What is Hydroseeding? From Industry Experts

Hydroseeding is a hydraulic planting method in which a slurry mix of water and seed is sprayed onto a planting surface for revegetation purposes. There is quite a range of different seeding techniques and hydroseeding is one of them. Generally, seeding rates are determined by the method of seeding, selected plant species (often but not always grass) and purity of the seed. In cases where there are seed mixes, their development should be based on pure live seed to account for species that have low germination rates or mixes that would otherwise have a high amount of inert material, including dirt or other plant parts. Local jurisdictions and expert recommendations from revegetation specialists helps in determining the pounds of seed per acre, determine the amount of seeds per square foot desired and the amount of seeds per pound of each species selected. Timing of seeding is very important to the revegetation process with most favorable times in non-irrigated areas being in autumn, to allow for seeds to take advantage of winter and spring moisture (region dependent). Seed should not be applied if the soil is frozen, snow-covered or wet as proper is seeding time is dependent on adequate moisture and soil temperatures for germination and seedling growth. The evaluation of hydroseeding, where it is utilized and how Global Road Technology offers innovative solutions related to hydroseeding will be discussed in this article. 

What goes into a hydroseeding mix?

Hydroseeding can simply be a slurry mix of water and seed, however commercially applied solutions often also incorporate fertilizer, fibres, a binder/tackifier, and other additives such as mycorrhizal fungi that is sprayed onto the surface of an area to be seeded. Soil binders in hydroseeding are added to a slurry to give temporary soil cohesion, holding the seed and surface soil particles in place on steep slopes helping to ensure even cover establishment. Soluble fertilizers are utilized, which once dissolved the nutrients become readily available to the germinating species which offsets any loss of seed germination and plant vitality in higher concentration areas of the slurries. It is mixed in a tank-mounted truck and is applied from the truck through long hoses or water cannons. On steep slopes, a tackifier which is a chemical compound that helps the material adhere to the slope is often used. The misconception in interchangeable use of the word hydroseeding with hydromulching should be cleared now as hydromulching does not necessarily contain seed. The wood fibre mulch portion of the slurry is usually dyed to show which areas have been seeded and hydroseeding provides for a single application of all additives, including seeds and mulch for erosion prevention on steep slopes. Scholars and practitioners recommend that hydroseeding must not be utilized unless the slope is too steep to safely walk on because it provides less soil to seed contact compared to other methods. Option could be used in flatter areas when the area is raked following hydroseeding and the best results are achieved through soil preparation, application of the seed and water slurry and mulching. Procedurally, the hydroseeder should constantly be agitated so that the seed and water mixture are consistent and where site conditions permit, the seed should be raked into the soil. 

Other schools of thought consider hydroseeding as more of a hydraulic planting method which is used to efficiently establish large-scale vegetation involving a water carrier for the application of seed under pressure. The basic hydroseeding technique simply sprays the seed-water mixture onto a prepared planting surface. Specialized equipment in the form of a hydroseeder is used to achieve hydroseeding operations and it consists of a large capacity sprayer attached to a large, single-nozzle delivery system with basic parts such as a pump, hose, nozzle and a tank fitted with paddle or liquid type agitators to provide continuous mixing of the slurry.

Where is hydroseeding best suited?

Applications of hydroseeding is well adapted for re-vegetation of huge tracks of land, as well as for poor or barren land of sand or rock and generally for steep, denuded slopes which are often difficult to revegetate. In the past, seeds of commercially available fast-growing grasses and legumes were traditionally used as planting materials for hydroseeding but with the growing interest in the use of native plants for re-vegetation, research and development of native seed mixes for hydroseeding have grown remarkably. Seed characteristics such as viability and dormancy are key factors to consider when hydroplanting native seeds. Seed germination test is essential for determining the percentage of viable seeds that have the potential to germinate under favorable conditions which feeds into informed optimum seeding rates whereas seed dormancy mechanisms of specific species gives background information for developing preconditioning treatments to promote uniform germinations.

Understanding the benefits and challenges

Hydroseeding is often used in an attempt to reduce erosion and create microclimates by altering the amount of evapotranspiration and soil moisture availability. The use of hydroseeding in semi-arid and disturbed environments has produced conflicting results with some stating that hydroseeding with native species resulted in poor seedling establishment and others successfully revegetating with native species. The components of the hydroseed mixture may mimic the effects of small amounts of litter have on microclimates and increase soil nutrient availability. The low amounts of litter provided by hydroseeding may improve seedling growth when competitors are present, which may have an indirect positive effect on seedling emergence or growth. Some descriptions of hydroseeding mention dispensing of seeds by using emulsification of water and mulch sprayed out evenly on the surface of the ground, with the perceived advantage of hydroseeding considered as the mulch layer which helps retain moisture and limits soil erosion on the site in addition to being non-labor intensive. The big challenge of hydroseeding is the logistics of having water available in close proximity to the planting sites and difficulty in accurate calibration of application rates. 

Choosing seed blends and applications

Species performance at the germination stage determines the success of hydroseeding with evidence showing that species are able to germinate earlier and at high germination rates more successfully than species with low germination rates especially during periods of low water availability. Although this is the case, other proponents against suggest that the success of native seed mixtures focuses more on plant establishment and less of germination. Global Road Technology offers GRT Nature Plus a spray over liquid polymer that provides erosion control and nutrients to increase germination and strike rate for the short and long term hence can be effectively utilized as a key solution for preventing erosion while seeds establish. 

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REFERENCES 

• Baethke et al. 2020. Native Seedling Colonization on Stockpiled Mine Soils Is Constrained by Site Conditions and Competition with Exotic Species. Minerals. 10:361. 10-15. 
• Baldos, O.C. 2009. Assessment of Hydroplanting Techniques and Herbicide Tolerance of Two Native Hawaiian Ground Covers with Roadside Re-Vegetation Potential. Master’s Thesis from the Graduate Division of the University of Hawaii. 1-150.
• Carr, W.W. 1977. Hydroseeding of Forest Road Slopes for Erosion Control and Resource Protection. Master’s thesis from The University of British Columbia. 
• Colorado County. 2016. Urban Drainage and Flood Control District – Urban Storm Drainage Criteria Manual Volume 2. 
• Pawelek et al. 2015. Comparing Three Common Seeding Techniques for Pipeline Vegetation Restoration: A Case Study in South Texas.