I've used paving stones (flags) to create a root barrier. When I dug up
the garden there were tree roots just below the surface emanating from a
row of trees that were planted about 20 years ago. Don't know what
trees they are, but they are those fast growing evergreen types. Look a
bit like Christmas tress.

Anyway, the flag barrier is 61 Cm deep(2 ft)from the surface of the
garden. But, between sections there is a gap between the flags of about
4mm or 5mm.

QUESTION: Do I need to plug the gaps between flags, or will I be okay
leaving the gaps? Thanks.