I have grown commercial grass seed and wildflower mixes from farm trader type shops, not much variety of flowers came up!
Select a non vigourous grass, not rye grass, and either add packets of wildflower mixes or grow them as plugs and plant later.
The grass seed can go on as soon as you are ready. Remember to firm the soil by doing the silly walk all over it then a quick rake to levell it.
Ivor
