Erosion Control Blanket Installation on a Graded Slope

You seeded a fresh cut slope, laid down a roll of straw blanket, and after the first heavy storm there are muddy rills running underneath it and seed piled at the toe. That is almost never the blanket's fault. Erosion control blanket installation fails at the same few points every time: no anchor trench, poor soil contact, the wrong overlaps and too few staples. Get those right and a $90 roll will hold a 2:1 slope until the grass takes over.

I have laid a lot of these on house pads, road cuts and pond banks over the years. Here is how we do it on our crews, step by step, with the numbers we actually use.

Choose the right blanket for the slope

Blankets are rated by how steep a slope they can handle and how long they last before breaking down. Pick based on your steepest section, not the average.

A standard roll is 8 feet wide by 112.5 feet long, which covers 100 square yards. Order about 15 percent extra to cover overlaps and the anchor trench. If you are weighing blankets against armor stone for a very steep bank, read our comparison of rip rap versus erosion blankets first.

Pick natural netting where you can

Cheaper blankets use photodegradable plastic netting. It can take years to break down in shade, and it traps snakes, turtles and birds. Jute or other natural-fiber netting costs a little more and avoids both problems. Some counties now require it near wetlands.

Prepare the slope before any blanket goes down

The blanket only works if it touches the soil everywhere. Any gap becomes a channel for water.

1. Finish grade first. Rake out ruts, clods and rocks larger than about 2 inches. Fill any rills already on the slope.
2. Fix water coming from above. If runoff from a driveway or a roof sheets over the crest, no blanket will hold. A diversion berm above the slope handles that before you start.
3. Seed and fertilize. Apply seed and starter fertilizer at the rates on the bag. The blanket goes on top of the seed, not under it.
4. Lightly roll or rake the seed in. Seed should be in contact with soil, not sitting loose on a crust.

Erosion control blanket installation step by step

Work from the top of the slope down, and lay the rolls vertically, running up and down the slope rather than across it. Water then flows along the length of the blanket instead of catching under every seam.

1. Dig the anchor trench

At the crest of the slope, about 2 to 3 feet back from the edge, dig a trench 6 inches wide and 6 inches deep across the full width you are covering. This is the single most skipped step and the most important. Without it, water running over the top gets under the first blanket and peels it back.

2. Bury the top of the blanket

Lay the top end of the roll into the trench, running it down one wall, across the bottom and up the other. Staple it to the trench bottom every 12 inches. Backfill with soil, compact it with your boot or a tamper, then fold the remaining blanket back over the filled trench and staple again at 12 inch spacing.

3. Roll it down the slope

Unroll the blanket downhill. Keep it loose enough to follow every dip in the ground, not stretched tight like a drum. A tight blanket bridges over low spots, and those are exactly where water finds its way under.

4. Overlap the edges

Side edges of neighboring rolls overlap 4 inches. Where one roll ends and another starts, overlap 6 inches, with the upper blanket on top of the lower one, like roof shingles. Getting that order backward funnels water straight into the seam.

5. Staple in a proper pattern

Use 6 inch U staples of 11 gauge wire for firm soil, 8 inch or longer for sandy or loose fill. Rough guide:

• Slopes 3:1 or flatter: about 1.5 staples per square yard
• Slopes 2:1: about 2 staples per square yard
• Slopes steeper than 2:1, or in channels: 3 to 4 staples per square yard
• Every seam and overlap: one staple every 12 to 18 inches

A 100 square yard roll on a 2:1 slope needs roughly 200 to 250 staples once seams are included. Boxes of 1,000 run about $60 to $90.

6. Finish the toe

At the bottom, either bury the end in a second small trench or extend the blanket 3 feet onto flat ground and staple it at 12 inch spacing.

Why the heaviest blanket is not always the safest choice

A lot of people buy coconut blanket for every slope on the theory that stronger is better. On a gentle yard slope, I think that is usually wasted money and sometimes worse for the grass. Coconut fiber is dense and slow to break down. On a 3:1 or 4:1 slope with cool-season seed, it can shade seedlings and slow establishment, and it is still sitting there two summers later when the homeowner wants to mow.

Match the blanket to the slope and the seed. Straw double net is the right call for most residential cuts. Spend the difference on more staples and a proper trench, which fix far more failures than a heavier material ever will.

Inspect after every storm until grass is established

Walk the slope after any rain over half an inch for the first two months. Look for:

• Lifted edges or seams. Re-staple right away.
• Rills forming under the blanket. Pull it back, fill and seed the rill, and lay it back with extra staples.
• Bare patches where seed washed. Overseed them and pin a small patch of blanket on top.

Most failures I see on new slopes trace back to small problems left too long. Our article on why a freshly graded slope fails after the first storm goes deeper into what happens in that first month.

Frequently asked questions

Do erosion control blankets go up and down or across the slope?

Lay them up and down the slope, parallel to the direction water flows. This keeps seams running with the water instead of across it. Some manufacturers allow horizontal installs on gentle slopes, but vertical is the safer default.

How many staples do you need for an erosion blanket?

Plan on about 1.5 to 2 staples per square yard on slopes of 3:1 to 2:1, and 3 to 4 per square yard on steeper ground. Add a staple every 12 to 18 inches along every overlap. Check the manufacturer's staple pattern sheet, since it varies by product.

Can grass grow through an erosion control blanket?

Yes. Seed goes down first, and grass grows up through the gaps in the fibers. Straw blankets break down within about a year, leaving the established turf behind. The blanket mainly protects seed and soil until roots can hold the slope on their own.