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 Burpee rose giant cactus about 21 days before your last frost date.
As Burpee rose giant cactus is tender, ensure temperatures are mild enough to plant out - wait until after your last frost date to be on the safe side.