Mulching can be a very labour saving exercise because some mulch can be used to suppress weeds by excluding light from the soil. Not only that, but a mulch can be used to help keep the moisture in and be decorative too. December is not the best time to put down the mulch - even assuming you can see the soil for all the snow we've been having, but mulch laid in the Spring or late Summer when the soil is warm will benefit the roots by insulating them. Mulch is often put round new plants to reduce temperature fluctuations and as the weeds are suppressed there is less competition for the moisture and nutrients that the new plant needs to become established.
Garden compost can be used as a mulch although it is more beneficial to dig it into the soil so that the worms can do their stuff. Garden compost is less efficient as a mulch because it does not suppress weeds so well but it is usually freely available from most average sized gardens with a bin so is worth considering at least for some beds. It is better to shred prunings so that they can be incorporated into the soil more easily to release nutrients back. Leaf mould and pine needles from a separate compost bin however, make excellent mulching materials especially around heathers and rhododendrons where they make a natural looking backdrop. Pine needles also take a long time to decompose so the effect is long lasting. mulch blowing in Spring Green, WI. mulch blowing in Spring Green, WI. They also make for a soft walk way - footfalls are almost silent so a good choice for mazes or a bird hide approach. Leaf mould is great at protecting dormant plants in winter but will blow about a bit when dried out.
Saw dust and wood shavings can be used although they contain fewer nutrients and can even nick the nitrogen from the soil for a time as they decompose. Nitrogen deficiency can affect plants and if that appears to be the case it can be remedied by adding dry poultry manure.
Earthworms are better protected from birds by a thick layer of mulch, although blackbirds and thrushes enjoy digging about in the mulch in search of a meal and will disturb the neat mulched bed given half a chance!
Many mulches are decorative giving contrasting effects of different textures and colours in a knot garden or enhancing a featured plant, or carrying a theme across other parts of the garden. A patchwork border was experimented on in Germany - one half had organic mulch the other had none - the plants with the mulch were seen to benefit.
Well - rotted farmyard manure with a high straw content is good for the fruit garden although cocoa shell mulch will undoubtedly smell better - a waft of chocolate is always preferable! The only drawback to cocoa shells is that it does blow about a bit whereas forest bark is more stable and sweeter smelling than farmyard manure. Gravels can provide a decorative finish particularly around alpine plants where good drainage is required but gravel is not a good idea around moisture loving plants or near a lawn where it can damage the mower blades if it escapes.