Keep in mind when planting that Golden Guardian is thought of as half hardy, so it will need cloching or fleece protection when the temperature dips. Golden Guardian requires a soil ph of 5.6 - 6.5 meaning it does best in weakly acidic soil.
Direct sow after all danger of frost is past.
By our calculations, you should look at sowing Golden Guardian about 49 days before your last frost date.
Ensure that temperatures are mild and all chance of frost has passed before planting out, as Golden Guardian is a half hardy plant.