Ben, I did a "black walnut toxicity" search and this is what I came up with. "There are lists of juglone-sensitive and juglone-tolerant plants in the Purdue Extension publication "Black Walnut Toxicity" (HO-193-W). Ask Purdue Extension office in your county for a copy or find it on-line at http://www.hort.purdue.edu/ext/HO-193.pdf . See the links at the end of the publication for more plant lists. Following is a list of plants you might try growing under walnuts. If you see them decline, move them or lose them! Landscape plants: arborvitae, autumn olive, red cedar, catalpa, clematis, crabapple, daphne , elm, euonymous , forsythia, hawthorn, hemlock, hickory, honeysuckle" and the list goes on. I've seen those roots extend 90' from the trunk and wouldn't doubt it if they go further. noogy

We ordered 300 Tundra and Borealis from Canada in September and distributed about half of them to other local green thumbs. The plants spent a week in transit but were still moist upon arrival. We gave a couple of bushes to a relative in Albert Lea, MN, and look forward to seeing how they do in the rich soil down there. I just talked with a grower (not a seller) in Saskatchewan this evening and he verified how sweet the Canadian berries are that have been cross-bred at the U of S. He said that the Russian Berry Blue (the pollinizer) is fine for processing as you can add sugar, but both Tundra and Borealis are great off the bush. We plan to order another shipment from Canada in the spring of 2011.

www.prairienursery.com - sells a septic field mix of native grass and wildflowers - they are good for septic systems and i think their mix stays away from deep tap rooted plants and consists mainly of deep fibrous rooted plants - which are better for the septic field ...

I would also opt for something other than the oaks. If you are still going for a native tree I would choose the native hybrid Aesculus 'Homestead' or the Homestead Buckeye. It is resistant to the common leaf blight Ohio Buckeye has at the end of the year and is perfect for a prairie setting with outstanding orange fall color and a perfect rounded crown. Another great choice would be Aesculus 'Autumn Splendor' which is a University of Minnesota release that has red fall color. Both trees will mature in the 20' range and are resistant to the leaf blight that commonly disfigures other buckeyes and horse chestnuts. They will produce fruits so are not recommended right by a sidewalk. Other options would be the dwarf river birch Fox Valley or Little King, and you could also do Blackhaw Viburnum (Viburnum prunifolium). There is also a dwarf oak release from NDSU called Prairie Pioneer which is more of a single-stemmed, non-suckering dwarf oak. Only problem is that it is very hard to locate in commerce and I have never seen them available for sale. If you wanted to go with something non-native there are two newer Ussurian Pear varieties, Mountain Frost and Prairie Gem. Prairie Gem would give you a dwarf tree in your range. Overall I prefer the buckeye as it has that "native look" and you probably won't find them planted nearby.