royal is generally regarded as a hardy plant, so this plant will survive close to or on freezing temperatures. royal needs a soil ph of 6.1 to 7.8 (weakly acidic soil - weakly alkaline soil).
Growing royal from seed
By our calculations, you should look at sowing royal about 5 days after your last frost date.
Transplanting royal
royal is hardy, so ensure you wait until all danger of frost has passed in your area before considering planting outside.