Posted: 28/10/2017 at 10:03
I'm no expert but I garden on clay and seeded a wildflower meadow 6 or 7 years ago.
If it's a new build I'm guessing the ground is pretty compacted which adds to the problem. Clay needs to be broken up to loosen the texture and get air into it so roots (especially seedlings) can move through it and to help with drainage. So lots of sharp sand and grit but no rich compost as wild flowers don't need it (and some of them will go mad and take over).
If you aerate the grass thoroughly using a proper machine it will take out plugs of g rass, then put sand and grit on about an inch deep and brush it in well.
Yellow rattle fees on grass roots so if you can sow some before the 1st frost that will grow next spring (spring sowings don't work apparently).
Then early next spring get lots of plug plants, grow them on a bit then plant them out, digging out an entire bit of turf and back filling with the poorest soil you can find.
Don't forget to get some different grasses as well as flowers and also a selection of flowers that covers the whole season. You'll be able to get plugs of yellow rattle in spring too.
Good luck - it's so rewarding when you see all the insects and well worth the effort