Do you mean 2 inch thick by 12 inch wide boards ?
If yes, then I would say it is just fine, b/c the ground itself would have soil underneath.
. My raised beds are just 12" high but i have conditioned the soil under them.So the roots can grow deeper if needed.

Seysonn

thanks S....that is what I thought. Because my soil is clay...I need to dig down and mix in some amendments to make that ground level soil usable/loamy. In my barrel containers...the roots of my maters have gone down nearly 3 feet.

Many are telling me on the other site about the importance of organic matter in the raised bed medium. It sounds important...

"I need to dig down and mix in some amendments to make that ground level soil usable/loamy."

Feelin' energetic, eh? The vast majority of the tomato roots will be in that 11-12 inches of added raised bed soil. Water wise I believe that old dirt is not much different than amended dirt, so those roots will still go down looking for water even if you don't dig. Tomato roots are amazing; not much stops them. Amending efforts will still gradually work their way down, dig or no dig, and will work on the clay too. Be relentless in adding organic matter; it's easy to add too little and hard to add too much.

If you later feel like another six inches is good, just add boards edgewise on top of the 2X12s. Negligible fastening is needed and you can wait until you've built up that one foot of new dirt first.

G...I think that is all good advice! thanks

I used to bend over backwards "amending" my heavy clay soils, using cover crops, double-digging - the whole 9 yards.

Until one year I dug into the ground and found the cover crop I had planted last year perfectly preserved between the layers of cold, gray clay where I had dug it in the year before.

So I went with mulching - because a few years before that, I had a plot in a community garden where we had access to a gigantic pile of hay. I mulched to a depth of over 12" - AFTER the hay had settled - it was the middle of a drought that year and I had the best garden I had ever had, despite having to haul water to the site in milk jugs. Which, btw, were a fairly new innovation at the time, and cost more than buying the milk in cardboard cartons.

Since then I have found that unless you live in slug central, a double layer of broken down brown corrugated cardboard boxes covered by the cheap or free mulch of your choice - even including bagged wood mulches, as long as you avoid the ones that are dyed - and a drip irrigation system leave you with as near to a carefree garden as one could possibly hope for and still be living in the real world. Oh yeah, and not having other people do all the work for you, LOL!

Mulching and measured drip irrigation also, it turns out, encourages earthworms, and that IS just like having other people do all the work for you as far as soil amendments. They aerate, they pull down the lower layers of mulch into the soil as it decomposes, they do all that soil "mixing" that double digging was supposed to do at the expense of back breaking labor. Except worms don't HAVE a backbone and this is what they do naturally.

Don't pull the cardboard up to the base of the plants, instead leave an area clear all the way around the stem for where you will put your emitters (or aim your watering wand if you hand water).

I also habitually plant everything but row crops (like peas) in a bowl-shaped depression to funnel water to the plant roots. I leave more area free around tomatoes because I plant them trench-style - I pluck off all but the top one or two sets of leaves, dig a trench that slopes upwards to where I want the stem to emerge. This encourages root development along the entire stem. I leave that entire area free of the cardboard mulch so the entire stem can easily be watered.

I do pull the top mulch, which is usually wood mulch now that I'm stuck in suburbia, across the trench, but not all the way up to the stem. Leaving that clear eliminates slug damage, though that's not usually been a problem for me.

If you have access to something easily compostable like straw or hay, you can just keep layering it with new mulch every year. Yes, hay has the reputation for being weedy, but you won't much notice that if you keep the mulch deep. Also the cardboard layers help to keep any weeds from rooting well, and the thick mulch makes anything that manages to poke its head above the top very spindly and easy to pull.

Still, you might want to avoid hay when possible because sometimes it can infest your garden with bindweed, the seeds of which can lie dormant in the soil for virtually ever. This is only a problem when you STOP mulching, but there it is. The year I had access to unlimited amounts of hay, there were already much worse things than bindweed in that field, which had been farmed for decades and was thoroughly infested with giant hogweed already.

However in an urban setting I've found that bagged wood mulches work just fine and with the cardboard underlayment, you don't need more than 2" or 3" depth. It will eventually rot, but not in less than several years. You can also often get mulch from yard waste the city has gathered and processed for little or no cash outlay. This is often at least partially composted.

The cardboard lasts 2 years and sometimes more. If you're using a longer term top layer like wood mulch, you can easily pull it back (especially in raised beds) and lay down new cardboard. If you're using something like straw, you can just lay new cardboard on top of last year's mulch when the underlying cardboard has broken down. I'd plan on doing that every 3 years or so. Then cover over with your compostable short term mulch.

Do not use grass clippings as a mulch. They mat easily and will tend to shed water.

You might be tempted to use shredded paper as a mulch. In most parts of the country I advise you not to try that, at least not as a top layer. It, too, tends to compress, mat, and shed water - but worse than that it is usually mostly white paper, reflects too much sun, and keeps the soil not just cool, but unacceptably cold too far into the growing season. Instead I compost it with grass clippings to balance out the high nitrogen from grass clippings.

Mulching with a cardboard underlayment works well with hand watering or drip irrigation. Don't even try it if you are top watering with something like an oscillation lawn sprinkler.

Zen,
Am going to try your cardboard and straw mulch this year in my new garden. I hope the strong Kansas winds in summer don't cause a major problem. I will try to keep the mulch wet to weight it down.

I wholeheartedly agree with your advice NOT to put grass clippings in your garden. We had two early summers with tremendous rains and grass growth about seven years ago, which prompted us to buy a grass catcher for our John Deere mower so I could use the grass clippings from our three mowed acres for mulch. I put it on about 6 inches deep and had the most beautiful gardens that never needed weeding for those two years. I found out in the next few years that my tomatoes were plagued with alternaria blight. Then it got worse. Over the next three years I found that I could no longer grow many other crops....peppers, potatoes, green beans, cantaloupe, watermelon, and even zucchini (!!!) would start out fine and then die after a month or so. My 8000 square foot garden beds were done. I am starting over in a new place this year. Won't ever make that mistake again!