Super Absorbents Save Time and Money
Barbara W. Ellis
Reprinted from American Horticulturist Vol. 61 No. 3
Super absorbents are a new group of wonder products that deserve the attention of gardeners and horticulturists in all parts of the country. These starch-based absorbents are capable of storing several times their weight in water as a gel, holding it available for plants and at the same time actually increasing soil aeration and improving drainage. Their gardening applications, both indoors and out, are many - use them to store water at the root zone of newly planted sod, use them in a seed bed where they will hold a layer of water next to the emerging seedlings, use them to improve the water holding capacity of sandy soils, or mix them into potting soil and use them to store large quantities of available water for container-grown plants both indoors and out.
These sponge-like compounds originally were developed by the U.S.D.A. Northern Regional Research Center in Peoria, Illinois, and, although they are now available in slightly different formulations under several different brand names, all actually are composed of a man-made acrylic compound chemically grafted to cereal grain starches. These powders, which in their dry form may look something like slightly off-color dry milk or wheat germ depending on the product involved, can absorb from 200 to 5,300 times their own weight in water.
I enjoyed experimenting with several different samples I received and compared their amazing absorbency levels. If you purchase one or more of the products in the source list at the end of this article, just for fun place one level teaspoon in two ounces of water. Some of the gels I tested absorbed the two ounces of water, some almost twice as much.
Water held as a gel by these compounds is fully available to plants and will remain in the soil until it is extracted by plants or until it evaporates. The gels will re-absorb water whenever it is available, thus creating a sort of shrink-swell cycle. These super absorbents will last through many such cycles, and in a growing environment they will remain effective for a period of anywhere from six months to several years. They will gradually biodegrade in relation to the number of times they expand and contract.
Most important, these absorbents are able to store water without water-logging the soil. As the particles of absorbent expand they force the soil particles apart, increasing aeration and improving drainage. Once the absorbents are fully saturated, any excess water will flow over and around them just as it would a saturated sponge. For gardeners this means that not only is the danger of root rot minimized, but also the lack of water stress imposed on plants and improved aeration actually help to speed plant growth.
These water absorbent polymers are compatible with all species of plants. They do not affect and are not affected by the pH of the soil or soiless growing medium, and, in their dry form, they can be stored indefinitely in a moisture proof container.
Obviously, a product with all of these characteristics could be put to an almost limitless number of uses in the garden. In the following paragraphs I will briefly discuss some of the ways they can be used.
Super absorbents can be added to potting soil that is to be used for house plants, container-grown annuals and perennials in the garden, bedding plants and nursery stock. After a thorough initial drenching, plants grown in treated soil will require much less frequent watering. That means container-grown vegetables, which often must be drenched more than once on a hot summer day, will need water much less often. Bedding plants sitting in tiny containers on a hot, sunny window-sill or, worse yet, on a hot sidewalk in front of a supermarket can be watered less often without subjecting them to water stress. Difficult-to-water hanging baskets will be much easier to care for.
Interior plantscapers are using super absorbent-amended soil mixes to reduce their watering schedules on indoor plantings, and with a little bit of experimentation, a vacationing house plant enthusiast or patio gardener could have his vacation and still keep his peace of mind knowing his plants are all well watered. Indoors, plants grown in amended soil may need water as seldom as once a month, and wick watered plants or those grown in self watering planters will need water even less often. Either repot house plants with amended soil or mix some super absorbent with water to form a loose gel and plant plugs of it directly in the pot. Plant roots are able to extract water directly from the gel, and rooted cuttings actually can be kept in super absorbent gel alone. The roots act as a check valve and allow water to enter the root but not leave it. Do not try to root cuttings in this manner, however, since, in the absence of roots, the gel can pull water out of the plants. You can grow un-rooted cuttings in a soil amended with super absorbent.
Watering schedules will take some experimentation and will vary according to the size and type of the container as well as the plants involved. Absorbent Industries (see the source list at the end of this article for the address) has a special formulation of super absorbent designed for indoor use, AquaStor 450, now called AquaStor 600se. Mix it at a rate of one teaspoon per quart of growing medium or five pounds per cubic yard. Super absorbents can be added to soil along with fertilizer and any other soil amendments you wish to add, and the soil can be steam sterilized.
Outdoors use a formulation designed for nursery or landscape use (for example AquaStor 900, now called AquaStor 1000) and apply it according to the package directions. When transplanting vegetable sets or bedding plants grown in amended soil, plant any excess growing medium along with the transplants, because the absorbents will continue to store water for plants in the garden. The treated soil will help to lessen transplant shock since it will keep a supply of readily available water near the young plants.
Seeds and Seedlings
To improve the germination percentage of seed and the performance and strength of seedlings add super absorbent to the germinating medium, or work a small amount of the powder into the seed bed before planting (consult the package for the proper amount). These absorbents even can be broadcast over the ground and then worked into the surface of the soil when seeding a lawn. Moisten them thoroughly, and they will hold a layer of water next to the seeds, which will be available to the seedlings as soon as the root tips emerge. Agriculturists actually are experimenting with encasing different types of crop seed in a pellet of super absorbent either by itself or in combination with fungicide, fertilizer or other ingredients. Coated seed has been proved to out perform un-coated seed in a number of different field trials. Perhaps eventually some flower or vegetable seed for the home gardener will come pre-coated with a super absorbent.
Landscape contractors have found that super absorbents will act as a binder when mixed with seed, mulch and water, holding the seed in contact with the mulch and water. Seed sown in this manner exhibit higher germination and survival rates. The technique, called hydrolic mulching, even has been effective on slopes where erosion is a problem, since the seedlings get a faster, stronger start.
Super absorbents can be used in a variety of ways to help lessen transplant shock and improve the strength and performance of many kinds of transplants, including large trees, balled and burlapped or container-grown nursery stock, bare root trees, seedlings, shrubs and sod.
When preparing the hole for a container-grown or balled and burlapped tree or shrub work some super absorbent into the hole along with the bone meal and any other soil amendments you are planning to add. Once the tree or shrub is planted and thoroughly watered the absorbent will hold a supply of water right at the root zone for the newly transplanted plant. One of the important characteristics of these new absorbents, especially in this case, is that they trap gravitational water, which is the water that ordinarily runs right through the large pores in the soil and is lost. As a result, water that would be lost is trapped in the root zone, and water waste due to run off is greatly reduced. Be sure to work the absorbent into the soil. If you merely line the hole with the powder, it might create a gel-like ball around the plant and thus reduce aeration.
Bare-root plants can be dipped in a thin slurry of super absorbent and water to reduce transplant shock and improve performance. This treatment also can be used to store water on plant roots during shipping, where it will reduce damage caused by drying out and will weigh less than ordinary growing medium. Even seedlings being transplanted will benefit from a dipping, since it will help prevent their tender roots from drying out during and after transplanting. Make sure the mixture is thin enough so that you can dip the roots into it without damaging them, and that it clings to the roots without completely covering them.
These are only a few of the many uses for super absorbents, and scientists, horticulturists, landscape contractors and home gardeners undoubtedly will discover more as these products become better known.
Super Absorbents are available under several different brand names, including AquaStor™, Terra-Sorb®, Super Slurper, Viterra 2 and Permasorb. Thus far, most of these products are available only to nurserymen and other professionals, but homeowners can purchase both formulations of AquaStor from Absorbent Industries, Inc., 611 Jefferson Street, Morton, IL 61550. Some of the super absorbents also may be available at local nurseries and garden centers, and plans are underway to market Terra-Sorb® through these retail markets in the future.