No, you cannot.
That is an easy question to answer. But if you want to understand why you cannot just lay pavers on dirt and why you should always prepare a proper base for your pavers, read on.
Why Laying Pavers on Dirt Will Fail
The base preparation of any paver project is the most important part of the project. It is also typically the most labor intensive and time consuming part of the process with the excavation and base preparation. This is usually why people, and some “contractors”, will want to skip this process and move right to installing pavers over dirt. This will no doubt save you money in the short term. But it will be more costly in the long term as you will need to have the pavers picked back up, the jointing compound will be wasted and you will have to clean that jointing material from the side of the pavers adding more labor, the edge restraint may be gone, and all labor involved in the installation of the pavers on dirt will have been wasted. And then you are back to zero with no project installed and needing to complete the project properly.
If you install pavers on dirt, it will fail. It wont take long either. Having a proper base prepared for your pavers provides a foundation for your project to sit on. The base material should be compacted to avoid settling, geotextile to separate the subsoil from the base material, and a compacted subsoil.
Water is the destroyer of infrastructure. And dirt will retain that water, not allowing it to drain. That water will cause your pavement to fail in due time. The first thing that will fail will likely be the jointing compound. Without proper drainage, jointing compounds like polymeric sand will not cure properly and will eventually become loose and break apart. Your pavers may also experience bad efflorescence. This is a white powdery residue that appears on the surface of concrete. It occurs when water is evaporated through the surface of the paver dissolving minerals within the concrete and depositing them on the surface. With more water below the pavers because of the retention of water through the dirt, the more efflorescence will be deposited on the surface of the pavers creating unsightliness and the deterioration of your pavers at the bottom.
If you live in a climate where you experience freeze-thaw cycles, you will undoubtably have your paver project fail if you lay directly on dirt. This is once again because of that water retention of dirt versus a draining base material. When that water freezes during a freeze cycle, it will expand. This water will put pressure from the bottom of the pavers and begin heaving them. This will be throughout the entire project and will cause tripping hazards and further unsightliness.
Interlocking pavers interlock which is what gives them their strength as a pavement. This interlock in one aspect comes from the appropriate aggregate in the bedding layer, which is the levelling layer of aggregate directly underneath the pavers, moving up through the joint of the pavers to meet the jointing compound. This is achieved through the compaction of those pavers after they installed and when that jointing compound is being installed so that the pavers are pushed into the bedding layer. Dirt is not the appropriate gradation like the approved aggregates for a bedding layer to provide this interlock. With no interlock achieved with your pavement, you will not have the main attribute of that pavement to withstand traffic on the surface.
How to Lay Pavers On Dirt
If you are adamant on laying your pavers on dirt, we highly suggest you use paver base panels. These will replace your base material and reduce the excavation significantly. However, you do still need to ensure that you are excavating organic material such as topsoil and getting down to a foundational subsoil such as sand, silt, clay, or a mixture of these. Once you achieve that excavation, you can then lay a non-woven geotextile, screed a one inch layer of HPB or 1/4″ clean chip stone, lay your paver base panels, and then lay your pavers on top of these panels. If you dig down and you are digging more than five inches of material before hitting your subsoil, then it likely makes more sense to prepare a traditional or open graded base rather than using these panels. This is because the main benefit of these panels is that they will save you significant excavation, but the tradeoff is that they cost more in materials. If you are already digging the depth required for a traditional or open graded base, the cost-benefit is negligible.
Using a proper base preparation method will ensure the longevity of your paver project rather than installing something that will look okay for a couple of seasons only to become ruined with the passage of time. Especially if you are installing your project in a climate that experiences multiple freeze-thaw cycles. These cycles will ruin your paver project quickly if you are laying pavers on dirt.