What he said.
toxcrusadr nailed it.

1. If plant roots not penetrating into the native soil is not organic gardening then a lot of us are not organic gardeners since we garden in our native soil, not in raised beds. There is some research that shows plants do not uptake from soils the heavy metal contamination from PT wood, although all plants do uptake small quantities of Arsenic. If the soil we have is contaminated then we are exposed by those contaminants getting on the food we eat, not insde it. Some of the poisons people apply, or have applied, to their lawns and gardens do stick around for many years and mixtures, a synergistic affect, can be worse then the poison itself.
2. How long it takes cardboard to be digested by the soil bacteria depends on how active they are. I have seen cardboard essentially whole 2 or 3 years after being laid on soil that was essentially dead and I have seen cardboard totally digested in a matter of months.
3. Not much. Growth might be stunted or the roots may just travel in a different direction. Root crops are of more concern and you could have deformed carrots, turnips, parsnips, if the soil depth above the cardboard is not quite deep enoguh for what you are growing.
4. Depends on what they are, the soil, the amount of water applied, drainage, and bacterial activity. We are finding that Ma Nature is much better at cleaning up our contaminated soils then we thaught possible, by providing bacteria that digest the junk we put into our soil.
5. More is not better. A single layer of cardboard, or 4 to 6 layers of newspaper, is all that is necessary.

1) Am I being too pedantic in thinking that the roots penetrating the native soil is not considered to be organic gardening, especially with the remote possibility of chemicals from the PT wood posts leaching into the soil and the possibility of residual chemicals in lawn treatments over the years.

len - native soils should be considered to be organic for the purpose of eh exercise at least, in a word don't be concerned about it just concentrate on the job at hand.

2) How long will cardboard take to decompose to the point that roots can penetrate? I usually plan just after May 15th every year. Will it decompose enough by the time the roots grow to the bottom of the container?

len - i prefer news paper it does a better job on the tough weeds like nut grass/sedge, but again if you can get c/board easily use it, nothing much is going to grow up through that and 6"s of garden medium. whether it breaks down over 6 months or 12 months again should not cause you any concerns.

3) What happens to my veggies (tomatoes, cukes, and herbs) if the roots can't penetrate the cardboard this season. Will they die or will their growth just be stunted?

len - so long as you have at least 6"s of medium the vege' roots will be fine as will the plants keep them well mulched up to 8"s thick.

4) How long do lawn treatments stay active in soil?

len - don't use any treatments if they have been used then in time they will be all but gone, just build you raised beds which will create a growing zone above all that.

5) How thick of a layer of cardboard are we talking? I say Jon's photos and it looked like he had several layers.

len - again for me 20 to 30 pages sometimes 40 pages of newspaper better than cardboard but if you have heaps of cardboard use it and don't be concerned it will disappear and do a job.

so what is done for now is done, move onto the next bed project and take a look see at our presentation, this is all about you doing what you feel will work best for you, nothing is set in cement ie.,. use others ideas as a guide not a recipe.

len

Here is a link that might be useful: lens straw bale garden

thanks all for the advice... i gathered all of the boxes from our move last summer and laid them out (over the beds for now) just to see if I have enough. I'm one shy so no biggie, I'll procure one this week. So basically I'm going to have a double layer of corrugated cardboard (each box will be flattened, not broken down). That should probably be enough. The cardboard is just wide enough to go out three inches beyond the perimeter of the bed frames.

My top soil is being delivered on Thursday. Friday morning the plan is to soak the ground, lay down the cardboard, soak the cardboard, lay the frames on top, drive in 24" nail stakes near two or three corners of each frame, level the frames, attach the frames to the stakes at the appropriate hole with decking screws, then fill each frame with top soil. After that all I have to do is wait 5 more weeks until planting.

If you are having soil delivered you may want to consider purchasing a 'veggie' or 'garden' mix from your supplier, something with a good amount of compost and/or amendments mixed in. It doesn't need to be their premium bedding mix necessarily, but the most popular choice for vegetable gardeners or the middle of the road mix. ~$25-45/cubic yard before delivery from what I've seen.

A great tutorial is given in Jon's videos.

Here is a link that might be useful: Jon E. Hughes Wonderful Garden 3-20-2010

I try to break up the soil and add a layer of composted horse or goat manure before building the beds. Something for the roots to reach for (I don't know if it's true, but I've had pretty good luck so far!)I also use the hardware cloth instead of cardboard because I have gophers from hell who would snack their way right through that cardboard!
Find out if you have gophers! Nancy

not sure if this is clear from your post, but do you plan to smother all the grass within the entire fenced enclosure, or just under the raised beds (since you said "The cardboard is just wide enough to go out three inches beyond the perimeter of the bed frames.") I would get the lawnmower on lowest setting, mow the whole enclosed area, bagging the clippings to keep it from jamming up. Then the cardboard will lay more flush to the ground for smothering the lawn. Then you can cardboard the whole area of the garden. Or maybe you had a different idea? What is the plan for the paths between the beds?

Rachel

Art1, The soil I am having delivered is a premium soil/compost blend. It is call 'All Top'...see link below. Its $32 per cubic yard but its costing me a lot more because delivery is $69 and all I'm getting delivered is 2 cubic yards. The only question I have is how can I verify how fertile it is and whether or not it will need ammendments.

Nancy Jane, no gophers that I'm aware of.

Mustard Seeds, just going to smother the grass under the beds for now. I'll be using my string trimmer to keep the grass/weeds between the beds manageable. If my garden is a success, my plan next year is to eliminate the grass altogether and make paths with some material that is TBD.

Here is a link that might be useful: All Top