What You Need Before You Start
A raised bed needs four things: a frame, soil, a location that gets sun, and a way to keep pests out if you want one. The frame is the only part you have to build or buy. Everything else you can add as you go, and you can change it later without starting over.
The frame itself can be wood, composite material, metal, or plastic. Wood is cheapest and easiest to work with if you use untreated cedar or pine boards. Composite lasts longer but costs more. Metal and plastic are durable but harder to find in standard sizes. Pick whatever fits your budget and the look you want — the soil and plants do not care what the frame is made of.
You will also need soil to fill it. Do not use dirt from your yard. Buy a mix of topsoil, compost, and perlite or coarse sand, or buy a bagged raised bed soil mix. A 4-by-8-foot bed that is 12 inches deep needs about 32 cubic feet of soil. Most garden centers can tell you how many bags that is, or you can calculate it yourself by multiplying length times width times depth in feet, then dividing by 27.
Key Takeaways
- Build or place your frame on level ground, then fill it with a mix of topsoil and compost rather than yard dirt.
- Choose a spot that gets at least six hours of direct sun for vegetables, or three to four hours for leafy greens.
- Add a bottom barrier if you are worried about weeds or burrowing pests, but it is not required for most gardens.
- Water the soil after you fill the bed so it settles, then wait a few days before planting.
Choosing the Right Location
Sun is the biggest factor. Most vegetables need six to eight hours of direct sunlight a day. Leafy greens like lettuce and spinach can get by on three to four hours. If your yard is shaded, put the bed where the sun hits longest, usually the south or west side of your house.
Check the spot at different times of day before you commit. A place that looks sunny in the morning might be in shade by afternoon. If you have a choice between morning sun and afternoon sun, morning is better because it dries dew and reduces disease.
Avoid low spots where water pools after rain, and stay away from tree roots if you can. Roots will compete with your plants for water and nutrients. If you have to build near trees, use a deeper bed — 18 inches instead of 12 — so your plants have room to grow down.
Building or Placing Your Frame
If you are building a wooden frame, use untreated cedar or pine boards, typically 2 inches by 8 inches or 2 inches by 10 inches. Cedar lasts longer than pine but costs more. Avoid pressure-treated wood — the chemicals can leach into soil. Cut the boards to length, then join the corners with corner brackets, wood screws, or by overlapping the ends and screwing through one board into the end of the other.
Make sure the frame is level before you fill it. Use a level tool across the top in two directions. If the ground is not level, dig out the high side a little and fill in the low side. A frame that is off by more than an inch will cause water to pool on one end and dry out on the other.
If you bought a prefabricated frame, assemble it according to the instructions, then place it on level ground. Do not worry about making it perfect — a quarter-inch of slope is fine and will actually help water drain.
Adding a Barrier and Filling With Soil
A barrier on the bottom keeps weeds from growing up into your bed and stops burrowing pests like moles and voles. It is optional. If your yard has a lot of weeds or you know you have burrowing pests, use it. If not, you can skip it and save money.
If you use a barrier, lay down landscape fabric or hardware cloth (a metal mesh) before you add soil. Landscape fabric lets water through but blocks weeds. Hardware cloth blocks both weeds and animals but can rust over time. Staple or pin it to the inside of the frame so it does not shift when you pour soil.
Pour soil into the frame until it is full. The soil will settle over the first few weeks, so fill it to the top. Water it thoroughly — the bed should be damp all the way through. Let it sit for two or three days before you plant. This gives the soil time to settle and the water to distribute evenly.
Preparing for Planting
After the soil has settled, check the level again. If it dropped more than an inch, add more soil. You want the bed full so water does not run off the sides.
If you are planting seeds, wait until the soil temperature is right for what you are growing. A soil thermometer costs a few dollars and tells you when to plant. Most vegetables need soil between 60 and 70 degrees Fahrenheit. If you are planting seedlings you bought from a nursery, you can plant right away as long as the soil is damp.
Add mulch on top of the soil after you plant — two to three inches of wood chips or straw. Mulch keeps weeds down, holds moisture in, and keeps soil cool. Leave a small gap around the base of each plant so air can circulate.
Watering and Maintenance Through the Season
Raised beds dry out faster than in-ground gardens because water drains through the bottom and sides. Check the soil every day or two by pushing your finger an inch into it. If it feels dry, water. In hot weather, you may need to water every day.
Water early in the morning so the soil has time to absorb it before the sun gets hot. Water the soil, not the leaves — wet leaves invite disease. If you have a soaker hose or drip line, lay it on top of the soil under the mulch. It will save you time and use less water than hand-watering.
As the season goes on, the soil will break down and settle. Add compost on top in mid-summer and again in fall. This keeps the soil rich and brings the level back up. At the end of the season, you can add a thick layer of compost or aged manure and let it sit over winter — it will break down and be ready to plant in spring.
Adding Pest Protection if You Need It
If rabbits or deer are a problem in your area, you may want a fence or netting. A fence around the bed should be at least two feet tall for rabbits and four feet for deer. Bury it six inches into the ground or bend the bottom outward to stop rabbits from digging under.
For insects like beetles or caterpillars, row covers — lightweight fabric that lets light and water through — work well. Drape them over the plants and anchor the edges with soil or stakes. Remove them when the plants flower if you need bees to pollinate.
Netting over the top stops birds from eating berries and seeds. Use netting with small holes so birds do not get tangled. Remove it as soon as the fruit is gone so birds can help control insects.
Frequently Asked Questions
How deep should a raised bed be?
Twelve inches is the standard depth and works for most vegetables. Root vegetables like carrots and beets do better in 18 inches. Shallow-rooted plants like lettuce can grow in eight inches. Deeper is always better if you have the space and budget — it gives roots more room and holds more water.
Can I use wood from a pallet or old fence?
Pallets are risky because you do not know what chemicals they were treated with. Old fence wood might be pressure-treated, which can leach into soil. Stick with untreated cedar or pine, or buy new boards. The cost difference is small compared to the risk.
What if the ground underneath is concrete or asphalt?
A raised bed on concrete works fine. The barrier on the bottom becomes more important because roots cannot go down into soil. Use a deeper bed — at least 18 inches — and make sure water can drain somewhere. Drill a few holes in the concrete if you can, or accept that water will sit on top and evaporate slowly.
How often should I refill the soil?
Soil breaks down and compacts over time. Add two to three inches of compost each year to keep it rich and at the right level. Every three to five years, you may want to empty the bed, refresh the bottom with new compost, and refill. This is a good time to check the frame for rot or damage.
Can I plant in a raised bed right after I fill it?
You can, but waiting two or three days is better. The soil needs time to settle and the water to distribute evenly. If you plant right away, the soil will sink around your plants as it settles, and watering will be uneven. A short wait saves trouble later.