In article ,
says...

On Mon, 6 Feb 2017 11:37:30 +0000, Broadback
wrote:

I have an area of garden,about 50 square yards, which I would like to
seed with wild flowers. Preferably ones that will reseed in later years.
How much will I need and where is there a reliable source? Thanks

Can't recommend a source, but wildflower meadows do best on poor soil,
so that they don't get swamped by weedy grasses etc, apparently.

See http://tinyurl.com/h4jpncj

and don't ever imagine it's going to be low-maintenance.

Native perennial and bienniel wildflowers such as rushes, docks,
ragwort, thistles, nettles, cocksfoot grass, creeping buttercup will
readily infiltrate the " annual wildflower" area and take over, unless
you laboriously remove the invaders before they set seed.

https://www.rhs.org.uk/advice/profile?PID=446

Janet.