Keep in mind when planting that Sorbet 'Purple Duet is thought of as hardy, so this plant will survive close to or on freezing temperatures.
By our calculations, you should look at sowing Sorbet 'Purple Duet about 90 days before your last frost date.
Ensure that temperatures are mild and all chance of frost has passed before planting out, as Sorbet 'Purple Duet is a hardy plant.