Start with the frame and location

A raised bed begins with a frame—usually wood, composite, or metal—sitting directly on the ground where you want to garden. You do not need a foundation or concrete. The frame holds soil in place and keeps it separate from whatever is underneath: compacted earth, grass, or poor native soil.

Pick a spot that gets at least six hours of direct sun per day for vegetables, or three to four hours for leafy greens. Make sure water can drain away; a low spot that pools after rain will waterlog your plants. If you are building on grass, you can lay cardboard under the frame first to kill the grass underneath, though it is not required—the raised soil will eventually smother it.

Measure your space before you buy materials. Standard sizes are 4 feet by 8 feet, 4 feet by 4 feet, or 2 feet by 4 feet. A 4-by-8 bed is long enough to reach from both sides without stepping in it, and deep enough (10 to 12 inches) for most vegetables. Smaller beds work fine if space is tight.

Key Takeaways

  • A raised bed frame sits directly on the ground and needs at least six hours of sun and good drainage to work well.
  • Wood frames should be untreated cedar, composite, or galvanized metal—never pressure-treated wood, which can leach chemicals into soil.
  • Fill your bed with a mix of topsoil, compost, and peat moss or coconut coir, not just garden soil alone.
  • A 4-by-8-foot bed 10 to 12 inches deep holds roughly 32 cubic feet of soil, which you can calculate before buying.
  • You can plant when ready after filling, though letting the bed settle for a few days helps soil compact naturally.

Choose materials that won't harm your soil

Wood is the most common choice. Use untreated cedar or redwood—both resist rot naturally. Composite boards (plastic and wood fiber) last longer and do not rot, but cost more. Avoid pressure-treated wood, which was historically treated with arsenic and copper compounds that can leach into soil over time. Newer pressure-treated lumber uses different chemicals, but untreated cedar is still the safer choice for food gardens.

Galvanized metal (steel with a zinc coating) is durable and lasts 10 to 15 years. It heats up faster in spring, which some gardeners like. Aluminum is lightweight but dents easily. Avoid untreated steel, which rusts quickly.

You will also need corner brackets or L-brackets to hold the frame square, a level to check that the bed is not tilted, and a drill or screwdriver to assemble it. Most frames are held together with exterior-grade screws, not nails—screws hold better as the wood shifts.

Calculate and buy the right amount of soil

A raised bed needs to be filled with a soil mix, not just topsoil alone. Topsoil compacts over time and can be heavy. A better mix is roughly 40 percent topsoil, 40 percent compost, and 20 percent peat moss or coconut coir. This blend drains well, holds moisture, and gives plants the nutrients they need to start.

To figure out how much soil to buy, multiply length × width × depth (in feet), then divide by 27 to get cubic yards. A 4-by-8-foot bed that is 1 foot deep needs about 1.2 cubic yards of soil. A 4-by-4-foot bed that is 10 inches deep needs about 0.5 cubic yards. Most garden centers sell soil by the bag or cubic yard, so knowing your number before you shop saves time and money.

You can also buy pre-mixed raised bed soil, which is convenient but costs more per cubic foot than buying components separately. If you mix your own, buy each component from a garden center or landscape supplier and blend them in a wheelbarrow or directly in the bed as you fill.

Assemble the frame on level ground

Lay out the boards in a rectangle on the ground where you want the bed to sit. If the ground is very uneven, you can dig out the high spots slightly, but you do not need to level it perfectly. Attach the corners with brackets and screws, checking with a level as you go. The frame does not have to be perfectly level—a slight slope is fine—but avoid tilting it so much that water runs off one side.

If you are using wood, make sure the boards are flush at the corners so soil does not escape between gaps. Tighten all screws firmly; the weight of wet soil will stress the joints over time.

Once the frame is assembled and sitting in place, you are ready to fill it. You do not need to add a bottom layer of landscape fabric or hardware cloth unless you are trying to keep out burrowing animals like gophers or moles.

Fill the bed and let it settle

Pour your soil mix into the frame, breaking up any clumps as you go. Water it lightly as you fill so the soil settles and compacts. Fill until the soil is about an inch below the top of the frame—this leaves room for mulch and prevents soil from washing out when you water.

The soil will settle over the next few days as it absorbs water and compacts naturally. You may need to add more soil after a week to bring it back to the right level. This settling is normal and actually helps the bed become more stable.

You can plant when ready after filling, though many gardeners prefer to wait a few days and water the bed once or twice before planting. This gives the soil time to settle fully and makes it easier to plant seedlings or seeds without the soil shifting under them.

Add mulch and plan your first planting

Once the soil has settled, add 2 to 3 inches of mulch on top—wood chips, straw, or shredded leaves all work. Mulch keeps soil moist, prevents weeds, and breaks down over time to add organic matter. Leave a small gap around plant stems so mulch does not sit directly against them, which can cause rot.

Plan what you want to grow before you plant. Vegetables need different spacing: tomatoes and peppers go 18 to 24 inches apart, lettuce and spinach go 6 to 8 inches apart, and root crops like carrots go 2 to 3 inches apart. A 4-by-8 bed can hold about four tomato plants, or two rows of lettuce, or a mix of both. Sketch it out on paper first so you do not overcrowd.

Water your bed after planting and check the soil moisture every few days. Raised beds drain faster than in-ground gardens, so they dry out quicker in hot weather. A soaker hose or drip line makes watering easier and more consistent than hand-watering.

Maintain your bed year to year

Each year, add 1 to 2 inches of compost to the top of your bed before planting season. This replaces the organic matter that breaks down over time and keeps the soil rich. You do not need to replace all the soil—a well-maintained bed can produce for many years with just annual compost additions.

In fall, you can leave dead plants in the bed and let them break down over winter, or pull them out and compost them separately. Some gardeners plant a cover crop like clover or winter rye in fall to add nitrogen and organic matter, then turn it into the soil in spring.

Check the frame every year for rot (if it is wood) or rust (if it is metal). Cedar lasts 10 to 15 years before it starts to break down. Composite boards last 15 to 20 years. If the frame fails, you can disassemble it and build a new one around the same soil.

Frequently Asked Questions

Do I need to put anything under the raised bed to keep weeds out?

You do not need to, but you can. Landscape fabric or cardboard under the frame slows down weeds from below, though they will still grow from seeds that land on top. If you are building over grass, cardboard under the frame kills the grass underneath. Hardware cloth stops burrowing animals but is not necessary unless you have a gopher or mole problem.

Can I use treated wood if I seal it?

Sealing does not fully prevent leaching, especially over many years and with acidic soil. Untreated cedar or composite materials are safer for vegetable gardens. If you already have a treated-wood bed, it is not an emergency—the risk is low—but replacing it with cedar is the better choice for long-term food gardening.

How deep does a raised bed need to be?

Ten to twelve inches is the minimum for most vegetables. Root crops like carrots and beets need at least 12 inches. Leafy greens can grow in 8 inches. Deeper beds (18 inches or more) give roots more room and hold moisture longer, but they cost more to fill and are harder to reach into.

What if my soil mix settles too much after I fill the bed?

Some settling is normal and expected. If it settles more than a few inches, add more soil mix to bring it back up. This usually happens only once, in the first year. After that, annual compost additions keep the level stable.

Can I build a raised bed in partial shade?

Yes, but choose plants that tolerate it. Leafy greens, herbs like parsley and mint, and some root crops grow well in three to four hours of sun. Tomatoes, peppers, and squash need six hours or more. Check the seed packet or plant tag to see what sun each plant needs.