I live in Boston, Massachusetts, USA, and would like to know when to plant my parsnip. I use this site and wanted your answer and opinion on the site's answer. https://www.growmigo.com/
I plant mine in the spring. Takes a bit longer than other seeds sown into the garden soil to see germination but I am just now getting great parsnips and rutabagas...have you tried rutabagas? Wonderful mashed with potatoes and made into fries.
I live in zone 1b. Our winters are tough so anything that needs to be allowed to overwinter has to be started earlier, such as cover crops for barren beds. Garlic just didn't work here but I shall try this fall for next year because we now have a proper heated and skinned greenhouse.
I haven't looked at your site as yet, I am assuming they want you to plant in the fall? Need to know your zone and circumstances. I grew parsnips and rutabagas in zone 3 beneath 11 feet of snow...and they were fine in the spring! Amazing. They did fine where the potatoes did not.
I'll check out the site you sent and let you know if I've any more information.