To create greater uniformity and
consistency, single shredded bark mulch is put through a tub grinder to create "double
shredded bark" and sometimes ground a third time for "triple shredded
bark." Some sawmills also add ground wood or sawdust to the mix.
shredded bark remains in a stockpile, the darker it becomes. If bark remains in a
stockpile too long, anaerobic conditions within the pile can allow toxins to build up.
This mulch will have an "ammonia smell" and should be spread
out on a paved
surface (Caution: concrete surfaces may stain) to air-out prior to being used in the landscape.
If used too soon,
without time for airing-out, the fumes
from this mulch will kill annual flowers as well as burn shrub
foliage and bordering turfgrass.
Some people feel that watering this mulch with a garden hose right after it's spread will reduce the
chances of plant damage by "knocking down" the toxic fumes. But it
is best not to buy shredded bark that you suspect is "killer bark" in
the first place... because as the old saying goes, "an ounce of
prevention is worth a pound of cure."
Wood mulches remove nitrogen from the soil
when they break down, so it is advisable to fertilize your shrub beds
around the same time you mulch them.
Slow-release nitrogen is
safer to use than quick release nitrogen. Organic sources of nitrogen
are the safest of all with the least potential to "burn" plants, but
they are more expensive to use.