More muck, this time at the South London Botanical Institute. They had a couple of tonne bags of compost delivered- one of well rotted horse manure, the other of spent mushroom compost. Mulching can be done any time of year but it's a task best suited to winter when plants are dormant- keeps you warm too!

 A couple of caveats where mulching is concerned. Animal dung should always be very well rotted, too fresh and it can scorch plants. Mushroom compost is somewhat alkaline and shouldn't be used around ericaceous plants or overused to the extent it alters the soil PH.

 One major concern about any compost from an external source -including 'green waste'- is that it's generally impossible to know what chemical residues it may contain unless from a certified organic source. For example there have been well documented issues with contaminated manure from animals grazed on grass treated with herbicide. 

 It show just how powerful these herbicides must be that they can be sprayed, pass through an animal's digestive system, composted, bagged and stored but still be potent enough to damage plants when used in gardens and allotments. Probably the only compost you can be completely sure of is the home-made variety.