Keep in mind when planting that Blackjack is thought of as half hardy, so remember to protect this plant from frosts and low temperatures.
Try to aim for a seed spacing of at least
8.97 inches (23.0 cm) and sow at a depth of around
0.0 inches (0.0 cm). Soil temperature should be kept higher than
18°C / 64°F to ensure good germination.
By our calculations, you should look at sowing Blackjack about 90 days before your last frost date.
Ensure that temperatures are mild and all chance of frost has passed before planting out, as Blackjack is a half hardy plant.