Will Cedar Chips Kill Grass? Yes — Here’s the Right Depth
Cedar chips kill grass once spread 3 to 4 inches deep, thick enough to block sunlight completely, but a thin 1-2 inch layer can actually help grass by holding soil moisture instead. Bermuda, zoysia, and St. Augustine grass spread through underground runners and need 5 to 8 inches to fully stop regrowth. This guide covers the exact depth for killing grass on purpose, what cedar mulch does to soil pH, and how to keep nearby plants safe.
How Thick Should Cedar Chips Be to Kill Grass?
The depth you use determines whether cedar chips kill grass or help it grow. A 1-2 inch layer insulates roots and holds moisture, which can actually support grass. A 3-4 inch layer blocks enough sunlight to kill most common lawn grasses within 4 to 8 weeks. Aggressive spreading grasses like Bermuda, zoysia, and St. Augustine store energy in underground runners and often need 5 to 8 inches of coarse chips to fully stop regrowth, according to Iowa State University Extension.
| Cedar Chip Depth | Effect on Grass | Best Use |
|---|---|---|
| 1–2 inches | Insulates roots, holds moisture — can help grass survive | Mulching around existing lawn edges or beds |
| 3–4 inches | Blocks sunlight, kills most common grasses in 4–8 weeks | Converting a lawn section into a garden bed |
| 5–8 inches | Needed to stop regrowth of runner grasses (Bermuda, zoysia, St. Augustine) | Reclaiming ground from aggressive spreading grass |
Best Grass-Killing Barrier Pick
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GDNaid Heavy Duty Weed Barrier Landscape Fabric (4ft x 100ft) – $34.99 Lay this under cedar chips instead of cardboard for a barrier that blocks 100% of light regardless of mulch depth — the most reliable way to kill grass this guide covers.
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Cedar Chips vs. Other Mulch for Killing Grass
Cedar chips aren’t the only option for smothering grass, and they aren’t always the cheapest. Here’s how cedar stacks up against the alternatives most homeowners consider.
| Mulch Type | Cost | Best For |
|---|---|---|
| Cedar chips | Higher than hardwood/pine | Long-lasting weed control, insect-repelling scent |
| Hardwood/pine mulch | Lower | Faster nutrient release, budget projects |
| Landscape fabric + mulch | Moderate | Most reliable grass kill — blocks light completely regardless of mulch depth |
Landscape fabric under a thinner layer of any mulch, including cedar, kills grass more reliably than relying on mulch depth alone — it blocks 100% of light no matter how the chips settle or blow around over time.
How to Use Cedar Chips to Kill Grass on Purpose
- Mow the grass low: Cut it as short as your mower allows so the mulch layer has less height to cover.
- Add a barrier (optional but recommended): Lay cardboard or landscape fabric directly over the grass to block light completely.
- Spread cedar chips 3-4 inches deep: Use 5-8 inches over Bermuda, zoysia, or St. Augustine grass.
- Water the area well: Moisture helps the chips settle and speeds up smothering.
- Check back in 4-8 weeks: Pull back a section to confirm the grass has died before planting anything new.
Downsides of Cedar Chips You Should Know
- Soil acidity: Cedar can lower soil pH over time, which matters for plants that need neutral or alkaline soil.
- Nitrogen depletion: Microorganisms breaking down the chips temporarily pull nitrogen from the soil, which can stress plants growing nearby.
- Repels beneficial insects: Cedar’s natural oils can deter bees, ladybugs, and earthworms, not just pests.
- Slower nutrient release: Cedar breaks down slower than hardwood or pine mulch, so it feeds the soil less over the same period.
“Thick mulch works, but the grass that comes back through it fastest is always the runner-type grass along the edges where the layer got thin — check those spots first before assuming the whole bed is clear.”
Frequently Asked Questions
Will cedar chips kill grass?
Yes, but only at the right depth. A 3-4 inch layer blocks enough sunlight to kill most grass within 4-8 weeks. A thin 1-2 inch layer won’t kill grass and can even help it grow by holding soil moisture.
How thick should cedar chips be to stop grass from growing?
About 3 to 4 inches for most lawn grasses. Bermuda, zoysia, and St. Augustine grass spread through underground runners and typically need 5 to 8 inches to fully stop regrowth.
Can cedar chips be used as mulch around plants?
Yes, cedar chips work well as mulch and help retain soil moisture while suppressing weeds. Avoid putting them directly against seedlings or small plants, since the natural compounds in cedar can slow young growth.
Will cedar chips change the soil or plant health?
Cedar chips can slightly acidify soil over time and temporarily reduce available nitrogen as they break down. Most established plants tolerate this fine, but it’s worth watching plants that need neutral or alkaline soil.
Is it better to remove grass before putting down cedar chips?
Yes. Mowing the grass low first, and adding a cardboard or landscape fabric barrier underneath the chips, makes the grass die faster and more reliably than chips alone.
