Landscape, Nursery, Turf, and Greenhouse - Water Absorbing Polymers II

The following is more information on water absorbing polymer use in horticultural applications during establishment.

Hydrogels have been used in field establishment of revegetation projects, as well as perennial, and annual establishment and production. Plants installed in media with hydrogels have had different responses. For instance, plants requiring more moisture than is readily available seem to benefit from hydrogel additions, but negative responses can occur if the hydrogels are used in environments that are naturally moist and xeriphytic plants are planted. Plants also have unique responses for different growth stages, so amounts of hydrogel required may vary as a plant develops.

Research on plant establishment in dry conditions has shown benefits for using these hydrogels (water absorbing polymers). Pinus halepensis (Aleppo pine) doubled its survival rates in 0.4% hydrogel soil compared to no hydrogel amendments. The hydrogel also prolonged water availability for plant use when irrigation was stopped. The hydrogel media also allowed for 19 days to pass before plants started to die whereas in the control with no hydrogel plants started to die after five days of drought. Pinus pinea (umbrella pine or Italian stone pine) seedlings survived 1.4 to 2.0 times longer with applications of hydrogels compared to the trials with no hydrogels in the field production. Pinus halepensis also had increased adventicous root growth along with increased overall plant mass when the hydrogel was added to the media. Research has shown that Quercus rubra (red oak) and Nyssa sylvatica (black gum) had increased root regeneration when rooting hormones were added to the polymers for transplant aids. Dehgan and others (1994) noted that foliage plants like Photinia x fraseri (Fraser photinia) responded in increased mass to the incorporation of hydrogels into media.

Hydrogels usually have some effect on plant establishment, with the greatest benefit for moisture loving plants planted in dryer conditions. Festuca arundinacea ‘Rebel’ (Tall fescue) benefited from pre-seeding incorporation of hydrophilic polymers into the soil. Pyracantha cocinnea (scarlet firehorn) and Rhododendron sp. (azalea) had increased survival and increased dry weights in container production when a hydrogel was incorporated into the media. Drought sensitive annuals, such as Petunia parviflora (petunia), responded well to hydrogels in dry conditions and increased flower numbers and dry weights.

Not all plants respond the same to hydrogels. One issue is that thay retain fertilizer salts. This can actually reduce plant growth. In container production of Betula pendula (European birch), hydrogel incorporation into the media has shown a reduction in overall plant mass and also decreased the amount of water available to the plants. After further investigation, the lack of water availability was attributed to the amounts of soluble salts in the media. Another research project found that Codiaeum variegatum (croton), Dieffenbachia sp. (dumb cane) and Hibiscus rosa-sinensis (hibiscus) showed no visible size differences when hydrogels were used compared to not being used. Annuals requiring dry regimes such as Catharanthus roseus (vinca) do not respond well to extra water being held by the soil.

Extracted from "Hydrophilic Polymers – Effects and Uses in the Landscape" by Daniel Peterson in the Restoration and Reclamation Review Student On-Line Journal, University of Minnesota, St. Paul, Minnesota (USA), Department of Horticultural Science

Landscape, Nursery, Turf, and Greenhouse - Water Absorbing Polymers

I recently had a converstion with an owner of a lawn maintenance company. He mentioned that another company was having success with water absorbing polymers injected into turf. I thought I would do a series on water absorbing polymers and their use in horticulture. The first post is general information on what these polymers are and their use.

Water absorbing hydrogel polymers have the potential to have a large number of benefits on the landscape. They have proven to be an aid in decreasing erosion, thus reducing nutrient and sediment losses to sensitive environments, and adsorb nutrients for slow release. Hydrogels have also, in most circumstances, aided in the establishment of plants, mycorrhizae, and bacteria. However, the most important aspect concerning hydrogels is that responses associated with them are site-specific variables (i.e. soil structure, salt and fertilizer concentration) and often species-specific variables (i.e. what conditions the plant normally grows). Given the adverse side effects potentially associated with the hydrophilic polymers, care should be taken in determining what the ultimate objectives of the project are (i.e. temporary plant establishment or permanent, irrigated or unirrigated, etc.). Therefore each field use must be carefully analyzed for organism responses expected due to the wide range of results possible when using these products.

Hydrogel polymers used in horticulture are usually formulations commonly made of starch-polyacrylonitrile graft co-polymers (starch co-polymers: SCP), vinyl alcohol-acrylic acid co-polymers (polyvinylalcohols: PVA), and acrylamide sodium acrylate co-polymers (cross-linked polyacrylamides: PAM). All of these hydrogels when used correctly and in ideal situations will have at least 95% of their stored water available for plant absorption. Natural polymers (i.e. starch based SCP) are very fast hydrators and will usually completely hydrate in as little as two hours where as the synthetic polymers (i.e. PVA or PAM) can take six hours or more to fully hydrate. Usually synthetic polymers like PAM are used over natural polymers since they tend do last longer in the soil matrix because they are less biodegradable.

Information reprinted from "Hydrophilic Polymers – Effects and Uses in the Landscape" by Daniel Peterson in the Restoration and Reclamation Review Student On-Line Journal, University of Minnesota, St. Paul, Minnesota (USA), Department of Horticultural Science
URL: http://hort.agri.umn.edu/h5015/rrr.htm