Honestly, the best way I’ve found is to skip shallow concrete blocks and use helical ground anchors—sometimes called screw piles or earth anchors—paired with a compacted gravel base. Soft soil has two big problems: it compresses under weight, and it doesn’t hold shallow fasteners well. Helical anchors solve both because they are screwed down to a deeper, more stable layer and grip the ground like a screw instead of a stake.
Soft ground often feels firm on top but turns spongy after rain or under load. If you only bolt a bench to a small paver or a short spike, the legs can sink, the bench can rock, and the anchors can gradually pull out. That is why I always focus on two things: load distribution and anchor depth.
Start by prepping the site. Remove the sod, roots, and loose topsoil where the bench will sit. Dig down about 4 to 6 inches, then fill that area with angular gravel or crushed stone. Compact it in thin layers using a hand tamper or plate compactor. This base gives water a place to drain and spreads the bench’s weight over a larger area, which reduces sinking.
Next, mark the bench leg positions on the gravel. I like to set the bench in place first, check the level, and then mark the exact holes. After that, move the bench aside and install the anchors. Use galvanized helical ground anchors that are at least 30 to 40 inches long. If the soil is very soft, wet, or high in clay, go longer—48 inches is not unreasonable. The key is to drive the anchor until you feel a noticeable increase in torque or resistance. That usually means the helix has reached denser soil. You can install these with a heavy-duty impact wrench and the right drive socket, or with a manual turning bar for smaller benches.
Once the anchors are in, bolt the bench legs to the anchor heads. Most helical anchors have a plate or bracket on top. Use hot-dipped galvanized or stainless steel bolts, washers, and lock nuts. If the bench has wooden legs, add a galvanized standoff bracket or a composite shim between the wood and the metal to reduce moisture wicking and rot. Then check the bench with a level in both directions. If one corner is slightly low, you can shim it before fully tightening the bolts.
After leveling, backfill around the anchor heads with gravel rather than topsoil. Gravel keeps water from pooling around the metal and gives a cleaner finish. Leave the very top of the anchor head slightly exposed or flush with the gravel so you can inspect and retighten it later if needed.
If the ground is extremely soft or boggy, I would upgrade the installation in one of two ways. The first is to use longer helical piles and install two anchors per leg, with a small concrete collar around the top of each pile. The second is to dig post holes 24 to 36 inches deep, flare the bottom of each hole to create a wider bearing surface, and pour concrete piers with embedded anchor bolts. This works, but it is more labor-intensive and can still settle if the bottom of the hole is not stable. For most park bench installations in soft soil, helical anchors give the best balance of low mess, strong holding power, and adjustability.
A few things I would avoid: do not just push the legs into soft soil, do not use short 12-inch ground spikes, and do not set the bench on loose mulch or uncompacted topsoil. Also, before digging or driving anchors, call your local utility locating service to check for buried lines.
This approach has held up well for me in sandy, loamy, and even wet clay areas. The bench stays level much longer, it does not rock when people sit down, and the anchors resist both settling and lateral movement.