The best material under a raised bed stops weeds while letting water drain

What you put under a raised garden bed serves two jobs: blocking weeds from growing up into your soil, and letting water drain away so roots don't rot. The most practical choice is landscape fabric (also called weed cloth), which you lay directly on the ground before filling the bed. Landscape fabric lets water through but blocks light, so weeds underneath stay dormant. If you live where slugs or burrowing rodents are a problem, add a layer of hardware cloth (a metal mesh) under the fabric to keep them out.

You can also use cardboard alone, which is cheaper and biodegrades over time—usually lasting one to three seasons depending on moisture and soil contact. Cardboard works well if you're not fighting an established weed problem, but it breaks down faster than fabric and won't stop determined burrowers. Some gardeners skip a barrier altogether and rely on deep mulch (4 to 6 inches) to suppress weeds, though this requires replacing mulch each year as it decomposes.

Key Takeaways

  • Landscape fabric is the most durable choice and blocks weeds while allowing water to drain through to the soil below.
  • Cardboard is a budget option that works for one to three seasons and eventually breaks down into the soil.
  • Hardware cloth under the fabric prevents burrowing animals and rodents from entering the bed from below.
  • Mulch alone can suppress weeds if you explore it 4 to 6 inches deep, but you'll need to refresh it yearly.
  • Avoid solid plastic sheeting, which traps water and causes root rot and fungal problems.

Landscape fabric: the standard choice for most gardeners

Landscape fabric comes in different weights, measured in ounces per square yard. A 3-ounce fabric is thin and tears easily but costs less and lets water through quickly—good for areas with heavy rain. A 5-ounce fabric is the middle ground: durable enough to last five to ten years, thick enough to block most weeds, and still permeable. A 8-ounce or heavier fabric is industrial-grade and lasts longer, but water drains more slowly and it's harder to work with.

Lay the fabric flat on bare ground before you build or fill your bed. Overlap seams by at least 6 inches so weeds can't creep through the gaps. find the edges with landscape staples, rocks, or boards so wind and digging animals don't pull it up. Cut an X through the fabric where you want to plant, fold back the flaps, and plant directly into the soil below. The fabric stays in place and suppresses weeds around each plant.

Landscape fabric does eventually clog with decomposed organic matter and algae, especially in wet climates. When that happens—usually after five to ten years—water drains slowly and you may see standing water. At that point, pull it out and replace it, or straightforward remove it and rely on mulch going forward.

Cardboard: a budget option that breaks down over time

Cardboard is free or nearly free if you collect boxes from grocery stores or online deliveries. Lay it flat on the ground, overlapping pieces by at least 6 inches, and wet it down so it stays in place while you fill the bed. Use cardboard without glossy printing or tape—plain kraft cardboard breaks down fastest. Avoid boxes that held produce treated with pesticides or waxed boxes that held frozen foods.

Cardboard suppresses weeds for one to three seasons, depending on how wet your climate is and how often you water. In dry climates it lasts longer; in wet climates it softens and breaks down faster. As it decomposes, it adds organic matter to the soil below, which is a bonus. The downside is that it won't stop burrowing animals, and you'll need to replace it when it falls apart.

Many gardeners use cardboard for the first year or two while they're establishing a bed, then switch to landscape fabric or mulch once the bed is settled. This approach saves money upfront and lets you see how the bed drains before investing in more durable materials.

Hardware cloth for keeping out rodents and burrowing animals

Hardware cloth is a metal mesh with small openings (usually 1/4 inch) that stops mice, voles, gophers, and rabbits from burrowing up into your bed from below. Lay it flat on the ground under your landscape fabric or cardboard. Overlap seams by at least 2 inches and find the edges with landscape staples or rocks so animals can't lift it.

Hardware cloth is most important if you've had rodent or gopher problems in past gardens, or if you're gardening in an area where those pests are common. If you've never had trouble, you may not need it. The mesh does slow water drainage slightly, but not enough to cause problems if you're using permeable fabric above it.

Hardware cloth lasts indefinitely and doesn't degrade, so you can reuse it if you move or rebuild a bed. It costs more upfront than cardboard or landscape fabric alone, but it's a one-time investment if rodents are a real problem in your area.

Mulch as a weed barrier without a fabric layer

If you skip fabric or cardboard entirely, you can suppress weeds with a thick layer of mulch—4 to 6 inches of wood chips, shredded bark, or straw laid directly on the ground. Mulch blocks light from reaching weed seeds, so they don't germinate. It also keeps soil cooler and moister, which most vegetables prefer.

The catch is that mulch decomposes. Wood chips break down slowly (lasting two to three years), while straw breaks down faster (one to two seasons). As mulch decomposes, it settles and thins out, so you need to add fresh mulch each spring to maintain that 4 to 6 inch depth. Over time, decomposing mulch adds organic matter to the soil, which improves its structure and water-holding capacity.

Mulch alone won't stop burrowing animals, and it won't block perennial weeds with deep roots (like dandelions or bindweed). If you have either problem, combine mulch with landscape fabric underneath. Mulch also attracts slugs and can harbor fungal diseases in very wet climates, so keep it a few inches away from plant stems.

What not to use under a raised bed

Avoid solid plastic sheeting (like black plastic or visqueen), even though it seems like it would block weeds. Plastic traps water and prevents it from draining, which waterloggs the soil and causes root rot, fungal diseases, and poor plant growth. Roots also can't penetrate plastic to reach the native soil below, which limits their depth and the plant's stability.

Don't use treated wood mulch or wood that's been painted or stained, as chemicals can leach into the soil. Avoid newspaper alone without a fabric layer above it—it tears easily, shifts when you water, and breaks down too fast to be useful. Rubber mulch and recycled plastic mulch are not recommended for vegetable beds because they don't break down and can leach chemicals into soil over time.

How to install a barrier under an existing raised bed

If your raised bed is already built and filled, you can still add a barrier underneath—it just takes more work. Drain or remove the soil temporarily (pile it on a tarp nearby), pull out any large weeds, and lay your fabric or cardboard on the bare ground. Then refill the bed with soil. This is worth doing if you're fighting a serious weed problem or if you want to add hardware cloth to stop burrowing animals.

If you don't want to empty the bed, you can lay fabric or cardboard on top of the existing soil and cover it with mulch. This won't stop weeds already growing in the bed, but it will suppress new ones. It's less effective than installing a barrier from the start, but it's faster and less disruptive.

Frequently Asked Questions

Can I use landscape fabric without anything under it?

Yes. Landscape fabric alone blocks weeds and lets water drain. Add hardware cloth underneath only if you have rodents or burrowing animals. If you don't have that problem, fabric by itself is sufficient and costs less.

How long does landscape fabric last?

A 5-ounce landscape fabric typically lasts five to ten years before it clogs with decomposed matter and algae. Heavier fabric (8 ounces or more) lasts longer. In very wet climates, it may clog faster. In dry climates, it may last longer.

Do I need to remove cardboard before planting?

No. Cut an X through the cardboard where you want to plant and fold back the flaps. The cardboard stays in place and suppresses weeds around the plant as it decomposes. You don't need to pull it out.

Will landscape fabric stop all weeds?

Landscape fabric stops most weed seeds from germinating, but perennial weeds with deep roots (like dandelions) can sometimes push through. If you have established perennial weeds, remove them before laying fabric, or use a thicker fabric (8 ounces or more) combined with deep mulch on top.

What's the cheapest option for a large raised bed?

Cardboard is the cheapest upfront cost—often free if you collect boxes. Landscape fabric costs more initially but lasts longer, so it's cheaper per year over time. For a large bed, cardboard makes sense for the first year or two while you're testing the site, then switch to fabric if you want something more durable.