Aim to sow
5.85 inches (15.0 cm) deep and try to ensure a gap of at least
11.7 inches (30.0 cm).
By our calculations, you should look at sowing Maris Piper about 14 days before your last frost date.
Maris Piper is tender, so ensure you wait until all danger of frost has passed in your area before considering planting outside.