Native Grass Restoration and Management
Native Grass Seeding
A light layer of organic matter can aid the germination of native seed and protect the site from erosion. The type and quantity of organic matter can make a great difference in the results.
This is one of the mostly commonly cited methods of seeding and erosion control, and our least favorite. Hydromulch is wood fiber. It is usually made from ground up recycled newspapers, and spread hydraulically from a hydromulch truck or trailer, along with the seed, fertilizer, organic glues and whatever else you want to spray onto the site.
Hydromulch fiber is usually applied at 2000 lb/ac, which sounds like a lot, but looks like a thin layer of blotter paper after it's been applied. The mulch coats the soil surface and seals in some of the moisture. The seed is mixed with the mulch on top of the soil, but not covered by it. As a result, germination is reduced. One rule of thumb is that you need to double your normal seed mix to get the same results with hydromulch.
We find that few species successfully germinate with hydromulch. In the Bay Area, Hordeum brachyantherum, Festuca rubra, Elymus glaucus and Bromus carinatus do fairly well, but we don't see much from the others. I have never seen Nassella pulchra germinate from hydromulch.
The main types of straw are: wheat straw, rice straw and native grass straw. Wheat straw is the easiest to purchase and apply. Wheat straw, however, contains weed seed. It used to be the most popular to use, but it has fallen out of favor, because of the weed seed problem.
Rice straw is the most popular straw in use for restoration projects. It does contain weed seeds, but they are wetland weeds, so don't pose a problem for most restoration projects. Be careful using rice straw near wetlands. I have not heard of a problem using rice straw near wetlands, but the weed threat exists. I sometimes switch back to wheat straw right along the wetland edge.
Native grass straw is available from native grass growers. I have not purchased or used any, only because of the logistics of procuring it. I cannot give any feedback on its use.
Never use straw bales that have become wet. Once straw has become wet, it is almost impossible to spread properly. It can also rot while in the bale.
Wheat straw is the easiest to spread by hand. It flows well and lays flat on the surface. Rice straw, however, is baled with longer peices, and the straw is rough to the touch. Rice straw does not spread evenly, and tends to make a lumpy finish. You need to work harder to make it even.
Some large contractors own straw blowers. You feed the bales into the blower. A set of whirling chains beat the bales apart. The action of the chains throws the straw pieces out of a chute for a distance of 20 or 30 ft. The straw makes a very even surface after passing through the blower.
The application rates in specifications usually call for 2 tons of straw per acre. I find that to be too heavy. Native seedlings will not grow through thick straw, although weeds will. Thick straw is a way to select for weeds and against natives. The straw should be applied at the lightest rate possible that still provides erosion control. You should be able to look down and see the soil through the straw. If you can't, it's too thick. This usually comes out around 1 1/2 tons per acre. When applying rice straw, I use around 25 bales per acre.
If straw is applied on the surface, it could easily blow away before the first rain. There are two ways to reduce this problem. The more reliable method is to spray a light layer of hydromulch and tackifier over the top to glue it into place. You would use tackifier with hydromulch at 500 lb/ac. The second way is to wet the straw down. When straw becomes wet, it lays down on the ground and also gets a bit sticky. It will glue itself together somewhat. A light watering may not be enough.
Compost can be used as a combination seedbed and mulch. It will provide an excellent medium for germination and early growth, while retaining the moisture the seedlings require. Make sure that you use fully composted material. It should smell sweet, and have not aroma of active decomposition. If the material is not fully composted, it will have very little available nitrogen, and the seedlings will be stunted.
The compost may be 1inch thick or more, depending on the slope. The seed would be applied on the surface and raked in. No additional mulch would be required.