What to do in the garden in December depends on the weather &, more particularly, on how wet the ground is. It is not good to tread on wet soil, because it ruins the soil structure.
In December sow:
- plant winter onion sets if they are not in already
set onion on mark
In December crop or harvest:
- celery
- leeks
- parsnips
- sprouts
- cabbages
- Jerusalem artichokes
- spinach beet
In December protect from cold winds & frost (with fleece or cloches):
- bay
- rosemary
- marjoram
December is a good time to browse catalogues to see what vegetable seeds & plants are on offer, when it is too wet to get on the garden in December.