I find that as Autumn progresses that the foliage starts to get straggly & I tidy them away to prevent slugs hid8ng in there but I leave the parsnips in the ground to continue their growth & get frosted, I sometimes get a few up if bad weather is forecast as a couple of years I’ve been caught out by very heavy frosts & not been able to get any up for Christmas dinner, shock horror, & had to resort to buying some. Some on our allotments dig tgem all up late October/November & freeze them just so they can clear their plots. I suppose it doesn’t do for us all to be the same 😂