Keep in mind when planting that Jumbo Jet is thought of as tender, so it is really important to ensure that the outside temperature is well above freezing before planting or moving outdoors.
By our calculations, you should look at sowing Jumbo Jet about 91 days before your last frost date.
Ensure that temperatures are mild and all chance of frost has passed before planting out, as Jumbo Jet is a tender plant.