"Mulch" is anything with which you blanket theground, be it straw, black plastic, pebbles, even the marbles I once saw blanketing aportion of ground in a contemporary California landscape. Any of these materials, when spreadbeneath a tree or shrub, will keep lawn and, hence, lawnmowers at bay. Mulches also helpconserve water by slowing evaporation from the soil surface.But that's about where the similarity among mulches ends.
Many mulches can enhancewater use, for instance, by softening the impact of raindrops, so the soil surface stays loose, openand ready to absorb water. Rule out black plastic for this purpose, however. Anotherdownside to black plastic is that it can leave roots gasping for oxygen.
MORE BENEFITS OF MULCHMulches can contribute directly to a tree or shrub's nutrition and health. As any organicmaterial (wood chips, straw or leaves) decomposes, it releases nutrientsand also helps make plant foodstuffs already in the soil more accessible to roots. Ruleout pebbles, marbles or black plastic for this.
As far as a tree or shrub is concerned, organic materials are obviously the best mulch.
And besides their benefits for plants and the soil, they are usually inexpensive orfree.
Still, mulching even with an organic material can be one of the worst things you do foryour tree or shrubs.
POSSIBLE DARK SIDESPotential Problem No. 1 is that mice simply love thecushiony, moist environment created by organic mulches. Furthermore, mice like to gnaw on the bark of livingtrees and shrubs, so a thick mulch piled up against woody plant stems provides these furrycreatures with both food and lodging.
Since plants transport minerals and sugars through the bark, mousefeeding can kill a tree or shrub.An obvious route around this mouse problem is to keep organic mulches away from thebases of plants. A ring of bare soil a few inches in diameter around the base of a tree orshrub is sufficient to cause Stuart Little to think twice about scurrying out, exposed to thesearching eyes of hawks and other predators, for a bite to eat. A cylinder of hardware cloththere provides further insurance.Potential Problem No. 2 with using an organic mulch is that it can bring on rot if piled up against trunks and stems. Again, bypass this problem by keeping the mulch a few inchesaway from trunks and stems.
AESTHETICSOne last quality of mulches is their contribution to theappearance of a landscape or planting. Again, rule out black plastic for this purpose.
True, plastic can be covered with something like wood chips, but coverings eventually slide off toexpose the plastic.
Other mulches each have a place in helping tocomplete a picture: wood chips or leaves in a woodland setting, cocoa bean hulls informal shrubbery, marbles in ... where?