Dec, Jan, Feb
If the ground is dry enough, winter is a great time for digging - but keep off any soil that is frozen or waterlogged.
Dig a neat trench as deep and as wide as the spade, turning the soil onto the side as you go, breaking up large clods.
Add home-made compost, leaf mould or manure to the trench, or use bags of green waste bought from the council.
Fork compost into the soil, breaking up the base of the trench to improve the drainage beneath.
Work your way down the bed, only walking on un-dug ground. Turn topsoil from each trench into the previous one.