well yes and NO, cold will slow things down, on about all plants
BUT many time planting brassicia type seeds, turnips, rape what ever, its always a GOOD idea to go back and add urea about 3-4 weeks after you plant, it gives them a boost, and helps them fill in better(most seed companys actually recommend this as well)
the best time to do so is just before a rain too, as urea will just go up in the air it seems, and the plants won't get as much from it

I typically go about 60-100 lbs an acre, pending how i fertilized the site prior to planting, over the yrs i found on brassicia type plants I go a little extra on the nitrogen level at seeding. they seem to get a better take doing so, I'll add an extra 20 % or so

your a little south of me, and my one plot is doing much better than the other, seems this yr with the dry spells then wet spells, the shadier field is doing much better for me too
so, till we get a frost, it will keep growing