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