Raised Bed Question: 8" or 12"

[angelique]

Hi All,

I need advice on deciding whether to use 8" or 12" high wood for raised beds. The soil that I have is a hard clay. Year years ago, I added a couple of inches of top soil from the nursery. The next year, I added about 3 inches of compost. To date, I haven't used this area for gardening. I was able to get my tiller about a foot down without any problems. I definitely looks better than before. I have a small Honda tiller that cannot go much further down. I also know that there is drainage pipe that is sort of shallow (definitely under two feet deep).

Anyhow, based on this information, will I be okay with 8 inch raised beds, or should I fork out the money for the 12"? I plan on using these raised beds for tomatoes, herbs (annuals) and possibly other veggies. Because weeds have not been a factor, I plan on incorporating the soil below with compost from a local nursery. This should solve my soil problem.

Additionally, I would like to know what is considered a good price for lumber. At HD, the 8' Redwood raised bed lumber is 17 dollars; 12' is 27 dollars. I called a couple small lumber yards. Their prices seem to be pretty close to HD's.

Thanks for your help.

Cheers,

Angelique

[TomatoDon]

Hi A,

The deeper the better. Mine beds are 10" deep and already extablished, and I wish now I had dug down a few more inches. If you could do that I would. I would suggest the 12 " material.

I went with treated lumber. A university study found none of the preservatives leaching into the roots or plants. Yet, I lined the lumber with visquine for double protection.

Don

[Catntree]

You could have a special bed for herbs and other shallow-rooted crops, but for tomatoes and the like you would want 12". 2 feet depth of workable soil would be a good goal, if you can do that.

[cthomato]

I have hard clay soil too. Last year I put in a 12" raised bed (redwood) and amended the 12" of soil below. The results were well worth it. I paid a bit more for the wider boards but they should last years. So I say go for 12" beds, you won't be sorry.

Chris

[travis]

"I went with treated lumber. A university study found none of the preservatives leaching into the roots or plants. Yet, I lined the lumber with visquine for double protection." [Don]

Don,

That's very interesting in light of all the controversy about using treated lumber.

Could you kindly reference or link that study? I'd love to have that info.

PV

[angelique]

Hi Papa Vic,

A local lumber yard gave me the same info. I realized that it is his job to sell lumber, so I pleasantly heard him out. He told me, "We remove the arsenic and other poisonous chemicals before we sell it to you". Hmmm. No that makes me feel safe. Am I going to use treated lumber based on the sales rep info., NO WAY. I really would like to see a study regarding treated wood and vegetable gardening. If anyone has any information, please share.

[MsCowpea]

Here is a very good link concerning the use of pressure treated wood in the garden.

Bare in mind though that CCA PT wood is no longer available anyway to the average consumer due to the concern of , not arsenic leaching, but that children may touch the wood (ie playground set, etc) and then touch their mouths. I believe the phase out was completed in 2004 or 2005???

Wood purchased in Home Depot, Lowes, etc. is ACQ treated.

http://www.taunton.com/finegardening/pages/g00028.asp

[markferon]

i go with 12 ft' long and 1 ft width.

[TomatoDon]

Papa Vic,

Sorry, I didn't see your question till now. The study I'm thinking of was done at the University of Oklahoma, I think. I found it looking up sites about raised bed gardening.

I'll see if I can find the link. I saw another good one posted here about it.

Don

[TomatoDon]

Papa Vic,

Here is another link. It just briefly mentions the U of O study. I'll look for more.

http://www.frugalfolks.com/Members/f...ng.pdf#search=

Don

[valereee]

I'm making some raised beds out of Trex this year. My local lumberyard decided to stop carrying the 2 x 10s, so they sold me their remaining stock at half price, which was $27 each for eleven 12-foot boards. I was thrilled, as I've got two beds made from untreated 1 x 12s and they are deteriorating fast. One is about six years old and needs to be replaced this year. The other was built last year and already looks weathered. I figure I'll be handing Trex raised beds down to my grandkids.

I'm going to till some greensand and some mulch into my heavy clay, set the beds down on top, and build the soil in the beds from mostly organics.

Val

[Torquill]

Is there a reason not to use two 6" or 8" boards on top of each other? Two 6" boards would be cheaper than one 12" board, I would think. Just make sure the stakes anchoring the boards are high enough to anchor both boards well.

--Alison
who hasn't built raised beds, and is therefore just doing thought experiments... beware of the mad mental scientist.

[TomatoDon]

Yes, you can add another stack on top, but it's not necessary. When you build yours, just dig out an extra 12 inches at the bottom. I wish I had. You then have the 12-24 inches of tilth and compost you need, plus better moisture and temperature balance.

Don

[TomatoDon]

Well, you do have a good point there, John. With heavy clay, and poor drained soil, it can cause problems. Maybe we should all top stack our beds and add more soilless mix!

Don

[landarc]

Angelique,

We used raised beds for years in the flower and plant business and rarely used beds more than 12" in depth. I would think that you would be doing fine with either a 8" or 12" depth. Also, we never dug deeper than the bed depth. There was a reason for that, but, I do not know what it was. In fact, my dad's beds were 18" deep, but raised another 12" above existing grade so that there was no ground contact.

As for redwood or p.t. fir, we used only redwood 1x6 stock and 4x posts to good effect. In fact, many of the beds were 60 to 70 years old and many had only sporadic repairs performed. The used of pressure treated fir is generally advisable where structural integrity is critical (structures, foundations, walls etc...) and the inherent superior strength of fir is preferable. In my experience, in the last 10 or so years, the quality of redwood (not so good) and the newer pressure treatment techniques have served to lessen rot resistance across the board. In terms of ground contact, I would just go with redwood, the unkown risks of added chemicals with unkown levels of persistance in the landscape would guide me in that direction.