At the base of our old garage where the concrete foundation meets an asphalt slope down to the alley behind, we've had small elm tree saplings grow as weeds over the past three years. I've never managed to pull one out when they are very small, and instead had to clip them down at their bases. Each year they regrow from the same little stumps, more and thicker new shoots.
Since I cannot dig them out without tearing up the asphalt, how can I permanently kill the roots left there after I've lopped off all the shoots and cut the little stumps down as near to the concrete as possible?
A salesperson at the home center suggested concentrated ground clear, but I wonder if there's something less drastic I can use to target only the sapling stumps. The area is not in proximity of any other plants, lawn, or where children might play.