I have seen @tapla say in other places that in a true raised bed you can have 100% organic material. Many places recommend you mix in native soil in different proportions, but I think most of that advice is really applied to an in-ground planting and does not consider the drainage in a raised bed. If you wanted to use an organic mix for a raised bed, would it make sense to get at least 5% of the soil mix as native clay loam soil? Clay seems to have extremely good mineral buffering qualities, so it seems like a small amount would go a long way, in providing plant nutrition in the raised bed.

Depends on how much you want to water. If you use a soilless mix, you'd probably have to water twice a day. I mix clay soil into soilless mix to put in pots. I'm away for work a week at a time, and with some clay in there, they can make it a whole week without watering.

Rubi said: Depends on how much you want to water. If you use a soilless mix, you'd probably have to water twice a day. I mix clay soil into soilless mix to put in pots. I'm away for work a week at a time, and with some clay in there, they can make it a whole week without watering.

The main problem I have seen is that with anything above around 10% clay, the soil hardens up. I want it to remain friable.

How much clay does the clay loam have? My soil has clay and cracks when it's dry, but it's real soil. I think your mix would harden up when the sun dries the surface, but underneath, it would be friable.

Rubi said: How much clay does the clay loam have? My soil has clay and cracks when it's dry, but it's real soil. I think your mix would harden up when the sun dries the surface, but underneath, it would be friable.

I would estimate my soil at 40% clay, 40% silt, and 20% sand. My last UMass soil test did not break this down, which is frustrating. I have found by experiment that more than about 10% clay results in the soil compressing and becoming hard.

It is probably the case that a soil with 10% clay can be easily broken up, but as an experiment only I would really like to understand if I could keep the soil highly friable even after it settles, while providing enough clay mineral in the soil to help the plant grow well. I don't know what the right amount is. @tapla has said elsewhere that he wishes he had added more clay into his raised beds.

It would be super interesting if someone set up a line of raised beds with different grades of sandy loam and allowed those to settle. Walking down that line and seeing what percentages of clay and sand do to the final settled soil consistency would be helpful.