Chiltern seeds sell the seed and they are a british company. they describe it as hardy. So I suspect it will be fine in the ground. take stem cuttings as a security in case it doesn't survive the winter. then if it does you have more than one plant.

Penstemons are very easy to grow, and I find they are very hardy, I have many and they all come through the winter with no problems, they require no special conditions, the ideal summer plant with a long flowering season.

Thank you SBgirl and Lizzie. Exactly what I needed to know. Now that the torrential rain has stopped I can go out and plant them.