Bamboo barrier depth and thickness: 24 in (60 mil), 30 in (80 mil) or 36 in (100 mil)

Which depth do I need?

It depends on two things: your USDA hardiness zone and how tall your bamboo grows.

How to read it: find your zone, then the size of your bamboo. Zones 4–7: 24 in for bamboo up to about 25 ft, 30 in for anything larger, timber bamboo included. Zone 8: 30 in. Zones 9–11: 36 in. Can't name your bamboo or its mature height? Use the larger-bamboo row for your zone (30 in in zones 4–8, 36 in in 9–11).

Don't know your zone? Enter your ZIP code on the USDA Plant Hardiness Zone Map.

Two things can move you one depth deeper: loose or sandy soil, and what a test hole turns up. Both are below.

How tall will my bamboo get?

Go by mature height, not by how tall the canes are today. A young grove can take years to reach full size. Typical mature heights from a bamboo nursery's listings:

• Small runners, such as Pleioblastus and Sasa: most stay a few feet tall.
• Golden bamboo (Phyllostachys aurea): usually 15 to 20 ft, up to about 35 ft.
• Yellow groove (Phyllostachys aureosulcata): about 25 ft, up to about 30 ft.
• Timber bamboo, such as Japanese timber bamboo (Phyllostachys bambusoides) and Moso (Phyllostachys edulis): often about 40 ft, and up to 60 or 70 ft.

Golden bamboo and yellow groove sit close to the 25 ft line. If you can't tell whether yours will stay under about 25 ft, use the larger-bamboo row.

What if my soil is loose or sandy?

Go one depth deeper: 24 in becomes 30 in, and 30 in becomes 36 in. Rhizomes push through loose soil more easily, so some run deeper.

If the chart already gives 36 in, stay at 36 in, the deepest Bamboo Shield. In any soil, firm the backfill as you fill the trench, and keep compost out of the bottom.

Example: zone 6, a small runner that stays well under 25 ft, in sandy soil. The chart gives 24 in. Sandy soil moves it to 30 in.

How do I check my own yard with a test hole?

A test hole shows how deep rhizomes run in your soil, instead of an average.

1. Call 811 before you dig.
2. Dig a hole about 30 in deep at the edge of the grove, on the line where the trench will go. Keep one side straight and clean.
3. Look at that side. Rhizomes are thick and jointed, with buds and roots at the joints. Roots are thin and stringy.
4. Measure from the soil surface down to the deepest rhizome you find.
5. Choose the depth whose trench bottom sits at least 4 in below that rhizome. The trench bottom is the barrier depth minus 2 in.

Worked example: the deepest rhizome is at 20 in. The 24 in barrier's trench bottom is only 2 in below it (22 − 20 = 2), too close. The 30 in barrier's is 8 in below it (28 − 20 = 8), so use 30 in.

If the hole and the chart give different depths, use the deeper one. Planting new bamboo? There is nothing to test yet, so go by the chart and your soil.

What if I don't know what bamboo I have?

Use the larger-bamboo row for your zone: 30 in in zones 4–8, 36 in in zones 9–11.

Not sure whether it runs or clumps? Plan for running bamboo. Running vs clumping bamboo shows how to tell.

Does clumping bamboo need a barrier?

Most clumping bamboo spreads slowly and doesn't need one. If you want a firm edge around a clumper anyway, near a pool, foundation or property line, use 36 in.

What if rhizomes are already past the line?

Dig them out before or while you set the barrier. No depth stops a rhizome that is already outside.

How far down does each barrier reach?

Most running-bamboo rhizomes stay in the top 12 to 18 in of soil. You leave 2 in of barrier above the finished soil, so the trench is the barrier depth minus 2 in.

Set with a 2 in lip, the three depths reach 22, 28 and 34 in down. That puts their bottom edges 4, 10 and 16 in below the 18 in mark (22 − 18 = 4, 28 − 18 = 10, 34 − 18 = 16). The extra depth is room for the few rhizomes that run deeper. How deep bamboo rhizomes grow explains what changes how deep they run.

Can I use the 18 in Sidewalk Shield for bamboo? No. Set with a 2 in lip, it reaches only 16 in down (18 − 2 = 16), still inside the layer where rhizomes run. Sidewalk Shield is made for tree roots along sidewalks, curbs and driveways: see the tree root barrier install manual.

Does thickness matter: 60, 80 or 100 mil?

Yes, but you don't choose it on its own. Each depth comes in one thickness: 60 mil at 24 in, 80 mil at 30 in and 100 mil at 36 in. None is thinner than 60 mil.

A mil is a thousandth of an inch, so 60 mil is 0.06 in, or about 1.5 mm. Puncture strength is given in lbf (pounds of force).

In the ASTM D4833 test, a lab clamps the sheet in a ring and pushes a steel rod into it. The rod is about 5/16 in (8 mm) wide. The result is the most force the sheet takes before the rod breaks through. It is a way to compare sheets, not a forecast of what a rhizome will do.

Each step up in thickness adds puncture strength: 130, then 155, then 200 lbf. But depth is what you are choosing, so let the chart set it. University of Maryland Extension suggests at least 60 mil for bamboo, and says 80 mil may be ideal for more mature or vigorous colonies.

Thickness is only one part of the job. At any thickness, a barrier can leak at a joint, over a buried top edge or under loose backfill. Firm the backfill as you fill the trench.

Is 100 mil overkill?

In zones 9–11, no: 36 in (100 mil) is the depth for any running bamboo there. In zones 4–8, the chart stops at 30 in (80 mil), timber bamboo included. There, choose 36 in when loose or sandy soil or a test hole moves you up from 30 in, or for a firm edge around a clumper.

Compared with 30 in, the 36 in means:

• A 34 in trench instead of 28 in, so 6 in more digging
• 1.5 times the weight per foot (1.5 ÷ 1.0 = 1.5)
• A 70 ft longest piece instead of 100 ft, so a 150 ft run has 2 joints instead of 1
• A higher price per foot. The Bamboo Shield page shows current prices.
• A stiffer sheet that is harder to bend around a tight curve

Against 24 in, the gap is bigger: 12 in more digging (34 − 22 = 12) and 2.5 times the weight per foot (1.5 ÷ 0.6 = 2.5).

How long is the longest piece, and how many joints will I have?

Each cut ships as one box, and boxes stay under 110 lb. Deeper barrier weighs more per foot, so its longest piece is shorter: 175 ft at 24 in, 100 ft at 30 in and 70 ft at 36 in.

A full-length piece weighs about 100 to 105 lb (175 × 0.6, 100 × 1.0 or 70 × 1.5). Plan on two people to carry it.

A longer run ships as more than one piece. Add 12 in for each joint, round up to the next 5 ft, and order one connecting kit per joint.

Worked example: a 150 ft straight run

1. 24 in: 150 ft is less than 175 ft, so one piece covers it. No joint, so order 150 ft and no kit.
2. 30 in: 150 ft is more than 100 ft, so you need 2 pieces and 1 joint. Add 12 in for the joint: 151 ft. Round up to the next 5 ft: 155 ft, cut as 80 ft and 75 ft, plus 1 kit.
3. 36 in: 2 pieces of 70 ft cover only 140 ft, so you need 3 pieces and 2 joints. Add 12 in for each joint: 152 ft. Round up to 155 ft, cut as 55, 50 and 50 ft, plus 2 kits.

A closed loop counts joints differently, because its two ends meet. How much bamboo barrier do I need works through loops at each depth.

Common mistakes

• Guessing the size. If you can't name your bamboo or its mature height, use the larger-bamboo row for your zone.
• Forgetting the soil. Loose or sandy soil takes one depth deeper than the chart. At 36 in, stay at 36 in.
• Mixing depths in one line. A 24 in piece clamped to a 30 in piece is only 24 in deep at the joint. Use one depth and its matching kit.
• Burying the lip. Rhizomes can cross over the top of any depth. Keep 2 in showing, and keep mulch and soil off it.
• Paying for thickness, then taping a joint. Tape is not a seal. Clamp every joint with the connecting kit.

How do I order it?

Choose your depth and length on the Bamboo Shield page. You order by the foot in 5 ft steps, with a 20 ft minimum, and shipping is free to the lower 48 states. Add one connecting kit for each joint, in the same depth as the barrier.

All three depths are black and made in the USA.

Read the Bamboo Shield install manual before you start. It covers the trench, the tilt, the joints and the yearly check. Call 811 before you dig.

FAQ

What depth do I need for timber bamboo?

30 in (80 mil) in zones 4–8, and 36 in (100 mil) in zones 9–11. Large timber bamboo in a cold climate: 30 in is fine. In loose or sandy soil, go one depth deeper, so 30 in becomes 36 in. At 36 in, stay at 36 in.

Does climate change the depth?

Yes. The chart goes by USDA zone. Zones 4–7: 24 in for bamboo up to about 25 ft, 30 in for anything larger, timber bamboo included. Zone 8: 30 in. Zones 9–11: 36 in, for any running bamboo.

Can I get the 24 in depth in 80 or 100 mil?

No. Each depth comes in one thickness: 24 in is 60 mil, 30 in is 80 mil and 36 in is 100 mil. For a thicker sheet, step up a depth. The 30 in barrier is 80 mil, measures 155 lbf in the ASTM D4833 puncture test and reaches 28 in down with its 2 in lip.

Is this HDPE strong enough?

Bamboo Shield is HDPE, made in the USA. Every depth is at least 60 mil, the minimum University of Maryland Extension suggests for bamboo. In ASTM D4833 puncture testing it measures 130 lbf at 60 mil, 155 lbf at 80 mil and 200 lbf at 100 mil.

Why is the 36 in piece only 70 ft?

Each cut ships as one box, and boxes stay under 110 lb. Deeper barrier weighs more per foot: about 0.6 lb at 24 in, 1.0 lb at 30 in and 1.5 lb at 36 in. The heavier the foot, the shorter the piece. At 70 ft, the 36 in piece weighs about 105 lb (70 × 1.5).