Building and filling a raised garden bed

A raised bed warms up earlier in spring, gets around compacted or poor soil, has fewer stubborn weeds, and brings the garden to a more comfortable height. It can also lower the risk where the ground has lead or other contaminants. The trade-off is that a raised bed acts like a container and dries out faster than the ground, and the taller it is, the more often it needs water.

What you need

• Boards, metal panels, blocks or other side material, and corner pieces
• A drill and exterior screws, if you're building with wood
• A shovel or garden fork
• A level and a tape measure
• Topsoil and plant-based compost
• Hardware cloth, if mice or chipmunks are a problem

Steps

1. 1

   Pick the spot

   Tomatoes, peppers and eggplant need at least 6 to 8 hours of sun a day. Lettuce, kale, scallions and radishes manage with less. Put the bed where a hose reaches.

   15 min

2. 2

   Size it

   Make it narrow enough that you can reach the center without stepping in, since stepping in packs the soil. A few inches of height is often enough. Go 1 to 2 feet high on hot pavement, and about 27 inches for a gardener in a wheelchair. Several smaller beds make it easier to rotate crops than one long one.

   15 min

3. 3

   Check the side material

   Don't use old lumber, railroad ties or wood treated with chromated copper arsenate (CCA), which can leach arsenic into vegetables. Newer treated wood uses copper instead. Use only wood labeled for ground contact, and line the inside to keep copper out of the soil.

   10 min

4. 4

   Clear and loosen the ground

   Kill the grass or weeds where the bed will go, then loosen the top layer of soil with a fork or shovel. Skip a barrier underneath, which stunts roots. If you killed the grass under a tarp or cardboard, take it off first.

   45 min

5. 5

   Build the frame

   Keep boards to 6 feet or shorter so they're less likely to warp or break, and set them heartwood side in, so any warping bows outward. Check that the frame is level. Lay hardware cloth across the bottom if mice or chipmunks tunnel in your yard.

   60 min

6. 6

   Work out the soil

   Multiply length by width by depth in feet and divide by 27 for cubic yards. A bed 4 by 8 feet and 1 foot deep holds about 1.2 cubic yards.

   5 min

7. 7

   Fill it

   Mix about 2/3 to 1/2 loam or sandy loam topsoil with 1/3 to 1/2 plant-based compost. Add some sand if the topsoil is heavy clay. Skip potting soil, which dries out too fast, and go light on manure, which is high in phosphorus.

   60 min

8. 8

   Water it in

   Soak the soil and let it settle, then top it up.

   15 min

9. 9

   Check the soil after it settles

   Look across the bed and add soil anywhere it sank below the rest.

   2 min

Keeping it going

Test the soil every 2 to 3 years and add compost or fertilizer as the results call for. Heavy yearly compost can build up phosphorus and salts that burn young roots. Water close to the soil, with a soaker hose or watering can, to keep the leaves dry and cut down on disease. An established raised bed needs little or no tilling.

Raised ground beds

The simplest raised bed has no sides at all. It's a flat-topped mound of soil 6 to 8 inches high. Keep it to 2 1/2 feet wide if you can reach only one side, or up to 5 feet if you can work from both. Mounded beds stay put from year to year, needing only a rake to reshape them each spring. Bring in soil only from a source free of plant diseases, lead and pesticides.