I would start the seeds indoors late February and transplant outdoors when threat of frost is past - late April.

Hi, if you want to sow the seeds outside, sow them just below the soil surface, about 1-2 weeks before the last expected frost, usually about mid may in the U K, they should germinate in 10 - 14 days, when they're large enough to handle, thin them out to 18 -36" apart, they like a rich, moist soil, in full sun, although they are perennial, they are a short lived perennial, and never flower as well in subsequent years, as they do in the first year, so they're better grown as an annual, from seed each year, Derek.

Thank you😉