By David Dickens
University of Georgia
When pine needles start raining down, many Georgians’ thoughts
turn to mulch. But when it comes to mulching flower beds and
under shrubs, pine products aren’t the only choices.
Pine straw and pine bark are among many mulch and landscaping
materials. And they’re plentiful, accounting for 28 percent of
pine trees’ aboveground biomass. (The needles alone are 10
percent.)
Fight erosion, keep water
Mulches can help reduce soil erosion, water loss and weed
growth. Common natural mulches include pine needles, pine bark,
dyed and undyed cypress shavings and other tree species wood
chips and shavings.
Using a mulch around landscape plants can help them survive
and grow. Mulches can keep the top 3 inches of soil cooler in the
summer and warmer in the winter.
Many natural mulches are plant by-products, such as pine,
cypress and hardwood bark, chips and shavings; or recycled
materials, such as mulch pellets made from recycled paper. In the
past, these things were burned or otherwise disposed of.
Black polyethylene and polypropylene sheets are sold as
synthetic materials mulches.
Combinations of synthetic and natural materials are available,
too. Among them are Ecomat (polyester and hemlock needles spun
together), another mat of woven poplar and polypropylene and a
mat of cellulose fiber encapsulated in a nonwoven polypropylene
blanket.
Washed or unwashed stones and pebbles are used in landscaping,
too. But they don’t have the water-holding capacity organic
materials have.
‘Pick a mulch’ checklist
Each of these materials has advantages and disadvantages.
Which is right for you? Does using natural instead of synthetic or
mixes make a difference to you? Any material used as a mulch
should be:
- Aesthetically pleasing. In a recent Auburn University
survey, aesthetic appeal ranked first in importance among
mulch-choice factors. - Porous enough to let water infiltrate but retard evaporative
water loss from under it. The Auburn study ranked soil moisture
retention second. - Hot enough underneath to kill germinating seeds and sprouts.
(The heat comes as fungi and other microorganisms break down
mulches.) - Durable enough to last a long time.
- Nontoxic to plants and animals.
- Unappealing to termites or other unwanted animal and insect
pests. - Effective at controlling erosion.
Consider, too, how much it costs and how often it must be
reapplied. Pine straw must be replenished more often than pine
bark or cypress mulch. Stone lasts the longest.
Hardwood and pine mulches vary greatly in the rate at which
they decay. Generally, though, you can assume a 1-percent decay
rate for wood chips.
Tree bark lasts longer than wood chips, because bark sheds
water rather than holds it. Pine bark and pine needles decay at 15
percent per year for the first two years as a mulch. Pine needles
don’t hold their color as well as pine bark or dyed mulches.
Pine straw vs. others
A study in Louisiana compared pine straw with 35 other
natural, natural-synthetic and synthetic mulches. It had fair
durability and only 7 percent weed growth over the three-year
study. And tests in Georgia found that pine straw had no effect
on surface soil pH after two years.
Deterioration of natural and natural-synthetic mulches isn’t
necessarily bad. Some of the deteriorating fabric/material forms
a fibrous cover over the soil and keeps suppressing weeds after
the mulch appears to be gone.
If you use wood chips or shavings around your home or other
sensitive areas, know where the chips came from. Use only 100-
percent cypress, Eastern red cedar or other termite-resistant
woods.
Don’t use fresh wood chips, which smell sour or vinegary. They
can kill plants. Instead, spread the wood chips out in a thin
layer and wait until the sour smell goes away, then use them. The
best places to use wood chips are in perennial beds and on garden
paths well away from your home.
( David Dickens is an associate professor and extension forest
production specialist with the University of Georgia Warnell
School of Forest Resources.)
