Growing on shingle

Have a good look around the margins of the pebbles to see if there are any signs of nasties like horsetail that might have been covered.
There is also a chance that strong long lasting weedkillers might have been applied before the weed control fabric was put down.

I used to grow strawbs on gravel through the weed fabric with no problems apart from woodlice and slugs living inside the cut holes.
A few slug pellets soon cured that problem.