Try to aim for a seed spacing of at least
11.7 inches (30.0 cm) and sow at a depth of around
0.25 inches (0.64 cm).
By our calculations, you should look at sowing Dahlia Flowered Mixed Colors about 21 days before your last frost date.
As Dahlia Flowered Mixed Colors is tender, ensure temperatures are mild enough to plant out - wait until after your last frost date to be on the safe side.