by Bethany Hayes (revised and updated)
The 30-second version: First, get clear on why you’re lining the bottom, because the right material depends entirely on the job. If you’re putting a bed on grass or weeds and want to smother them, plain cardboard or a thick layer of newspaper is the cheapest and best choice — it blocks growth, then breaks down and feeds the soil. If your problem is burrowing animals like gophers or voles, you want hardware cloth, which does nothing for weeds but everything for pests. And please skip one piece of old advice: do not put a layer of rocks or gravel at the bottom for “drainage.” It does the opposite — it actually traps water higher in the bed. Most beds deeper than about ten inches don’t strictly need anything at all.
First, decide what job you actually need done
When I built my first raised beds, I lined the bottoms because a blog told me to, without ever asking why. That’s backwards. The material only makes sense once you know the problem you’re solving, and there are really three different problems people are trying to fix:
The most common is smothering the grass or weeds underneath so they don’t grow up into your new bed. This is the big one, and it has a clear best answer.
The second is keeping burrowing animals out — gophers, voles, moles tunneling up from below. Totally different material, totally different job.
The third isn’t really a problem at all: filling depth cheaply so you buy less soil. That’s a legitimate goal, but the bottom of the bed is for bulky organic material, not a “barrier,” and it’s its own topic (we have a whole guide on filling raised beds cheaply).
Sort out which of those you’re doing, and the choice below gets easy.
Do you need to put anything down at all?
Honestly? Often not. If your bed is deeper than about ten inches and sits on open ground, the roots have plenty of room and the grass underneath will die on its own once it’s buried under that much soil and cut off from light.
The one time I’d skip a bottom layer entirely is when a bed is shallow (under six inches) — a barrier in a shallow bed can crowd roots and do more harm than good. In that case, manage weeds from the top with mulch instead.
And if you do nothing over existing grass, just know that tough perennial grasses like Bermuda can eventually push through. For most lawns, though, deep soil plus a season of darkness is enough.
Quick reference: which material for which job
| Material | Best job | Lasts | Watch out for |
|---|---|---|---|
| Cardboard | Smothering grass/weeds | 4–6+ months, then feeds soil | Remove tape, labels, glossy coatings |
| Newspaper | Smothering grass/weeds | Months; faster than cardboard | Use thick layers (10+ sheets) |
| Leaves | Cheap fill + slow weed block | 6–12 months | Not a true weed barrier on its own |
| Wood/logs | Cheap fill + moisture hold | Years | Never pressure-treated wood |
| Hardware cloth | Stopping burrowing animals | Many years | Does nothing for weeds |
| Burlap | Eco-friendly weed block | A few years | Frays; fiddly to cut |
| Landscape fabric | Long-term weed block | 10+ years | Long-term downsides — see below |
| Stones/gravel | (Drainage myth — skip it) | Forever | Traps water; don’t use for drainage |
| Nothing | Deep beds on open soil | — | Won’t stop tough perennial weeds |
The 9 options, one by one
1. Cardboard — the one I’d reach for first
For smothering grass and weeds, plain corrugated cardboard is cheap, abundant, and genuinely the choice most extension gardeners recommend. Lay two overlapping layers across the bottom, wet it down, and fill on top. It blocks light long enough to kill the grass, then breaks down over four to six months and lets soil microbes move freely between your bed and the ground below.
The only real rule: pull off the tape, shipping labels, and any glossy or waxy coating first. Plain brown cardboard with standard printing is fine — modern box inks are overwhelmingly soy- and water-based — but tape and plastic coatings don’t break down and aren’t something you want in your soil.
2. Newspaper — cheapest of all
Newspaper does the same job as cardboard and costs essentially nothing, especially if you collect it from friends. Spread a thick layer — think ten or more sheets — across the bottom and wet it so it stays put while you fill. As it breaks down it adds carbon, feeding the microbes that build healthy soil. It decomposes faster than cardboard, so use it generously; thin layers won’t last long enough to do the smothering job.
3. Landscape fabric — works, but I’ve stopped recommending it
Landscape fabric is durable, permeable, and blocks light, and the good brands last a decade. On paper it sounds ideal. In practice, most extension services now steer people away from it in garden beds, and after using it I understand why. Over time, weed and grass roots grow into the fabric, mulch above it erodes to expose it, and tough grasses like Bermuda push right through. Worse, it can leave you with a synthetic sheet permanently buried in your soil. If you want a long-lasting barrier, I’d reach for cardboard refreshed each year, or burlap. If you do use fabric, lining just the bed’s inner walls (not the bottom) is a tidier way to keep grass from creeping in.
4. Burlap — the eco-friendly middle ground
Burlap is a nice compromise if you want something sturdier than newspaper but don’t love the idea of plastic fabric. It’s made from jute plant fibers, lets water through, blocks light to suppress weeds, and takes a few years to break down. The downside is purely practical: it frays as you cut it, which makes sizing it to the bed a little fiddly.
5. Leaves — free, but not a true barrier
If you’ve got a yard full of autumn leaves, a thick layer at the bottom of a deep bed is a great way to add free organic matter — they’ll break down over six to twelve months and enrich your soil. Just be clear about what they do and don’t do: leaves are fill and future compost, not a reliable weed barrier. If smothering grass is your goal, put cardboard down first and pile the leaves on top of that.
6. Hardware cloth — for animals, not weeds
If your trouble is gophers, voles, or moles tunneling up into the bed, hardware cloth (galvanized wire mesh — sometimes mis-called “hardware fabric”) is the answer. Staple it across the bottom before you fill. It won’t suppress a single weed — the mesh openings are wide open to light — but it stops burrowing animals cold and lasts for years. The nice thing is you can combine it with cardboard or newspaper on top to get both weed control and animal protection.
7. Stones and gravel — skip this one (it’s a myth)
This is the one I most want to correct. The old advice to put a layer of rocks at the bottom “for drainage” is one of gardening’s most stubborn myths, and it actually backfires. Water doesn’t drain faster through a coarse layer beneath finer soil — it hesitates at the boundary and creates what’s called a perched water table, leaving your soil wetter, higher up, than it would be otherwise. You can end up with soggy roots, the exact opposite of what you wanted. (Our own Q&A on rocks in raised beds and our raised-bed myths article both dig into the science.) Stones also leave gaps weeds grow through and are expensive to buy in quantity. There’s just no good reason to line a bed bottom with them.
8. Wood and logs — cheap bulk fill
Logs, branches, untreated scrap planks, and wood chips at the bottom of a deep bed are a smart way to save on soil while holding moisture — it’s the same principle behind hugelkultur, where buried rotting wood acts like a sponge. The wood breaks down over years, slowly feeding the bed. Two cautions: never use pressure-treated lumber (the preservatives can leach into your soil), and don’t pack solid planks so tightly that water can’t move past them.
9. Nothing — a perfectly valid choice
You’re genuinely not required to put anything down. Over a deep bed on open soil, burying the grass under a foot of soil will kill most of it, and you skip the cost and labor entirely. Just plan to stay on top of weeds from above with mulch, since nothing underneath is suppressing them.
Common Questions
What’s the single best thing to put at the bottom?
For the most common goal — killing the grass and weeds under a new bed — plain cardboard, tape and labels removed, two layers thick. It’s cheap, it works, and it improves your soil as it breaks down.
Should I put gravel or rocks at the bottom for drainage?
No. It’s a myth that won’t die. A coarse layer under finer soil traps water higher in the bed instead of helping it drain. Leave the bottom open to the ground below, or use organic material.
Will cardboard or newspaper ink hurt my plants?
Modern newspaper and box inks are almost all soy- or water-based and safe. The things to remove are plastic tape, shipping labels, and glossy or waxy coatings, which don’t break down.
My bed sits on a patio or concrete — does that change things?
Yes. With no soil underneath, drainage matters more, and a bottom that holds water is a real risk. You’ll want a bed deep enough for roots, drainage holes or an open slatted bottom, and bulky organic material (not rocks) above that.
Do I need a barrier if my bed is really deep?
Usually not for weeds — a foot or more of soil smothers grass on its own. The exception is burrowing animals, which a deep bed won’t stop; that’s a job for hardware cloth.
Final Thoughts
The honest answer to “what do I put at the bottom of a raised bed?” is “it depends what you’re trying to fix.” Smothering grass? Cardboard or newspaper. Keeping animals out? Hardware cloth. Filling depth cheaply? Logs and leaves. Worried about drainage? Do less, not more — leave the bottom open and skip the rocks. Match the material to the job and you’ll spend less money, less effort, and end up with a healthier bed.
Leave a Reply