Leeks can be slow to germinate, and may germinate more sporadically / unevenly.
Try to aim for a seed spacing of at least 0.39 inches (1.0 cm) and sow at a depth of around 0.78 inches (2.0 cm). Soil temperature should be kept higher than 16°C / 61°F to ensure good germination.Primor F1, French baby