Unless you can dig down and remove that fabric and eliminate all the problems it can cause then yes, I'd definitely vote for deeper. 12-18" total at least. You'll be amazed at the improvement in results.

Dave

Agree with Dave. Notice he said at least.

18 is the min. Tomatoes and beets go down to 4 feet, and they need it. But if the fabric is porous, probably some feeder roots found the holes and went under. The attached website contains all you need to know.

Here is a link that might be useful: http://www.soilandhealth.org/01aglibrary/010137veg.roots/010137toc.html

18 inches should be alright since fertilizers and other nutrients (minerals etc.) stay around from top surface to 18 inches depth.Water also will be well distributed in the range of this depth to provide uniform supply.There is no need to remove fabric if it is at the depth of 18 inches or so.

Thanks all for the advice. The fabric is porous as water can go through it. Of course, that presents another problem in that the water can go through but roots may not be able to go through as easily. This was the first year we grew corn (we dabbled a bit the year before but I don't count that) and while we actually got a pretty good corn crop it looked like on several of the stalks the corn roots were trying to push the plant out of the grown. I wonder if this was a lack of depth or if that's something corn naturally does. A final note about depth, we have significant wind problems and for the second year we lost our broccoli from wind. Around each of the raised beds we installed a plexiglass shield above the bed's wood base. But, we only have soil to a little below the wood base so it sounds like we need to pull off the plexiglass (which is no big deal), extend the base upwards to 18" or so, add to the soil and then reinstall the plexiglass. On top of the plexiglass we had a row cover on most of the beds so it made the garden look like a terrarium. Again, thanks to all for your advice.