Start with the frame and location
A raised garden bed is a wooden, metal, or composite box you fill with soil and plant into. Building one takes a weekend and requires only basic tools—a drill, saw, and level. The frame itself is the main structure; everything else follows from getting that right.
Choose a spot that gets at least six hours of direct sun for vegetables, or three to four hours for leafy greens. Mark out your bed location and check that the ground is relatively level. If the ground slopes, you can build on the slope, but you'll need to dig out the high side slightly so the frame sits stable. Use a level to check as you go.
Pick a size that lets you reach the center without stepping into the bed—typically 4 feet wide by 8 feet long, or 4 feet by 4 feet for a square. Narrower beds are easier to manage. Height usually ranges from 6 to 12 inches; taller beds are easier on your back and drain better, but cost more to fill.
Key Takeaways
- Build your frame from untreated wood, composite boards, or galvanized metal, and check that it sits level before you fill it with soil.
- Fill the bed with a mix of topsoil and compost rather than garden soil alone, because garden soil compacts and drains poorly in a confined space.
- Plant seeds or transplants directly into the raised bed soil once it has settled for a few days after filling.
- Water raised beds more often than in-ground gardens because soil in a box drains faster and dries out quicker.
- Add a layer of mulch on top of the soil to slow evaporation and keep weeds down.
Assemble the frame from the right materials
Use untreated wood (cedar, redwood, or composite boards work well) rather than pressure-treated lumber, which can leach chemicals into soil over time. Cedar and redwood naturally resist rot. If you use standard pine, it will last four to six years before rotting out. Composite boards cost more upfront but last 15 years or longer.
For a 4-by-8-foot bed, you need two 8-foot boards and two 4-foot boards. Cut them to length if you're starting with longer stock. Drill pilot holes before driving screws to prevent splitting. Use exterior-grade wood screws, 2.5 to 3 inches long, at each corner and every 2 feet along the length. Avoid nails—they work loose as the wood shifts.
Assemble the frame on the ground where it will sit. Check all four corners with a square, then place a level across the top in both directions. If one corner is high, loosen the screws slightly and shim underneath with a flat stone or shim until the frame is level. Tighten the screws again once it's stable.
Fill the bed with the right soil mixture
Do not use garden soil from your yard or bags labeled "garden soil"—it compacts in a raised bed and drains poorly. Instead, mix topsoil and compost in roughly equal parts. For a 4-by-8-foot bed that is 10 inches deep, you'll need about 26 cubic feet of soil, or roughly 1 cubic yard. A cubic yard of topsoil weighs about 1,400 pounds, so order it delivered if possible.
Spread the topsoil first, then layer the compost on top. Use a shovel to mix them together in the bed as you fill. The compost adds nutrients and improves drainage. If you want to add a bottom layer, use cardboard or landscape fabric to block weeds from below, but it's not required—most weeds come from seeds in the air or compost, not from below.
Fill the bed to within 2 inches of the top. The soil will settle over the first week as it absorbs water and compacts slightly. Wait three to five days before planting to let it settle fully.
Plant seeds or transplants into settled soil
Once the soil has settled, you can plant. For seeds, follow the depth and spacing on the seed packet. For transplants (seedlings you've grown or bought), dig a hole slightly larger than the root ball, set the plant in at the same depth it was growing before, and firm the soil around it. Water gently after planting.
Space plants according to their mature size, not their current size. Crowding leads to poor air flow and disease. A spacing guide comes on most seed packets and plant labels. If you're unsure, err on the side of more space—you can always thin seedlings later.
Plant cool-season crops (lettuce, spinach, peas, broccoli) in spring and fall. Plant warm-season crops (tomatoes, peppers, squash, beans) after the last frost date in your area. Your local cooperative extension office publishes frost dates for your region.
Water more frequently than in-ground gardens
Raised beds dry out faster than in-ground soil because they have more surface area exposed to air and sun. Check the soil moisture by pushing your finger 2 inches into the soil. If it feels dry, water. Most raised beds need water every one to two days in summer, depending on heat and rainfall.
Water at the base of plants, not on the leaves, to reduce disease. Early morning is the best time. If you have a soaker hose or drip line, lay it along the soil surface and run it for 20 to 30 minutes. This delivers water slowly and directly to the roots, which is more efficient than overhead watering.
Mulch the soil surface with 2 to 3 inches of wood chips or straw to slow evaporation and keep weeds down. Leave a small gap around the base of each plant so the stem stays dry.
Maintain the bed through the season
Pull weeds as they appear—the raised bed makes this easier because you're not bending as far. Remove dead leaves and spent plants promptly to prevent pests and disease from taking hold. If you see yellowing leaves or stunted growth mid-season, the soil may be depleted. Add a 1-inch layer of compost on top and water it in.
At the end of the season, remove dead plants and add a 2-inch layer of compost or aged manure on top. Leave it over winter; it will break down and enrich the soil for next year. You may need to top up the soil level each year as it settles and decomposes, but you won't need to replace it entirely for several years.
Protect the bed from pests and disease
Raised beds are easier to protect than in-ground gardens because you can cover them with netting or row cloth. Drape the material over hoops or stakes to keep insects off young plants. Remove it once plants flower and need pollination.
Watch for common pests like aphids, slugs, and beetles. Hand-pick larger pests like beetles and caterpillars. For aphids, spray the undersides of leaves with a strong stream of water to knock them off. If problems persist, neem oil or insecticidal soap are low-toxicity options; follow the label directions.
Space plants properly and water at the base to reduce fungal disease. If you see powdery mildew or leaf spots, remove the affected leaves and improve air flow by pruning nearby growth.
Frequently Asked Questions
Do I need to line the bottom of a raised bed?
No, but you can. A cardboard or landscape fabric layer blocks weeds from below, though most weeds come from seeds in the air or compost. If you live in an area with burrowing rodents, hardware cloth (metal mesh) pinned to the bottom will keep them out. For most gardeners, it's optional.
How deep does a raised bed need to be?
Six inches is the minimum for shallow-rooted crops like lettuce and herbs. Ten to twelve inches works for most vegetables. Tomatoes, peppers, and root crops like carrots and beets need 12 inches or deeper. Deeper beds also retain moisture better and give roots more room to spread.
Can I use treated lumber for a raised bed?
Modern pressure-treated lumber is safer than older versions, but untreated wood is still the better choice. Treated wood can leach chemicals into soil over decades of use. Cedar, redwood, and composite boards cost more but avoid the risk entirely.
What's the best time to build a raised bed?
Spring or fall are ideal because you can plant right after filling. You can build in summer or winter too—just wait to plant until the soil has settled and the season is right for what you want to grow.
How often should I replace the soil in a raised bed?
You don't need to replace it entirely. Add 1 to 2 inches of compost each year to replenish nutrients and maintain soil structure. After five to seven years, if the soil is compacted or depleted, you can remove the top half and replace it with fresh soil mixed with compost.