Most raised beds have no bottom — the soil sits directly on the ground

A raised garden bed does not require a bottom. In fact, the most common setup has no barrier between the soil and the earth below. The bed is straightforward a frame — wood, metal, composite, or stone — filled with soil that rests on whatever ground is underneath.

This open-bottom design works because plant roots can grow down into the native soil, and water drains through to the ground. Earthworms and beneficial organisms move freely between your bed and the surrounding earth. For most gardeners growing vegetables, herbs, or flowers, this is the standard approach and it works well.

Key Takeaways

  • Raised beds without a bottom allow roots to extend into native soil and water to drain naturally, which is the most common setup.
  • A bottom barrier becomes necessary if your ground soil is contaminated, compacted clay, or if you are dealing with burrowing pests like gophers or moles.
  • Hardware cloth (a metal mesh) is the most durable choice for pest barriers; landscape fabric deteriorates and does not stop determined rodents.
  • Raised beds on concrete or asphalt require a bottom to prevent root damage and allow drainage, and they perform worse than beds on soil.
  • Adding a bottom slows drainage and can trap water, so if you use one, drill or punch holes to prevent pooling.

When you need a bottom barrier

Add a bottom if your native soil is contaminated with lead, arsenic, or other toxins — common in urban yards or near old industrial sites. A bottom keeps your vegetables and herbs separated from that soil. You can test your soil through your local extension office, which will tell you whether contamination is present.

A bottom also makes sense if burrowing pests are a real problem. Gophers and moles tunnel up into raised beds and eat roots and bulbs. Voles do the same. If you have seen these animals in your yard or your neighbors have, hardware cloth stapled to the underside of the frame will stop them. Landscape fabric will not — rodents chew through it.

Very compacted clay soil that does not drain well may also warrant a bottom with drainage holes, because it can trap water around roots. However, breaking up the native clay first is usually a better solution than adding a barrier.

Hardware cloth versus landscape fabric

Hardware cloth is a galvanized or stainless steel mesh with small square openings, usually 1/4 inch. It lasts 10 to 15 years or longer and stops gophers, moles, and voles. Staple it to the underside of your frame so the mesh extends slightly up the sides. It costs more upfront but outlasts fabric by years.

Landscape fabric is a woven or nonwoven synthetic material that lets water through but blocks weeds. It does not stop burrowing rodents — they chew holes in it within weeks or months. It also degrades in sunlight and typically lasts 3 to 5 years before tearing. Use it only if your concern is weeds from below, not pests.

If you choose hardware cloth, drill or punch 1/4-inch holes every 6 inches across the bottom to may support water does not pool. If you use landscape fabric, the same drainage holes prevent standing water.

Raised beds on concrete or asphalt

If your bed sits on concrete, asphalt, or another hard surface, you must add a bottom with drainage holes. Without one, water has nowhere to go and roots rot. Drill or punch holes every 6 inches in a grid pattern so water can escape.

Beds on hard surfaces also perform worse than beds on soil because roots cannot extend downward and the soil dries out faster in summer. If you have a choice, place your bed on earth rather than pavement. If you must use concrete, add a bottom with drainage and plan to water more often.

How to install a bottom barrier

Measure the inside dimensions of your frame. Cut hardware cloth or landscape fabric to fit, with 2 to 3 inches extra on all sides. Lay it flat on the ground inside the frame. Fold the extra material up the inside walls and staple it to the frame every 6 inches, pulling it taut as you go.

Before filling with soil, drill or punch 1/4-inch holes in a grid pattern across the bottom — one hole every 6 inches in each direction. This prevents water from pooling. If you are using hardware cloth, the mesh openings themselves provide some drainage, but additional holes speed the process.

Fill the bed with soil as usual. The barrier sits between the soil and the ground, so you will not see it once planting begins.

What happens without a bottom

Without a bottom, your raised bed integrates with the surrounding soil ecosystem. Roots grow down into native earth, which can be good or bad depending on what is below. If the native soil is healthy and well-draining, your plants thrive. If it is clay, compacted, or contaminated, your plants struggle.

Beneficial organisms — earthworms, mycorrhizal fungi, beneficial bacteria — move freely between your bed and the ground. This generally improves soil health over time. Water drains naturally, so you are less likely to overwater accidentally.

The downside: if burrowing pests are present, they will find your bed. If native soil is poor, you are fighting it rather than working with it. And if contamination is present, it can move into your vegetables.

Depth and drainage without a bottom

A raised bed without a bottom should be at least 8 to 10 inches deep for most vegetables and herbs. Shallower beds dry out too quickly and do not give roots enough room. Deeper beds — 12 to 18 inches — are better for root crops like carrots and potatoes, and for long-term perennials like asparagus.

Drainage happens naturally through the open bottom, but the quality of native soil matters. If your ground is clay or compacted, water moves slowly and roots may sit in moisture. If it is sandy or loamy, water drains quickly and you may need to water more often. Amending the native soil before you build the bed — working in compost or aged manure — improves both drainage and nutrient content.

Frequently Asked Questions

Can I use a plastic sheet as a bottom?

Plastic sheets trap water and rot roots, so no. If you need a barrier, use hardware cloth or landscape fabric with drainage holes. Plastic is too impermeable and will kill your plants within a season.

Will tree roots grow up into my raised bed?

Yes, if a tree is nearby. Tree roots seek water and nutrients and will grow into your bed soil. Hardware cloth stops them, but landscape fabric only slows them down. If tree roots are a problem, hardware cloth stapled to the bottom is your best option.

Do I need a bottom if I am growing in containers inside a raised bed?

No. If your plants are in pots or grow bags sitting inside the frame, the bottom of the bed does not matter. The containers provide their own barrier. This setup is useful if you want to rotate crops or move plants around.

How deep should the bottom barrier be buried?

It should not be buried — it sits on top of the ground inside your frame. Fold the edges up the inside walls and staple them to the wood or frame material. This keeps the barrier in place while allowing water to drain underneath at the edges.

Can I add a bottom to an existing raised bed?

Yes, but it is easier to do before filling. If your bed is already planted, you can carefully remove the soil, install the barrier, and refill. For an empty bed, straightforward lay the barrier down, find it to the frame, drill drainage holes, and fill with soil.