What is the Difference Between Hydroseeding and Hydromulching

The difference between hydroseeding and hydromulching can be somewhat confused. As seed and mulch distribution systems they have become popular planting processes and are supplanting many of the common planting methods that have historically been used. This is largely because of the flexible and adaptive nature of both the hydroseeding and hydromulching processes, together, with their ability to be used on difficult terrain, and a success rate that is as good as even exceeds traditional methods. 

Both hydroseeding and hydromulching use identical hydraulic distribution systems and there is some cross over in terms of their use cases with them often used in conjunction with one another and also used as a mixed process. It is because of this that the terms are frequently conflated, with hydroseeding being used interchangeably for both. Yet, there are some important differences between the two processes and between the practical implementations of hydromulching and hydroseeding.

Hydroseeding and Hydromulching: The Differences in Process

Hydroseeding is the hydraulic broadcast distribution of seeds containing a mix of water, fertilizer, mulch, seed, and tackifiers, amongst other materials. This is delivered under pressure through a hose or mounted turret gun/cannon. Hydroseeding is popular because it is an efficient, affordable, and sustainable method for creating new vegetation, commonly grass, rehabilitating and revegetating cleared lands such as construction or mine sites, and erosion control.

Hydromulching is very similar in that it also uses the same hydraulic process. However, with hydromulching the makeup of the slurry mix that is broadcast is different. With hydromulching, the seed is not part of the mix and a difference in the type of mulch that is utilized. The mulches used in hydromulching are more fibrous than in hydroseeding.

While in hydroseeding you can use mulches such as paper cellulose, straw or wood fiber and paper blended mulches, with hydromulching you are likely to be using full wood fiber mulch, bonded fiber matrix (BFM) or flexible growth medium (FGM).

This is because hydromulching is more orientated to industrial applications, particularly erosion control. The mulch, used in erosion control has additional functions. Its purpose is to form temporary barrier across the targeted area in order to stabilize the soil and reduce erosion while underlying vegetation grows through.

In terms of application, hydroseeding is a single process. However, hydromulching can be either a single or split process, the split process involving hydroseeding.

The much that is used, of course, depends upon a project’s requirements. If a split process is being utilized then the ground would be hydroseeded first. This would be done with around a third of the volume of mulch that would be used when hydroseeding alone as the process. This is then followed by hydromulching over the hydroseeded area, using three times the volume of mulch. It is generally considered that a split process is more effective than a single process for erosion control.^[1]

Hydroseeding and Hydromulching: Differences in Application

There are several use cases for which hydroseeding and hydromulching can be used. The main uses are for creating new vegetation, revegetating ground and erosion control. It is within these roles that hydroseeding, hydromulching, a combination of both or a mixed process are utilized. 

Aspects of each use case determine which process is used. In general though, most of the use cases will involve vegetation and or revegetation, which means that hydroseeding is the predominant process. 

However, there are certain use cases, particularly in terms of erosion control and dust control for which hydromulching is required. The establishment of erosion control blankets highlights this. Although the laying of an erosion control blanket is often preceded by seeding or hydroseeding (the split process mentioned above), the actual blanket itself is put down to create a protective ‘matrix’ to stop the erosion process. The blankets are formed by the interlocking of the mulch fibers that can hold around a hundred times their weight in water which then acts as a slow release of moisture to the soil.

Equipment Differences

Another difference between the two, in regards to application, is the different machinery that need to be used. The type of mulch used where hydromulching is required forms an extremely thick slurry. This slurry needs more powerful machines to broadcast it.

When using hydromulching you are going to need a machine that is capable of distributing the mulch efficiently. This will almost certainly require a paddle agitated machine in contrast to most standard hydroseeding applications which can be delivered with jet agitated machines. So, while hydroseeding can be applied with any type of machine the reverse is not true of hydromulching.

Mixed Process

As we have already discussed, where hydromulching is used with hydroseeding, a split process is usually considered the most effective in terms of end results. This doesn’t mean that some contracts don’t use a single pass method. 

The reasons for this tend to be time and cost-based, though if executed correctly a mixed single process can also deliver results on a par with the split process. This mixed process is referred to as either hydroseeding or hydromulching, although as it includes the seed hydroseeding is a more accurate term.

If using a single process, the combination of hydroseeding and hydromulching would mean that the mix would consist of wood fiber or fiber matrix mulches, thus producing heavier slurry. As with hydromulching, this would require a paddle agitated machine for its distribution.

Summary:

Although the hydurlic process is the same and many of the materials that are used in the mix are similar, sometimes even interchangeable, there is a crucial difference between hydroseeding and hydromulching. This lies squarely in the use of seed, a variable that determines the main use case of an application, more often than not denoting different mulches and different distribution equipment.

That the difference appears slight and is compounded by the use of the two processes in tandem,  particularly in industrial use cases, often leads to the processes being conflated as just hydroseeding. This even more so when a mixed process is used.

Yet, hydroseeding and hydromulching are two distinct processes, with different purposes. Yes, they can be used in tandem or combined but both have a specific use. The choice of which process is used will come down to contract specifications and preferences of the contractor.

Commonly asked Questions

In hydroseeding what is a slurry?

Slurry is the viscous material produced by mixing the components required for hydroseeding or hydromulching. It is broadcast under pressure, via hose or turret gun, on to the targeted area. Slurries usually contain water, seed (if hydroseeding), mulch, fertilizer, tackifiers and dye as their main components. The thickness and exact composition dependent on the  nature of the job at hand.

Notes

[1] United States Department of Agriculture: Hydromulching