Raised Bed Material

mgecaApril 9, 2007

I'm ready to build some raised beds for our vegetable garden. I need some ideas and opinions on materials to use. We want something that will endure the weather, soil moisture in the garden, and ground contact.

We will have four 4'x4' beds about 16-18" high.

Cheapest and in the thickest dimension (2") is treated lumber. I know this was determined to be a health hazard some years ago, but now they say it is environmentally safe. I'm skeptical but it would be perfect. Contaminated beans don't appeal however.

Cedar is attractive but I can only find 1" thick boards, which I feel may bend or buckle with the weight of the soil, even in 4' lengths. Moderately expensive.

Composite "lumber" also is only available in 5/4" thickness and is really costly. We used it a few years ago for a raised bed and had buckling problems with 8' lengths. A design flaw I guess, but still very expensive. And who knows if this stuff leaches anything into the soil.

What can you tell us about good and safe materials for our raised beds? Can you turn us to any place that has design ideas for building what ought to be simple rectangles?

We appreciate all your experience and any help you can give. Thanks.


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I'm not sure where you might be located, but all lumber products, including the composite lumber, should be available in common standard dimensions, the 1 3/4" inch thickness of a 2by being the most common. Buckling or bowing should not be a problem with this thickness for a 4' length.

Arsenic-embedded treated lumber is off the market - other pressure treated products, including the composite lumber products, will pose no problems for a raised bed OR organic veggie growing with regards to the leaching of any chemicals.

So select what you can find locally that will fit your budget - the composite product will arguably last longer than either the PTL, cedar or redwood. Putting the bed together is just a matter of basic carpentry skills. Directions for various methods are easily available online.

    Bookmark   April 9, 2007 at 7:09PM
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saypoint(6b CT)

I built mine out of PT 2x10 lumber, screwed together at the butt-jointed corners, and with angle braces screwed to the inside for a little extra support. Each bed is 4x8 feet. They've been in for three years.

    Bookmark   April 9, 2007 at 9:29PM
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mad_gallica(zone 5 - eastern New York)

Ours are just plain old 2 x 8 pine. Before they were filled, they were whitewashed. They are currently 8 years old, beginning to rot a bit, but they are definitely going to hit the planned lifespan of 10. The price of many building materials has gone sky-high since Katrina. When we built the beds, the lumber was dirt cheap. The galvanized screws to hold it all together was the pricey part.

    Bookmark   April 10, 2007 at 8:18AM
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Just to be persnickety, a 2x piece of lumber is currently 1 1/2" thick. If it is 1 3/4", that means it is pretty old!

(And for those who are wondering, a 2x4 is 3 1/2" deep, a 2x6 is 5 1/2" deep - but a 2x8 is 7 1/4" deep, a 2x10 is 9 1/4" deep, and a 2x12 is 11 1/4" deep...)

    Bookmark   April 10, 2007 at 10:06AM
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Sorry, Irene and everyone - that was a typo!! I do know that a dimensioned 2x4 is 1 1/2" by 3 1/2". Not sure where that came from except that I have a tooth ache that seems to be affecting brain function as well :-)

    Bookmark   April 10, 2007 at 10:14AM
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bindersbee(6a UT)

I used Trex for my raised beds. I made 2x4 posts at the corner that are sunken into the ground and spaced the posts every 4 feet or so to keep the material from bowing. I purchased my Trex as scraps (it does come in 1" thicknesses) that were left over from a project. Most were shorter than 4 feet and I have some seams that I would otherwise not have but for how inexpensively I got it, well worth it. Perhaps you can check with some decking contractors in your area about purchasing scraps?

As for what it leaches into the soil, I know it's safe enough for use on children's playgrounds. Everything that goes into playgrounds must be safe enough for kids to ingest because they will knaw on anything.

    Bookmark   April 10, 2007 at 10:19AM
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There are a lot of factors to consider for raised bed construction. Over the last 30 years I've probably used a dozen different materials.

Climate is a factor. I live in a warm area. Termites are a fact of life here. Untreated wood rots faster than in cold regions and though you might still get 4 to 6 years here with wood, if the termites attact you can lose it in a single season. Plus the insurance guy doesn't much like you to feed the termites close to the house. Frost heave can also be a factor that makes one type of construction better than another.

Soil is a factor. If the underlying soil is good, then a 6 to 8 inch height may work well. If you have clay as I do, 16 inches is about the minimum. Material that is cheap for a 6 inch bed doesn't always do a good job at 16 inches.

How long does it need to last? You might not want something permanent if you plan to move in a few years.
On the other hand if you want permanent, then a permanent material may be cheaper in the long run.

I now live in the last house I plan to own. I have clay. I'm not getting any younger and a few years from now I will no long be able to do the work of building raised beds. But I want to garden for as long as I can. For these reasons I moved up to the gold standard in raised beds - poured concrete. Though the labor and time to construct them is more than other methods, the permanent factor is important to me. The cost of DIY concrete is not that much more than other materials and may even be cheaper. A 16 inch high bed runs about $3 a lf.

    Bookmark   April 10, 2007 at 10:57AM
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We used Trex for the sides of a 12 foot by 4 foot bed last spring, and it is still looking good. No bowing, but they are held in place by every four feet along the length.

I DO NOT recommend using 4x4 composite posts for the pilings. Although they should hold up well, the posts we bought (Menards) are very heavy and are full of metal shards and voids. We went through 4 or 5 drill bits to get the carriange bolts in.

We filled the beds with rotted leaf compost, available for free from our county if you haul it yourself. Except for the rare glass chip or foil scrap it is fine, and hardly sank at all over the past year.

hth, VW

    Bookmark   April 10, 2007 at 11:07AM
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'Sokay, GG! Just couldn't let it pass by, y'know? ;) (And you probably don't want to know that *none* of the recent graduates we've hired have known the dimensions off the top of their head!)

Our last veggie bed we actually did with some huge concrete blocks that our old landscape guy found for us, about 16x16x8? (I'm still not sure where they got them - possibly salvaged from someplace, since they never did charge us for them!) Laid on end, partly buried in the ground - that thing wasn't going anywhere once it was done! That was about the time they were switching out the types of PT wood, so we had been nervous about using it. Now I have to decide what to use for our new veggie bed(s).

    Bookmark   April 10, 2007 at 11:22AM
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haringfan(zone 5, MI)

For those of you using Trex (view_west and bindersbee) or other composite lumber, are you using 1xs or can you find 2xs? What are you using for pilings? 4x4s every 4 feet or just on the corners? Untreated 4x4s for pilings? Or PT?

    Bookmark   April 10, 2007 at 1:24PM
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Thanks for all the great responses. Some issues have been clarified but I need to fine-tune things.

We expect this will be our last house so we do want to make the raised garden as durable as possible. Age is a factor in terms of what can be done now and in the future. We also have clay with a high water table. I will drain it to a certain extent, but ground contact will be a consideration in the materials and soil depth in the bed an important part of the construction.

There also is the issue of the gardener in the household. There must be style as well as substance to this effort--meaning treated lumber is low on her list. It is high on mine given the various dimensions readily available, resistence to bowing, rot etc. Two 2x8 boards will give me the necessary depth (or 2x10 plus 2x8). It appears there will be no chemical problems with the vegetables, but I still a little concerned.

The first choice for a nicer appearance is cedar. I don't mind the cost but it is available only in 1" thickness (3/4" or whatever). If I could find 2x8xwhatever in cedar, my issues would be over.

Trex or composite is available locally only in 5/4x6xwhatever. My wife has found a perfect color for her needs, but this means 3 levels of 4x4' boxes to achieve her design depth and to keep above the clay. A lot of money to build the four boxes and a lot of extra effort.

I live in a small city north of Pittsburgh, Pa and we have the big box stores--the above lumber is what I have found in them. I am trying to find other sources--especially for 2x8 cedar.

Here are my follow-up questions. Do any of you use cedar (I think redwood is alien here). Has anyone found 2x8 cedar? Do you think so-called 1" boards 4' long will bow or need stakes (no problem to do), or should I hold out for 2x8? Has anyone stained or otherwise "beautified" pressure treated and how did it work out? Would lining the inside of the boxes (not the ground) with surplus rubber pond liner as insurance be overkill with treated wood?

Sorry for the long post and for repeating some from my original but I only have the energy to do it once--at least I think I have it!

Looking foreward to a final sorting our and decision making, with your help. Thanks.

    Bookmark   April 10, 2007 at 1:41PM
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harleysilo(7 Roswell,GA)

Why not form up and pour concrete?

    Bookmark   April 10, 2007 at 3:28PM
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Think of structure, then style. They don't have to be the same material. This is true whether you go with wood or concrete.

Concrete can be stained, veneered with stone, tile, or wood.

Wood can have a strong structural material covered with a thin wood veneer. Keep in mind that wood naturally ages to a light grey. To keep that beautiful wood color requires a finish that has to be redone from time to time. You might look at building the box of 2x lumber and covering it with the thin red cedar made for closets. The big box stores should have everything you need.

    Bookmark   April 10, 2007 at 3:57PM
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With a few phone calls I have found a source of 2x8x8 cedar boards. Special order that takes 4-5 days. Only unknown until tomorrow is the price. As a couple people said, do what you want and bear the price--this needs to last.

One of our problems is that we have no vehicular access to much of our rear yard despite streets on three side and a challenging access when moving heavy loads.

Concrete is an interesting idea and colored concrete is attractive. Wouldn't the footing for the boxes have to be fairly deep in a Zone 5 with heavy groundwater, increasing the yards needed?

The boxes will be straight forward; bracing decided after they are set in place. Maybe clear coat.

The comments about style and substance/form and function should be kept in mind for most endeavors outside and in. My wife sees color and harmony and balance in her visions of the garden. It never is so clear to me until it is done.

Changes will come but hopefully not involving the material for the beds!

Any other thoughts are welcome--you all have gotten me going in the right direction. Thanks.

    Bookmark   April 10, 2007 at 5:15PM
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Well, since you want it to look nice for a long time, you probably would want at least a trench footing down to frost depth. Depending on how high the wall is, a footing would probably be advisable, since you'll have some unequal pressure due to it being a raised bed. But, I wouldn't think it would need to be huge, since you are talking about a 16" difference in grade. (I don't know what frost depth is considered in PA, but it should be easy to find out.)

    Bookmark   April 10, 2007 at 5:30PM
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I have a question that this great thread just almost answered:) Very informative for someone working with raised beds.

Next spring my husband and I want to grow squash in raised beds on the very far end of our property. The 'soil' up there is hardpan clay. Nothing will grow up there except Virginia Creeper but I would like to utilize some of that space with a raised bed instead. My question is this: if we build a bed to put back there how tall should it be to accommodate squash (zucchini, crookneck)? I'm willing to make it up to 2' tall if that's what it takes to accomodate those veggies.

Thank you.


    Bookmark   August 23, 2007 at 12:45PM
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I can only relate my experience and observations--others will join in with the plant expertise I imagine.

We built four 4'x4' square raised boxes. The depth up to a sit-on-it, put-tools-on-it lip is about 20" The area is wet clay at the base of a slope. I installed a 4" perforated drain pipe at the toe of the slope to a homemade cistern, hoping to create a little more depth for roots. The 20" was just a guess. We purchased good quality loam with some fine gravel for drainage and used about 4 yards to fill the boxes (never realized all the 4s involved).

One box was devoted to squash, zucchini etc with great results--too much of everything, fast and healthy.

In my opinion, the boxes are too small and get crowded easily--altho my wife surely overplanted! But they gave us a look and a fit and an ease of working in them that suits us just fine.

If you can determine an optimum depth for the plant roots I should think you could find the depth you need over the native hard clay soil. You probably should give some thought to drainage at the bottom since the clay will not allow much infiltration.

Guesswork with good results for our location. Good luck - Mike

    Bookmark   August 23, 2007 at 9:40PM
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Thank you Mike. That's very helpful. Going to show your post to my husband as well. Reading about the experiences of people here is just what I need.


    Bookmark   August 23, 2007 at 11:11PM
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You're welcome and hope it helps. I have another thought for your consideration. Since your hard clay soil won't infiltrate very fast, there is a risk of excess water from watering or rain building up in your planting soil. But once it does start to infiltrate, the wet clay soil will hold water that can wick up into your garden soil. Perhaps it will get too wet for your root system.

You might consider a bed of course gravel (I like pond gravel from HD because it is rounded from water activity in the past) in the bottom of the raised bed. If you dug down a couple of inches or so and filled the hole beneath the bed it would be good also.

Then make some "weep holes" around the base of your raised bed. Just drill a line of maybe 1/2" holes all around the bed, maybe an inch above ground level. Fill the bed with the coarse gravel a bit above the weep holes then install the garden soil. This way, water will drain both to the the underlying soil and out the holes. Should help any water problem that might occur. Just clear the weep holes from time to time if necessary.

This is an adaptation of centuries-old drainage in fortifications, castles and the like. The only real extra work is hauling in the gravel.

I do tend to over-design, make mistakes, but doing it once before you have two feet of garden soil is easier than doing it later.

Good luck - Mike

    Bookmark   August 26, 2007 at 12:48PM
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Wow, great information!

We put in a raised bed in the spring. I hunted high and low for 2" cedar, with no luck. Ended up using mail ordered composite lumber 2" x 6" x 4' long. It wasn't the cheapest option, but it was so easy to assemble for someone with no carpentry skills at all.

With the corner stakes that are used with it, I can add more height if in the future - for easier access without bending as much.

I'm just about to place another order and put in a second bed this fall. I overplanted the first bed and it turned into a wonderful jungle.

    Bookmark   September 2, 2007 at 10:33PM
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We're looking at making a second vegetable garden, but most of the "raising" has been done for us. We just finished a new garage, and when the old one is torn down three sides of the concrete footing comprise three sides of the "form" for the raised garden....a space about 22' x 42 ' which will be subdivided into smaller beds.

For closing off the open side, I have some old -but still quite intact- railroad ties about 6 x 6 x 9 feet long, which I salvaged from a multi-level parking lot retaining wall that was being torn down. The big problem with the ties is moving them, since they're quite a load.

On the downhill side, I plan to use a post-hole digger to make a series of holes inside the footing (the long 42' side) of the former garage, and use some flexible perforated drain pipe I have to ensure that the whole thing "weeps" or drains properly.

My largest area of concern is what remains inside the former garage, which will have to be built up into soil. It's a mix of dirt, with some gravel, and the detritus that might be expected to accumulate in a garage that was built in 1953.

    Bookmark   September 6, 2007 at 7:28AM
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rico - your setting has a lot of possibilities but maybe some serious problems. And wow, what a lot of soil to put in. If the old railroad ties are creosote treated you will get significant and bad soil contamination. The use of creosote is severly restricted by law now.

The former garage floor will have lots of oils, greases, anti-freeze, salts, you name it, that could present a problem. Is it concrete or dirt?

Are you planning a checkerboard pattern of beds with aisles? Maybe the railroad tie end can be eliminated for access, little storage bays, maybe even a low cold frame or two. Hopefully others can give you better insight into treating the garage floor.

How high is the existing foundation wall, how deep do you plan to make the beds?

Sounds like a great idea that just needs a little more germinating.

    Bookmark   September 6, 2007 at 9:53AM
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To "mgeca," I plan to address the problem of the amount of soil required by a "strip" approach, dividing the entire area into separate beds that will be cultivated successively, certainly not all the first year. We have a conventional garden that will sustain us quite nicely as we bring the new one on line.

The railroad ties are indeed creosote treated, but there's creosote and creosote. This is not the "old" creosote, which was far more volatile and dangerous. Moreover, these ties are 30 years old at a minimum, and though they're still quite solid, I expect no problem from any of the product they've been treated with leaching into the soil.

The floor is dirt, with an admixture of some gravel. The structure has been there for around 55 years, of which we've lived here the past 17. I'm pretty confident that there's not much that's soaked into the floor during our tenure. I have given some thought to what automotive or other chemicals or their residue might be present in the dirt from the 38 years before that, but after cleaning the place out, I plan to build soil in that area without too much regard for that. We'll see what happens.

Your idea of a checkerboard pattern of beds is an excellent one, and I may elect to forego the ties on the open side. However, if I do that I must do something about the problem that led to the construction of a new garage in the first place, which is the "downhill" position of the old garage. A large driveway / turnaround exists directly opposite the open side, and in a heavy rain, water would flow into the garage, in some cases to a depth of 6 inches in the back. I may resort to incorporating a drainage trench across the open side.

The existing concrete footing is about 6-8 inches high on the inside, perhaps 12-14 inches on the outside. These figures are naturally not completely uniform around all three sides.

    Bookmark   September 6, 2007 at 3:12PM
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We built two 4x8 raised beds from cedar deck planks salvaged from a neighbor who was redoing his deck. I used 2' 4x4 posts in the inside corners to add stability. To deal with bowing along the 8' length I sunk a few of the old 2x2 deck spindles into the ground on the inside and screwed the boards to them. The only thing I paid for was the screws. The old wood should hold for many years and the aged look fits in perfectly with the rest of the yard.

Reduce, Reuse, Recycle...

    Bookmark   September 7, 2007 at 10:15AM
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I am in the process of building with horizontal TREX boards. My corners I am using 4x4 treated lumber however I am placing in a vinyl sleeve that will extend deep into the groung beyond the actual lumber. I am sinking the corners below so that they will not be seen. Every two to three feet I am going to do the same along the long end to stabilize. I plan on this being there forever. No foo-foo top rail dressing will be added to these vegetable beds; they will be simple boxes nested in a front yard done completely in flagstone and gravel.

    Bookmark   February 28, 2011 at 12:22PM
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smwtlr6(Puget Sound)

Would like to hear how Trex beds are performing over time.

    Bookmark   March 9, 2012 at 3:33PM
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