For instance to quote from the National Allotment Society
“Dig up rhubarb roots and divide them leaving the sections on the surface of the soil for a few days to let them be frosted prior to forcing. Cover any crowns in the soil that have been set aside for forcing with an upturned bucket or flower pot and cover the drainage holes to shut out the light. With luck you will be harvesting pale pink sticks by late February.
Check on any fruit and vegetables in store and remove any that are diseased or soft.
Towards the end of the month when the weather and soil conditions allow plant out soft fruit bushes. Spray all fruit trees and bushes with a garlic winter wash on a fine day; do not spray in frosty conditions. It won’t hurt to hold the job over to next month.”
There is a different set of observations here at the Allotment.org website – such things as checking on the glass in greenhouses. Winter winds do damage.
Some people are starting their onions from seed, tomatoes plants from seed and also aubergine plants in January. Many a gardening house with no heated greenhouse will have window ledges full of tomato and aubergine seedlings very soon. Light is the trick here.
But with most things – patience is a great virtue. Mind you, getting in early with the seed potatoes so that you get the variety you want is good advice.
Of course all your vegetable peelings will be going on the compost heap – or if the weather allows a fork in the soil, a bean trench can be started.