Keep in mind when planting that Rembrandt is thought of as very hardy, so this plant will tend to survive through freezing conditions. Ideally plant in loamy soil and try to keep the ph of your soil between the range of 6.0 and 7.0 as Rembrandt likes to be in weakly acidic soil to neutral soil.
By our calculations, you should look at sowing Rembrandt about 56 days before your last frost date.
Ensure that temperatures are mild and all chance of frost has passed before planting out, as Rembrandt is a very hardy plant.