Build a raised bed frame from untreated wood or composite materials
A raised bed is a bottomless wooden or composite box that sits on top of soil. To build one, you need four boards (typically 2-by-10 or 2-by-12 lumber), four corner brackets or L-brackets, a drill, and wood screws. Untreated cedar, redwood, or composite boards last longest—avoid pressure-treated wood, which can leach chemicals into soil over time.
Cut your boards to length (common sizes are 4 feet by 8 feet or 4 feet by 4 feet), then attach them at the corners using 3-inch exterior-grade wood screws and L-brackets. Drill pilot holes first to prevent splitting. The frame should be square and level before you move it to its final location. If you are building on uneven ground, dig out the high spots slightly so the frame sits stable.
Composite materials like recycled plastic lumber cost more upfront but require no maintenance and last 20+ years. Wood frames typically last 5 to 10 years depending on the species and whether you line the interior with landscape fabric to slow rot.
Key Takeaways
- Untreated cedar or composite boards are safer than pressure-treated wood because they do not leach chemicals into the soil where you grow food.
- A raised bed frame sits directly on soil with no bottom, so roots can reach down into the earth below and drainage happens naturally.
- Fill the bed with a mix of topsoil, compost, and peat moss or coconut coir in roughly equal parts for vegetables and herbs.
- Position your bed where it receives at least 6 to 8 hours of direct sunlight daily, and check that water drains away rather than pooling around the frame.
- Assemble and fill the bed in spring or fall, then let it settle for a week before planting so the soil compacts slightly.
Choose a location with good sunlight and drainage
Raised beds need at least 6 to 8 hours of direct sunlight per day for most vegetables. Morning sun is better than afternoon sun in hot climates because it dries dew and reduces fungal disease, but it still counts as full sun. If your yard is mostly shaded, choose a spot that gets the most light available, even if it is only 4 to 5 hours—leafy greens and herbs tolerate partial shade better than tomatoes or peppers.
Check drainage by pouring water onto the ground where you plan to place the bed. If water pools and sits for more than a few minutes, that spot has poor drainage. Move the bed uphill or to a location where water runs away naturally. Raised beds themselves drain well because soil is elevated, but standing water around the frame can rot the wood and create mosquito habitat.
Avoid placing beds directly under tree branches or near downspouts where they will be constantly wet. Also stay away from areas where lawn chemicals or road salt spray—usually within 10 feet of a driveway or street.
Fill the bed with a soil mixture suited to what you are growing
Do not use garden soil alone—it compacts in a raised bed and drains poorly. Instead, mix three ingredients in roughly equal parts: topsoil (the dark, nutrient-rich soil from the top 6 inches of earth), compost (aged plant matter or composted manure), and a moisture-holding material like peat moss, coconut coir, or aged bark. This combination drains well, holds nutrients, and gives roots room to grow.
For a 4-by-8-foot bed that is 10 inches deep, you will need about 26 cubic feet of soil mix. Buy these materials by the cubic yard or bag and blend them in a wheelbarrow or directly in the bed. If the bed is large, spread each ingredient in layers and mix with a garden fork.
Let the bed settle for a week after filling before you plant. The soil will compact slightly, and you can add more mix if needed. If you are planting when ready, water the bed thoroughly first—dry soil settles faster and more unevenly.
Prepare the ground underneath the bed before assembly
Clear away grass, weeds, and debris from the area where the bed will sit. You do not need to remove the sod entirely, but cut it as short as possible with a mower or weed trimmer. If the ground is very weedy, lay cardboard or several layers of newspaper over the area before placing the frame—this smothers weeds and breaks down over time, adding organic matter to the soil below.
Check that the ground is relatively level. A bed that tilts will have uneven water drainage and may shift over time. If the ground slopes, either choose a different spot or dig out the high side slightly and use the soil to build up the low side.
You do not need to till or dig the soil below the bed. Roots will work their way down naturally, and tilling can bring dormant weed seeds to the surface. The raised bed itself will improve the soil underneath over time as organic matter breaks down.
Add a barrier if you are concerned about soil contamination
If the ground underneath the bed has been treated with pesticides, contains heavy metals, or is contaminated with lead paint dust, line the bottom with landscape fabric or hardware cloth before filling. This creates a barrier between the raised bed soil and the contaminated ground below, though it also prevents roots from reaching deeper soil and can trap water.
Hardware cloth (a metal mesh) is more effective than landscape fabric at keeping out burrowing pests like voles and gophers, but it is more expensive and harder to install. Landscape fabric is easier to lay down and still blocks most contaminants while allowing some water drainage.
If you are growing in a location with unknown soil history—a former industrial site, a lot near a busy road, or land that was recently cleared—a soil test through your local extension office will tell you whether a barrier is necessary. Most residential yards do not need one.
Maintain the bed each season to keep soil healthy
After the first year, add 1 to 2 inches of compost to the top of the bed each spring. This replaces organic matter that broke down over the previous season and keeps the soil rich and crumbly. You do not need to remove old soil—just spread the compost on top and let it work down naturally.
In fall, add a 2 to 3-inch layer of shredded leaves or aged compost to the bed. This protects roots over winter and adds nutrients as it breaks down. By spring, much of it will have decomposed into the soil.
Every few years, check the frame for rot, especially at the corners where water collects. If wood is soft or crumbling, replace that board or section. Cedar and redwood resist rot longer than pine or fir, but all wood eventually needs replacement.
Frequently Asked Questions
How deep should a raised bed be?
Most vegetables need 8 to 12 inches of soil depth. Root crops like carrots and potatoes need 12 inches or more. Shallow-rooted plants like lettuce and herbs can grow in 6 inches. A depth of 10 inches is a good middle ground that works for most gardens.
Can I use treated lumber for a raised bed?
Pressure-treated wood is not recommended for vegetable beds because the chemicals used to preserve it can leach into soil, especially in acidic soil or when the wood is wet. Untreated cedar, redwood, or composite materials are safer choices, though they cost more.
What if my raised bed is in a shady spot?
Leafy greens, herbs, and shade-tolerant crops like lettuce, spinach, kale, and mint will grow in 4 to 6 hours of sunlight. Tomatoes, peppers, and squash need full sun (6 to 8 hours) and will produce poorly in shade. If your only option is a shady spot, focus on greens and herbs.
Do I need to water a raised bed more often than in-ground gardens?
Yes. Raised beds drain faster and dry out quicker than in-ground soil, especially in hot weather or sandy soil mixes. Check soil moisture by pushing your finger 2 inches into the soil—if it feels dry, water deeply. Most raised beds need water every 2 to 3 days in summer, sometimes daily in extreme heat.
Can I build a raised bed on top of concrete or pavement?
Yes, but you will need to add a bottom to the frame or use a very deep bed (at least 18 inches) so roots have enough soil. You will also need to water more frequently because there is no drainage into the ground below. A landscape fabric bottom lets some water drain while keeping roots contained.