Raised Garden Bed FAQ

Do you need a bottom for a raised garden bed?

No, most raised beds work best with an open bottom. Leaving it open lets excess water drain into the ground and lets roots grow down past the frame, which helps plants through dry spells. Two exceptions are worth knowing. If gophers, moles or voles tunnel in your yard, staple ½-inch hardware cloth across the bottom before you add soil, and run it a couple of inches up the inside walls. If the bed sits on a patio or concrete, it has no ground to drain into, so make it 18–24 inches deep and leave gaps or holes at the base for water to escape. Read more in our guide to bed bottoms and base layers.

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

Over lawn or weeds, lay plain brown cardboard with the tape removed, overlapping the edges by several inches, then soak it with a hose. It smothers the grass and breaks down within a season or so, and earthworms move up into the bed as it rots. Add hardware cloth under it if burrowing pests are a problem. In a bed 18 inches or deeper you can fill the bottom third with untreated logs and branches, a method called hugelkultur, to save on soil, but expect the surface to sink as the wood decays, and top it up. Skip the gravel; a rock layer does not improve drainage. Our guide to filling a bed for less covers layering step by step.

What should you build a raised garden bed out of?

Choose by how long you want the bed to last and what you want to spend. Untreated pine or fir is cheapest but usually gives you only 3–7 seasons. Cedar, redwood or cypress holds up for roughly 10–15 years or longer. Steel, either galvanized or powder-coated, can go 15–20 years and beyond with almost no upkeep. Concrete block can last for decades. Fabric beds are light and inexpensive, lasting around 3–5 years, which suits patios and renters. Weigh them side by side in our metal, wood and fabric comparison.

Is it cheaper to build your own raised bed?

Usually, yes, especially for wood. A basic 4x8 pine bed takes three 8-foot boards and a handful of screws, so the lumber bill is low if you own a drill and saw. Cedar costs noticeably more but still tends to come in under a comparable finished bed. Metal beds are the exception, since they are hard to make at home. Keep in mind that the soil often costs more than the frame: a 4x8 bed filled a foot deep swallows 32 cu ft of mix, close to 1.2 cu yd, and bulk delivery by the yard is usually cheaper than bags for that much. See cheap raised garden bed ideas for ways to cut costs.

What should you not fill a raised garden bed with?

Avoid plain native clay, which packs down hard, and straight bagged potting soil, which is costly and shrinks quickly in a large bed. Do not add rocks or gravel for drainage, plastic, scraps of pressure-treated wood, or black walnut wood and leaves, which contain a compound that stunts many vegetables. Fresh manure should be composted first. A dependable fill blends screened topsoil, compost and an aeration ingredient such as pine bark fines, perlite or pumice in roughly a 6:3:1 ratio. The soil recipe guide explains what each ingredient does.

What kind of wood is best for a raised bed?

Cedar is the most popular pick because it resists rot naturally and usually lasts 10–15 years or more. Redwood and cypress are similar where they are sold locally. Pressure-treated lumber made since 2004 relies on copper compounds, and many extension services regard it as fine for vegetable beds; it often lasts 10 years or more. If you want an extra margin of caution, staple plastic sheeting to the inner walls or pick a different wood. Untreated pine is cheap but short-lived. Never use old railroad ties or reclaimed boards treated with CCA, the arsenic-based preservative phased out of home use at the end of 2003. See the best wood for raised garden beds.

How deep should a raised garden bed be?

For most vegetables, 10–12 inches of soil is enough. Shallow-rooted crops such as lettuce, herbs and radishes grow fine in 6–8 inches if the native soil underneath is loosened. Carrots, potatoes and other deep roots need 18–24 inches, as does any bed built on concrete or hard, compacted ground. Elevated table beds usually hold about 8–12 inches. Deeper beds need much more soil, so do the math first: length × width × depth in feet, divided by 27, gives cubic yards. More detail is in our bed depth guide.

What is the easiest thing to grow in a raised bed?

Leaf lettuce is hard to beat: it grows from seed in cool weather, is ready to pick in about a month and manages with 4–6 hours of sun. Radishes, bush beans, herbs such as parsley and chives, and zucchini are also forgiving first crops. Once nights stay above about 50°F, add a tomato or pepper plant or two. Water about an inch a week and mulch to keep the bed from drying out. Our first-season planting guide has a full plan, and growing lettuce in raised beds covers spacing.