a few hits.

I've transplanted two of the three small trees to another area of the yard - I appreciate their wildlife value, but wanted more herbaceous stuff in the area closest to the house.
Rather than continue with my fruitless experimentation of what might work, I wanted to hear from others with hackberry and what works for them. if Phlox and Dicentra have worked for you, it's certainly worth a try here. At least I'll feel at bit more confident knowing that somewhere there's a Hackberry tree with some happy Phlox d. companions.

thank you for your suggestions

I've got the miniature holly growing directly beneath my hackberry tree here in south suburban Denver. Only prob is dry spells. There is a little die back, but it will recover with new growth. Because of late spring freezes some spring blooms are better than others and it took ten years b4 I finally got hackberries. Oh the joy that year! I also grow lowbush three leaf sumac (the smaller variety). It does well here. Great under canopy plant.

One website that I found said that hackberry inhibited the growth of grasses and other shallow rooted plants. I was interested in your post because I just planted a small Dwarf Hackberry (Celtis tenuifolia) that I bought at a wildflower sale.

I have native Chokecherry growing like crazy in my Hackberry woods. The birds get most of the cherries but leave enough so there is a continual new supply.

I have a small sumac grove under my hackberry, also Virginia Creeper and have just noticed that some poison ivy has sneaked in. However, I have lots of huge wild violets growing there too. The sumac foliage is spectacular in fall and the birds love the berries all winter.

Not quite on point, but around my property hackberries are the number one self seeding tree, bar none. Birds must help distribute them because they come up everywhere. I have nothing against hackberries, mind you, many species eat the berries. I have never noticed them inhibiting growth of anything except grasses & then only in deep shade. Smaller trees such as dogwoods & redbuds seem to thrive under hackberries as do all sorts of vines-poison ivy, Virginia creeper, sweet autumn clematis, wild grapes. Of course non-native invasives also thrive under them if given half a chance-garlic mustard, japanese honeysuckle & privet at least until the shade gets too deep.
Susan