My elm has been a stump about 2 1/2 years. I covered it with plastic, and loaded woodchips on top. After about a year, I removed the black plastic. Since then, a lot of the neighboring groundcover myoporum grew over it. This summer an elm sprout emerged, so I recovered it with a lot more woodchips. After the resprout and the dry summer, the myoporum started to look really bad, it just couldn't compete with the other( close by & alive ) elm tree's roots. So I added even more wood chips and some horse manure, in a similar mad scientist, or just experimental fashion, as mentioned by border barb. Now I planted succulents on top of it and added some rocks to make it look like a more naturalistic raised bed.

You might try corn gluten meal, as a grass killer. Lay it early as a pre-emergent, and reapply if you get sprouts. Not supposed to be poison for animals or birds, since it is almost regular corn meal. Garden sounds interesting, lots of fun for the cats. Geraniums might be of interest, not poison. They come in many sizes of tiny to large. Huge selection in flower colors, scented leaves and leaf shapes. Apple, rose, lemon, orange are scents that I have smelled. Put them where you will brush against them to release the scent. Bloom almost all the time in full sun. Pergoliam is the Latin, I think, which they might be listed under. They were real popular in Colonial times for scented leaves used in potpourri, flavoring food. Mine are floral, but the cat here does enjoy biting the leaves at times, sitting in front of the french doors in the sun. She also likes the Rosemary plant topiary! Nasturtiams are edible though not my favorite flower on food. Kind of a peppery taste when we ate them in a salad. Flowers are pretty, bright colors, like the sun. Martha Stewart sold seeds for a climbing variety, but mine missed the fence, just crawled around. Foliage is cute too, round leaves. Chrysanthemums are edible, very popular in Asian food. Japanese or Chinese, can't remember. They sprinkle the petals in soup, salads. Should be OK for a cat to chew on. Many shapes, heights, colors to choose from. They flower better with pinching tips back until 4th of July. You get more blooms on sturdy, shorter stems. They are perennials, can return each spring. Mine tend to be shorter lived, but other folks plants live for long times. Two of the flowers I named are annuals. Geraniums can be saved as plants over winter, dry in the dark basement or potted in front of windows over winter. Nasturtiams are available by seed in spring or you might be able to save seeds from this years plants.

If the material you applied contains glyphosate as the active ingredient, as most Roundup formulations do, and you followed label directions, it should not be affecting your tree in this way. Once it hits soil, glyphosate is not herbicidally active. Of course if it drifted off target or you applied it to the leaves, or green bark or branches, or sprouts of the Bauhinia it will be taken up and cause problems. I'm not familiar with the other herbicide you mentioned. Other herbicides can definitely move up in rootzones, even those used for selective weed control in turf such as dicamba.

Toxic in what regards? If it kills weeds, then it does have some toxicity. Unless it is horticultural strength (20% or more), vinegar is a very ineffective herbicide and generally requires several repeat applications and even then will not kill off brush or any perennial weeds. And if it IS of horticultural strength, it is quite toxic/caustic, requiring protective clothing and goggles. Note: vinegar is not approved as a pesticide under law so application directions may well be lacking. Your least toxic method may be to mow the weeds/brush as short as possible and either till into the ground and cover with a layer of wood chips or just smother the remains with the chips.