Days to maturity are from date of transplanting, not seeding.
Artichoke seed needs vernalization to trick it into thinking it has already gone through a season of growth. Start indoors in mid-February at warm temperatures (at least 60°) avoiding direct hot sun or overwatering (misting is preferred). Transfer after 6 weeks to a cold frame when outdoor temperatures stay above 25°. Keep as cool as possible over the next 6 weeks without going below 25°. Set out with IRT plastic mulch
and/or row covers
. Feed heavily and give lots of moisture and space (10 sq ft per plant).