How to fill a tall raised bed without buying 2 yards of soil

Volume goes up with every inch of height. A 4 x 8 ft bed measured inside holds 32 cubic feet at 12 inches deep, 48 at 18 and 64 at 24. That last one is 2.37 cubic yards, or 32 bags of 2 cu ft, for a single bed.

Oklahoma State Extension published a fix in February 2026: put logs, branches, twigs and leaves in the bottom of the bed and keep the purchased soil for the top. Its fact sheet says this cuts the soil you have to buy by a lot. It's the raised-bed version of a hugelkultur mound, an old way of burying wood under soil.

Source: Oklahoma State Extension HLA-6478, hugelkultur, checked October 10, 2026.

• 17 inminimum bed height for a wood layer (Oklahoma State)Oklahoma State Extension HLA-6478, hugelkultur, October 10, 2026
• Lower halfof the bed for logs, branches and leavesOklahoma State Extension HLA-6478, hugelkultur, October 10, 2026
• 32 cu ftof soil saved in a 4 x 8 bed, 24 in deepArithmetic
• 16 bagsof 2 cu ft instead of 32Arithmetic

Lay the largest logs on the bottom, then branches, then small twigs, and pack leaves into the gaps. Oklahoma State lists hardwoods as the best choice: alder, aspen, birch, cottonwood, maple, oak, poplar and willow. Fall is a good time to gather all of it. Storm limbs, pruned branches and the leaves you'd otherwise bag are free.

Source: Oklahoma State Extension HLA-6478, hugelkultur, checked October 10, 2026.

1. 1

   Check the height

   Measure inside the boards. Oklahoma State says the wood layer works in beds at least 17 inches tall. Three 2x6 boards stack to 16 1/2, so a bed that size gets soil all the way.

   Source: Oklahoma State Extension HLA-6478, hugelkultur, checked October 10, 2026; NIST, PS 20-20 American Softwood Lumber Standard, checked October 10, 2026.

2. 2

   Work out the top half

   Put the inside length and width into the raised bed soil calculator with half the height as the depth. That's the soil and compost to buy. Keep a few extra bags for the soil that runs down into the gaps.

3. 3

   Lay the wood

   Logs first, then branches, then twigs, until the pile reaches about half the bed's height. Fill the spaces with leaves.

   Source: Oklahoma State Extension HLA-6478, hugelkultur, checked October 10, 2026.

4. 4

   Water and tamp each layer

   Soak each layer before the next one goes on, and press it down with a tamper. Oklahoma State says this helps the wood break down and closes up air pockets.

   Source: Oklahoma State Extension HLA-6478, hugelkultur, checked October 10, 2026.

5. 5

   Add soil and compost on top

   Fill the upper half with planting soil and compost, water it in, and add more where it sinks. Plant roots should sit in this layer, not in the wood.

   Source: Oklahoma State Extension HLA-6478, hugelkultur, checked October 10, 2026.

One 4 x 8 ft bed measured inside. Cubic feet = 32 x height in inches / 12; bags rounded up.

On open ground, the half-and-half split leaves plenty of soil for most crops once a bed reaches 24 inches. A 17 or 18 inch bed has only 8 1/2 to 9 inches of soil on top. That matches the 8 inches Oregon State and Maryland Extension give, but falls just short of the 10 inches UGA Extension says most garden crops need. On concrete or paving, Maryland wants 12 to 24 inches of mix for peppers, tomatoes and squash, so a bed there should be tall enough to keep at least 12 inches of soil above the wood.

Source: OSU Extension FS 270, raised bed gardening, checked October 10, 2026; UMD Extension, growing vegetables in raised beds, checked October 10, 2026; UGA Extension C 1027-4, raised garden bed dimensions, checked October 10, 2026.

The wood rots, so the bed settles more than an all-soil bed does. Oklahoma State says to top it up with soil or compost each year until most of the wood has broken down. Illinois Extension calls settling a fact of raised bed gardening even without wood, and says a few inches of compost a year usually keeps up. The fact sheet also notes that wood can tie up nitrogen while it breaks down. That's one more reason to keep the roots up in the soil layer.

Source: Oklahoma State Extension HLA-6478, hugelkultur, checked October 10, 2026; Illinois Extension, refreshing raised bed soil, checked October 6, 2026.