They go by various
names‹ superabsorber, hydrogel, water-absorbing crystal. Technically,
they're synthetic, cross-linked polymers that are widely used
now forestry, gardening, and landscaping as a means of conserving
water. When dry, they resemble coarse salt crystals, but they
will absorb many times their weight in water, swelling into gelatinous
globs that gradually release their moisture as the soil around
them dries. Besides conserving water and a gardener's time, they
reduce leaching of fertilizers and nutrients into ground water,
a major benefit to the environment.
In the old days before
superabsorbers, peat moss was the soil additive of choice to hold
water, to the point where the demand was destroying the world's
peat bogs. What gardener could have imagined that someday we'd
have a product that could store water in the soil and then release
it as the plant's roots need it?
There are many brandnames:
Broadleaf P4, Soil Moist, Moisture Mizer, TerraSorb, Hydrosource,
Watersave, Water Crystals, etc. Most recently there are potting
mixes with moisture-holding polymer already blended into the mix
such as Smart Soil and Moist Soil. (But save your money by buying
regular potting soil and adding polymer.) These magic crystals
are also used hats, bandannas, and headbands to absorb perspiration.
Uses for superabsorbers
are many: as a soil amendment for container planters; in seed
germination; as a dip for bareroot plants; as a transplant aid
for turf, bedding plants and woody ornamentals; and as an in-soil
water storage medium for turf. Horticulturists often recommend
adding hydrogels to container plants, especially hanging baskets
and window boxes. And testimonials from gardeners on the Internet
abound.
Apparently there are
two types of absorbent polymers in the trade. Both are synthetic
polymers, either polyacrylamides or polyacrylates.
Polyacrylate is the
active material in baby diapers This superabsorber is capable
of absorbing 400-800 times amounts its mass, but rapidly breaks
down. Polyacrylamide is the gardener's friend. It was developed
in the 60's to grow plants in arid environments. Since then, it
has been refined to last longer and absorb water at higher rates.
It's estimated that one pound of crystals will absorb and hold
from 15 to 40 gallons of water in the soil.
Polyacrylamide works
in the soil for several years and then breaks down to carbon dioxide,
water, nitrate and lactic acid, according to the Hydrosource Web
site (http://www.conserving-water.com/docs/hydrosource.html).
Another report says the crystals break down into water, carbon
dioxide, and ammonia.
Long-term safety is
an important question, but little has surfaced during the 30-plus
years since the original development of the polymer that would
give any special cause for environmental concern. Now that it's
in widespread use, you can bet they're re-verifying its safety.
One report indicated that superabsorbers are used in organic farming.
In any case, care should be used not to inhale airborne particles
of the powdered form. Use good sanitation practices (wash hands
after use) and store away from children, food, and animals.
The lifespan of the
product varies depending on which manufacturer's Web site you're
reading. Sometimes the claims are vague, saying the product "will
last for years." Water Crystals promises 12 or more years; Hydrosource,
12 to 15 years. My guess is that it's highly variable, depending
on soil, hydration cycles, climate, etc.
Superabsorbers are
unscathed by normal pH's encountered in soils, composts, and irrigation
water. At pH levels of less the 5, however, the water absorbency
is reduced. Also, the crystals in some cases may increase the
effectiveness of the herbicide and fertilizers. So go easy on
both. Salt content of soil and water represents one of the few
potential threats to the crystals' longevity and may limit its
usefulness near the coast. UV light will degrade hydrated crystals
sitting on the surface of the ground, so keep the product buried
in soil or mulch.
These products are
manufactured as powder, dry granules of different sizes, or hydrated
as a slurry. You can use the dry crystals right out of the package
or hydrate them overnight. Even distribution of crystals in the
soil is important as you don't want to create wet pockets. If
you use the product dry, apply extra water for a few days until
it's certain the product is hydrated. Dry crystals can actually
take moisture from the plant until they are hydrated.
Lowes and Home Depot
carry superabsorbers, and it's easy to buy them online. Fortunately
the price is coming down. One pound of polymer crystals costs
less than $20. Watersorb.com charges $15 plus shipping for a two-pound
package, the smallest size it offers on its Web site.
While none of these
products is cheap, note that it only takes a tiny bit to do the
job. For instance, Watersorb recommends that you need 3 teaspoons
for a 10-inch pot. Using more isn't better, and can turn plants
into soup very quickly. Also, constantly wet areas may invite
algae. In climates like Southwest Florida where I live, crystals
are a godsend in the dry season but, once the rains arrive, could
drown plants by holding in the moisture. High humidity is likely
to be a factor as well.
For existing plants,
you can make holes in the soil with a pencil and pour prepared
product in them. On in-ground plants, spread a thin layer of the
hydrated product under the mulch to avoid UV exposure.
An in-depth discussion
of how to use superabsorbers can be found at the FS
Stores in Ontario Web site*. The site covers how to use superabsorbers
with bare-root plantings, new sod or seed turf, houseplants, repotted
plants, tree and shrubs, existing plants, flowering plants, and
vegetables. Expect to experiment as the needs of soils and plants
will vary. Whatever you do, read the label and follow the manufacturer's
directions.
*(http://www.fsstores.com/growers/techniques/crystals.shtm)
