Some years ago,my neighbour decided to have block paving put down for parking.I had a flowering cherry tree whose roots ran onto the piece of land being paved.I assume poison was used because the tree died so l cut it down.The stump is still there and when I have planted various new perennials they have died.The paving was done probably over ten years ago!Will this piece of ground ever be clear of the poison?By the way,I am on good terms with my neighbour.

It would help to know what chemical was used under the paving. Since you are on good terms, perhaps your neighbor could tell you.

Its called herbicide persistence and could last for years. Weather (wetter the better) and concentrations of herbicide both play a big part in how long the herbicide will last. One remedy is to plant a cover crop of some sort, let it mature, then pull it out and toss it in the garbage. Keep doing that until the herbicide is neutralized. Its called biodegradation - the idea is to get enough microorganisms into the soil to 'digest' the herbicide.

I've heard it called bioremediation, or phytoremediation.
https://land8.com/5-best-plant...

But when the issue seems to be soil sterilant herbicides...
https://www.mrt.com/news/artic...

Not sure there is a solution.

Of course, this is assuming there really is herbicide or other toxin.

Ask the neighbor.

I agree that you should ask the neighbor what, if anything, was used. Its possible that there is still some herbicide residue under the blocks that is gradually leeching out.

If they did use an herbicide and you think it is trapped under the blocks, deep watering the driveway multiple times might drive it out. Of course you'll have to consider any local watering regulations before watering a driveway.

You might also consider other toxins that are spilled on the driveway. Fuel or car cleaning products might be causing the ongoing problems.