Try to aim for a seed spacing of at least
3.96 feet (1.22 metres) and sow at a depth of around
0.25 inches (0.64 cm).
By our calculations, you should look at sowing Harextra about 35 days before your last frost date.
As Harextra is hardy, ensure temperatures are mild enough to plant out - wait until after your last frost date to be on the safe side.