Torbjörn Svensson Diaz writes

Would ferns count as weeds? Do they prolifirate aggressively? If I
plant a lot of ferns in a garden will my neighbours be mad at me? Will
the ferns spread to my neighbours? I like fern-coated trees but if
they destroy neighbours' gardens I don't like them so much anymore.

Are there different kinds of ferns, some of which are suitable for
gardening and some of which are not?

Most ferns grow in clumps, and these won't spread too aggressively (and
are easily uprooted if they do).

A few ferns spread by creeping rootstocks. The most obvious of these is
bracken, which covers a lot of our hillsides and would be a nuisance in
the garden. The other creeping ones are more delicate and less
aggressive - at least the ones that grow wild in the UK.

There are also a number of ferns which are not native to the UK but will
grow well here.

Most garden centres will have a stock of ferns.

I can't think of any ferns which grow on trees which would cause a
problem. But these ferns aren't so easy to find in a garden centre.
--
Kay