Growing grass on steep slopes is always a challenge to get started. Wind and rain tend to wash the seeds down before they have a chance to be established. The steepness of the slope is difficult to walk on, and impossible for machinery to drive over without making ruts in the soil or tipping the machine. Commercially, developers use trucks equipped with high-powered spray nozzles that will spread seed, fertilizer, and water in one mix over the area from hundreds a feet away. You can seed a steep bank on your property by hiring a company that uses this type of truck or by following a few instructions.
Prepare a trench at the top of the slope to hold the matting in place. Remove about 6 inches of soil in depth and 6 inches in width. Remove any sticks or large rocks from the slope so the mat has good soil contact.
Seed the area with a deep-rooted grass that can stand up to wind and rain. If the slope is too steep to mow, you can add some perennial flower seeds to the mix for a way to naturalize the slope. Spread the seed by throwing the seed over the area, trying to keep it as uniform as possible.
Secure the mat to the top of the slope, in the trench with large staples that are at least 8 inches long. Replace the dirt that you removed earlier by placing it in the trench over the mat.
Roll the mat down the hill and secure with more staples at the bottom. Gentle slopes only need one staple every square yard while very steep slopes will need two.
Sprinkle the mat with a good layer of hay and water lightly every day until you see green growth appearing. Stop watering and allow the roots to grow deeper into the soil. The straw or hay will eventually disappear, either from wind or by decomposing into the soil.