NO HAGGIS feast would be the same without 'neeps and tatties', which may prompt you to try to grow some in the new year.
Maincrop varieties are the easiest to grow and can be sown in July and August, for a first crop from October. Good varieties include 'Manchester Market', which is recommended for long storage, 'Golden Ball' and 'Champion Green-top Yellow'.
Turnips do well in non-acid soil with reasonable drainage. Sow them thinly in a non-shady spot and thin them out as soon as the seeds are big enough to handle, until the plants are 25cm apart. Water them regularly to make sure you don't end up with small and woody roots and hoe regularly to keep weeds under control.
Start lifting them as soon as they are large enough to use, as they deteriorate with age. However, in most areas you can leave them in the ground and lift them when you want them.