Jute Mulch Mats
Organic Mulch Fabric for Single Trees
These squares of jute mulching fabric, made from 1000g per square metre material are strongly recommended for use with standard trees (the largest delivery size of tree). They suppress weeds and retain moisture - weeds and dry soil being the 2 main killers of newly planted shrubs and trees. The mats are slitted to fit around the trunk of a newly planted tree and rot down naturally after about 2 years, improving the soil as they go.
You can buy plastic pegs to pin them down - you can also make your own or use metal camping pegs. Or just push the corners of the mat into the soil with a spade, but using stones to hold the mulch down is not ideal as they will create dry patches in the soil underneath them.
You can also buy lengths of polypropylene mulch fabric for hedges.