Keep in mind when planting that Princessa Rio de Plata is thought of as tender, so remember to wait until your soil is warm and the night time temperature is well above freezing before moving outside.
By our calculations, you should look at sowing Princessa Rio de Plata about 91 days before your last frost date.
Ensure that temperatures are mild and all chance of frost has passed before planting out, as Princessa Rio de Plata is a tender plant.