As stated in the previous posts, the appearance of these types of mushrooms on a black locust is indicative of heartwood rot. And heartwood rot is incurable. The tree is dying but may take a number of years before it fails completely. The immediate concern is that trees with heartwood rot are structurally unstable and prone to wind breakage and dropping limbs. I'd consider removal if sited where it could fall on the house, cars or passersby.

Contessa, if these sprouts are in the lawn, can't you just mow them off? Just trying to figure out your situation here-there's nothing less fun to do in the garden than deal with root suckers! The "burn-down" products will offer no greater duration of effect as compared to glyphosate. And now, understanding that you prefer organic means, I'd rethink the two synthetic options there anyway. In fact, I'd be danged if I'd ever purchase any paraquat! Icky stuff for sure. So perhaps just a bit more background info on this situation; Are there different tree types doing this...do you think? And also, has any pruning or other work been done to the neighboring trees? Nothing sets a colonial species (one which will form many root suckers) up for heavy sucker production like being pruned. A tree reacts to having branches removed by making more branches! If it happens to be a colonial species, each individual "tree"-actually a ramet-will act this way too. Maybe seek to determine what species are in play here. We may have more specific advice then. ps......or maybe, (me) re-read the title of the thread! Black locusts-got it. Yeah, that's a bad one for root suckering. This is one of the means by which black locust invades forest lands where it doesn't belong. I hate this tree. You're going to have to try one of the ideas already offered......if these tings are coming up somewhere other than your lawn. If in the lawn, just mow them off.

Foliage aspect seems different but it does look at though it has the dark and hard thorns of that one.

Where are you located? Where I am, little survives in a pot over winter unless the pot is buried in leaves, mulch, or heeled into the garden. It won’t do well over the winter indoors, so depending on where you are, some type of protection in an unseated building or with the pot buried somehow may be needed. This would protect the roots from extreme cold and mitigate temperature swings since the mass of soil or mulch changes slower than air temperatures.