Hi Caroline, yes you can but you must let the seeds ripen first. Leave the flowering stalk on the plant until the pods turn brown, then cut them off and you can collect the seed by opening the pods. You can sow them straight away if you have a coldframe to overwinter the young plants in, or save them and sow in February in small pots on a windowsill indoors, or March outdoors. Soak the seeds for 24 hours before sowing. Overwintered plants will flower in the summer, but those sown in March may not flower until the next year. The flowers may not look like those on the original plant, especially if that was an F1 hybrid variety.