Keep in mind when planting that Flat Leaf is thought of as hardy, so this plant will survive close to or on freezing temperatures. Ideally plant in loamy and potting mix soil and try to keep the ph of your soil between the range of 6.0 and 6.0 as Flat Leaf likes to be in weakly acidic soil.
Sow
0.25 inches (0.64 cm) deep with a guideline distance of
7.8 inches (20.0 cm). Soil temperature should be kept higher than
10°C / 50°F to ensure good germination.
By our calculations, you should look at sowing Flat Leaf about 35 days before your last frost date.
Ensure that temperatures are mild and all chance of frost has passed before planting out, as Flat Leaf is a hardy plant.