American Annual meadows includes Cosmos Seed
In principle these are similar to sowing standard cornfield annual mixes.
Annuals will not establish very well amongst grass or other vegetation. They need to be sown on ideally weed free soil.
These mixes should be broadcast at a rate of 3 grams per square metre. Sow from end of August through to Early October. Or in March/April. After broadcasting roll or consolidate the soil. The aim is to push the seed into the ground rather than bury it to deeply.
Autumn sown annual mixes should produce a mass of flowers from June onwards,
It may be possible to re-establish the mixtures after the seed has shed in the autumn by surface cultivation and rolling in the autumn.