I want to do a raised garden, what goes under the soil?

Absolutely! You may think about using plastic sheeting, like you would use as a drop cloth from any hardware store. We used that along with garden mix from the local dirt yard on top and worked beautifully. We used 2x4 for the bed frame stacked 2 high. Made a wonderful garden!

We didn't use plastic sheeting, but an organic landscape cloth followed by newspapers then organic garden soil purchased in bulk.

Either will work, just depends if you are afraid of plastic or not.

Landscape fabric ,either plastic or fabric will work.Keep in mine you need to double layer it.

I've used newspaper, three or four sheets thick. That eventually decomposes and can be mixed in with your soil. I've also used landscape fabric. Both work very well.

If you have aggressive local plants (like the burmuda that fills in around here) you will want a longer term landscape fabric to keep out grasses from the nearby areas. They are not terribly expensive, and available from home and garden centers and even discounters like Walmart. Go with fabric rather than plastic for durability. Use two layers, as suggested elsewhere. Have fun with the project!

I just used cardboard-broken down cardboard boxes. Remember to remove the tape on the boxes before putting down the dirt. Just one layer over all the bottom of the bed before the dirt.

If you are using them for vegetables and such you would need only soil I grew my vegetables like this and did not have a problem I did mix in manure with the soil