Flower-meadows are sown on prepared earth. For this, a regrettable but current procedure involves applying a weed-killer to pre-existing meadows or lawns. I had to fight against the accepted ideas promoted by the lobbies for pesticide products to prove it was possible to create a flower-meadow in soil merely prepared with a rotovator. Even better, if the surface is not too great, you can spread a black tarpaulin or old blankets on the pre-existing grass for six months, to cleanse the soil before working the earth.
The sowing is performed preferably in spring in soil that has warmed up (April-May according to the climate). Then the flower-meadows composed of annuals (poppy, cornflower, ammi (bishop’s flower), corncockle) bloom in the summer. Note that they will not bloom again the following year unless they can be liberally re-sown in earth that has been worked again, as was once the custom with fields of cereals.
You can work the earth every spring with the rotovator to incorporate the seeds of the annuals. Many lovers of flower-meadows are put off by this maintenance work. Therefore, I often advise people to let an existing lawn grow and transform into a magnificent grass meadow, without colourful flowers, but only requiring a mowing at the end of the summer. Moreover, this solution has less of an impact on the ecology.