What do you put in the bottom of a raised garden bed?

Raised garden beds are a great way to grow vegetables, herbs, and flowers. The contained environment allows you to control the soil quality and drainage, making it easier to grow plants.

When building a new raised bed, one of the most important decisions is what to put in the bottom before adding soil. There are several good options for raised bed bottoms that can provide drainage, prevent weeds, and even deter burrowing animals.

8 Things you should put in the bottom of a raised garden bed

Gravel

A 3–4-inch layer of gravel at the bottom of a raised bed can provide drainage and keep soil from washing out between the boards. Small pea gravel or pea stone works best as it allows water to flow through while still stabilizing the soil. Larger gravel is more difficult for water to penetrate.

Gravel is inexpensive and easy to find at most hardware stores. Just make sure to get a type labeled “weed-free” to prevent seeds from sprouting up through your garden bed. Rinse the gravel first to remove any fine dust that could clog the drainage holes. Level the gravel at the bottom before building up layers of soil.

Landscape Fabric

Landscape fabric, also called geotextile fabric, is another common choice for lining raised garden beds. This woven or non-woven material allows water to pass through while blocking light to suppress weed growth. It comes in different weights; a medium-weight fabric works well for raised beds.

Line the bottom and sides with landscape fabric before filling the bed with soil. Make slits through the fabric where you want to place transplants. The material will keep the soil in place and make weeding easier throughout the season. Landscape fabric typically lasts at least 5 years before needing replacement.

Sand

A 1-2-inch layer of coarse sand or arena sand provides excellent drainage for raised garden beds. Sand particles leave large pore spaces for water to filter through. It won’t compress and clog like fine silt or clay over time. Just be sure to use coarse builder’s sand, not fine play sand or beach sand.

Rinse or screen the sand to remove large debris before pouring it into the bed foundation. Top the sand with a weed barrier like cardboard or several layers of newspaper before adding garden soil. This will keep the layers from mixing over time. Replace the sand layer every 2–3 years as needed.

Crushed Recycled Materials

Crushed recycled materials like concrete, bricks, clay pots, and tiles can be used in place of gravel or sand at the bottom of raised beds. This is a great way to reuse old materials that would otherwise end up in landfills. The crushed material provides excellent drainage underneath the soil.

Stick to clay, terra cotta, or concrete pieces. Avoid using recycled wood, plastics, or anything with paint or sealants that could leach chemicals. Aim for 1-2 inch-sized pieces that leave pore spaces for water to flow through. An added benefit is that the porous material helps aerate plant roots.

Wood Chips

A 2-4 inch layer of wood chips or bark bits at the bottom of a raised bed allows for drainage while suppressing weeds. As the wood decomposes, it adds organic matter to enrich the soil. Use larger shredded bark or wood chunks rather than sawdust or fine wood chips, which can compress and reduce drainage over time.

Cedar and other rot-resistant woods are best since they will break down slowly. This helps prevent nitrogen depletion in the soil as microbes break down the wood. Refresh the wood chip layer annually or every other year. Wood chips are often available for free or cheap from local tree services.

Straw or Leaves

Straw, dried leaves, shredded bark, and other natural materials can be used as a mulch layer underneath the soil in raised garden beds. A 2-4-inch layer helps suppress weeds while allowing water to penetrate. As the organic matter decomposes, it adds nutrients to the soil.

Use course materials like straw rather than grass clippings or finely shredded leaves, which tend to compact and reduce drainage. Avoid diseased plants and walnut tree leaves, which release juglone that is toxic to some vegetables. Top off the mulch layer as it decomposes each year.

Newspaper or Cardboard

Simple cardboard or several layers of newspaper make an effective weed barrier at the bottom of a raised bed. Overlap the pieces to cover the entire surface, and weigh them down with gravel or rocks around the edges.

The paper weed barrier blocks light to kill existing weeds and prevents new seeds from sprouting. As it decomposes over a season, the paper adds organic matter to the soil as well. Just avoid using glossy printed material, which could leach chemicals into the garden bed.

Nothing

It is possible to build a raised bed without putting anything at all under the soil. This works best in boxes built out of rot-resistant wood like cedar or made from poured concrete walls. Quality garden soil in the beds still provides good drainage and plant growth.

Lining the beds is most important in situations where the native soil is heavy clay or poorly draining. If your site has decent soil and drainage, filling the boxes directly with enriched garden soil is fine. You may get a few weeds from the seeds below, but this is easy to manage in a contained raised bed.

Key Considerations

• Good drainage is key; go for materials that leave pore spaces for water flow
• Natural weed barriers like cardboard suppress growth but allow drainage
• Gravel, sand, and landscape fabric are long-lasting options to prevent soil erosion
• Reused or recycled materials reduce waste while improving drainage
• Rot-resistant wood beds may not need any liner, just quality garden soil

The bottom layer is an important factor in getting raised garden beds off to the right start. Consider your climate, soil conditions, and budget when deciding which material is the best fit. With the right foundation, your raised beds will support healthy, productive plants for years to come.