What is an erosion control blanket?
Erosion control blankets are used to prevent erosion and enhance seed germination. There are many variations of erosion control blankets. The majority of blankets are comprised of netting, stitching, and a medium. Blankets will have a top net, top and bottom net, or no net. The netting is used to keep the medium from floating or washing away and to give structure to the blanket. The netting can be plastic or made of a natural fiber. The plastic netting can be UV stabilized to increase its longevity or no UV to ensure the net breaks down quickly. The natural fiber netting is weaved, the junctions are not fixed to ensure wild life does not become entangle in the netting. The medium of blankets typically consist of straw, coconut fiber, or wood fiber. Blankets with straw or coconut fiber typically are manufactured to weigh 1/2 pounds per square yard. Wood fiber blanket will range in weight 1/2 pound to 1.25 pounds per square yard. Stitching is typically polyester which is photodegradable, or biodegradable stitching is cotton or rayon.
Cost
If the only concern about your project is cost and the least expensive is what you seek, then a single net straw blanket is the blanket that should be installed. That blanket should be in the range of $0.35 to $.50 per square yard depending on the quantity being purchased. If the thought process is “The most expensive must be the best, and the best is what I use”, then the double netted 100% coconut blanket is definitely the choice. That blanket will have a cost range $.80 to $1.05 per square yard. For a degradable erosion control blanket it’s not cheap, the coconut fibers are a product of the southeast Asia and need to be shipped. Don’t want the cheap blanket because everyone knows “you get what you pay for”, but high cost material is not in the budget. This is where the wood fiber blanket sits on the cost scale. The wood fiber blanket will run you in the range $.50 to $0.80 per square yard depending on quantity and weight type of blanket.
Function
All the blankets will perform admirably in their designed situation. One of the primary functions is to prevent soil erosion of the seed bed. This is done in two way, by simply lying on the soil the blanket’s contact and weight will prevent the soil from washing. The other method, blankets prevent raindrop erosion by being a cover for the soil. The second primary function is to assist in seed germination. This maybe the more important of the two functions. Establishing thick vegetation will prevent most soil erosion. Blankets provide cover to prevent seed mobilization, they add warmth to speed the germination rate and some blankets can retain moisture also to assist in germination and seedling growth. Blankets’ lifespans are dependent on it matrix and netting type. Straw tends to break down in three months, wood fiber up to a year and coconut fiber will last 2 to 3 years. These time frames will vary based on weather and time of year placed. As an example, blankets installed late in the year that endure winter conditions will not start degrading until warmer conditions bring about microbial action.
Vegetation
Vegetation is the main goal, but establishing vegetation is easier said than done. If conditions are perfect, blankets probably are not needed. Conditions are typically not perfect. Adverse conditions include but are not limited to: weather is too hot; weather is too cold; to much rain; not enough rain; too shady; ground is steep; ground has a slight waterway; poor top soil. Soil moisture is too much or too little.
The type of vegetation is also a factor. The typical grass (lawn) seedlings sprout between 7 and 21 days. Some native grasses will will take up to 120 days to germinate and over two years to become fully established.
Longevity
The above conversation on vegetation leads to the functional longevity of blankets. This seems to be pretty straight forward approach. Typical lawn grass geminates fairly quickly and straw blankets should be fine. However, maybe soil condition are not ideal and the grass takes a while longer to become established. The native grasses that take up to 2 years to get established, the coconut fiber blanket is most likely the blanket to use. The wood fiber blankets depending on the amount of wood fiber in the matrix up to 24 months. When conditions are not ideal and you are looking for some insurance (safety factor), the wood fiber blankets may be the answer.
There are some hybrid blankets such as a straw/coconut blanket. It’s matrix is 70% straw and 30% coconut and is rated by the industry as a 2 year blanket. An personal opinion here, if 70% of the matrix will be gone in less than a year, how can it be rated a two year blanket?
Application
Will you be using the blankets on a slope or will they be used in a swale and channel? Single net blankets can be used on slopes up to 3:1 (Horizontal : Vertical), Double net blankets’ up to 1:1 slopes. The slope length and the amount of rainfall will determine the matrix used. Channel and swales are typically a double net blanket application. Again, channel length and volume of water will help determine the matrix used. I general, I will recommend a wood fiber doubled netted product in this application or will suggest using a Turf Reinforcement Mat. This is a non degradable mat.
Conclusion
So there is more than meets the eyes when it comes to the erosion control blanket and what to use. Every situation is different. All the blankets will perform as designed as long as it is being used in its proper space. A great place to learn and get a whole lot more in depth is the Erosion Control Technology Council’s web site. Also, calling up the local supply store can be helpful. Here are some detail you should be prepared to give. Did the area have an existing stand of grass?, Is the area heavily shaded?, Is it on a slope and if so how steep and how long? Can you irrigate the area? What grass type are you planting?
Coleman Moore Company sells all these of the above blankets discussed, even the straw/Coconut blanket. There erosion control blanket can do wonders for getting you grass established and minimizing erosion if put in the proper application and installed properly. As a parting comment, typically seed is cheap, do yourself a favor and use more than the recommended rate.