When To Do It Mulch all new plantings at planting time. Existing trees may be mulched any time chips are available. How To Do It Wood chip mulch is easily applied with regular garden tools. Simply put down 3-4 inches of chips, level off and tamp lightly, pulling chips away from trunk slightly. There is no need to use plastic sheets with rocks.
Rocks hold heat and can be detrimental to plant health.
Planting a New Tree or Shrub For best results, strip away all sod to a depth of 2-3 inches and to the diameter you plan on covering with wood chips. The wider the hole and the larger the mulched diameter, the better. For additional weed control, a porous landscape fabric which allows for air and water exchange may be put down before the chip mulch. Mulching Older, Existing Trees DO NOT strip away sod. Simply lay down 4 inches of chips from the trunk out a foot or two past the present drip-line.