Keep in mind when planting that Sonnet pink is thought of as very hardy, so this plant will tend to survive through freezing conditions. Sonnet pink needs a loamy soil with a ph of 6.0 to 7.0 (weakly acidic soil to neutral soil).
By our calculations, you should look at sowing Sonnet pink about 56 days before your last frost date.
Ensure that temperatures are mild and all chance of frost has passed before planting out, as Sonnet pink is a very hardy plant.