Last year we sowed (?) Marian swedes late in the season, dumped half a packet along an 11ft row having created a shallow furrow. Our plot is on an exposed south coast site on heavy clay. We left it quite late to thin out and tried transplanting a few to fill gaps (nb, the transplants were rubbish, just compost them!) And we ended up with 10 big swedes by Christmas. Some had split a bit, probably owing to irregular watering during the hot weather, and the leaves were decimated by whitefly because we didnt cover them but it didnt seem to affect the root growth at all. We broke off any dead foliage and picked any weeds growing around them.
Made awesome swede mash but in the main we just cut them into batons and ate them raw, dipped in hummous as a snack. The one left in the ground, by the end of the year grew to 6" across and still tasted as good.
This year we're trying Lomond, similar to Marian but is meant to have an even better flavour, if these don't do as well we'll probably go back to Marian and make them one of our plot staples.