plywood

I am thinking about using 3/4" plywood from lowes to make my 4X4's portable and strong. I know we are not supposed to use "treated" wood, and this plywood says it's pressure treated, which sounds ok. But under the specifications, it says it's treated with "ACQ - Alkaline Copper Quat" as part of the process. I looked it up, and it's definitely a chemical use...I want this to be organic...any thoughts?

if you want organic I WOULDNT USE IT ask if they have some that not treated

According to Miles McEvoy, who works in organic certification with the
Washington State Department of Agriculture, no pressure-treated wood is
allowed in soils used to grow organic food. If you want to meet this
high standard, choose a different material. Studies have shown that
arsenic from wood treated with CCA leaches into the soil and that
copper, although much less toxic, leaches from ACQ and copper boron
azole (CBA, a variant of CA-B).

Source: http://www.finegardening.com/how-to/articles/are-pressure-treated-woods-safe-in-garden-beds.aspx

CCA shouldn't be available anymore, unless you get some used wood from an old building. I don't think it's been made since the mid-80's(and even though it was found to be toxic, the gov't allowed any CCA wood in stock to be sold, just not made anymore).

ACQ is safe(so far) for veggie gardening(if it wasn't, I'd think we'd have heard something by now). It's not allowed in organic gardening since ACQ is a non-organic fungicide and pesticide which can leach into the soil(and theoretically kill the good fungi and the good bugs too). Though I wouldn't personally use ACQ(or any other wood that is treated against rotting and insects) simply because I like my soil to be healthy and not semi-sterile.

Form the research I have done there has been a change on what pressure treated wood used to be and what is currently available at the box stores.

Talking to a man, who is a long time employee of 84 Lumber, he told me a radical change occured in 2003 when the EPA changes what components were allowed into treated lumber. Aparently this has been an ongoing process, reducing the ammount of chemicals in pressure treated wood, so today this wood has very few chemicals in it and its prime purpose it to keep it straight for a couple of years.

I told him I was making a SFG and asked him about the concerns of chemicals, he said just line it but there was not much to worry about. Then we walked outside and he pointed to a newly built fence someone was building out of the new pressure treated lumber and pointed out how it was bowing already!!

I puchased all my pressure treated lumber for my SFG and lined it with plastic on the inside....

Music Teacher wrote:I am thinking about using 3/4" plywood from lowes to make my 4X4's portable and strong. I know we are not supposed to use "treated" wood, and this plywood says it's pressure treated, which sounds ok. But under the specifications, it says it's treated with "ACQ - Alkaline Copper Quat" as part of the process. I looked it up, and it's definitely a chemical use...I want this to be organic...any thoughts?

I struggled with this when building my SFG boxes. I decided on using cedar 2 by 6's. In the grand scheme of things, I wasn't willing to risk my health on a couple hundred extra bucks. There may be no risk now with newer pressure treated wood, but why even take the chance. Keep in mind, I am not 100% organic and do use chemical pesticides and fertilizers sometimes. You will find that everyone has an opinion on this topic and there is no right answer here.

1. treated wood is over rated. Treated wood does rot with time. Whatever chemicals it has in it WILL leach into the soil, sooner or later.

2. treated wood purchased at the box stores is usually wet. Whatever is wet will leach into the soil immediately.

3. My landfill fines me $1000 per occurence for any treated wood disposed of in other than the treated wood container. It also charges me a premium to dispose of it safely.

4. You have to use safety precautions so you don't breath in any treated wood sawdust.

5. I have not seen a single agricultural authority who suggests treated wood for use in gardens. Those who address the issue warn against it.

In my not so humble opinion, treated wood should not be used by any gardener. It should not be used around children or animals. There are a number of alternatives to treated wood for use in our boxes: pine is the cheapest, and if purchased in two inch width boards, should last a long time; next come cedar and redwood, both expensive, but will last a very long time.

In a recent discussion on the forum, the consensus seemed to be that 2" thick pine provided the best value for the money vs longevity. That said, my personal preference is for 1" thick rough sawn cedar.

Tom

TP, please substantiate your opinions that pressure treated wood is harmful to the end user. I find many opinions, but I can't find the scientific testing that was performed to support them.

januaryX wrote:TP, please substantiate your opinions that pressure treated wood is harmful to the end user. I find many opinions, but I can't find the scientific testing that was performed to support them.

I suggest the following thread be read from start to finish.

https://squarefoot.forumotion.com/t9808-lining-boxees-with-polyurethane-spray

There are probably many other threads that address the question.

A good overview of the question can be found here:

http://www.finegardening.com/design/articles/pressure-treated-wood-in-beds.aspx

http://www.ecologycenter.org/factsheets/pressure-treated_wood.html

An article on the subject with citations of sources is given here:

http://anrcatalog.ucdavis.edu/pdf/8128.pdf

As for my other assertions, they are based on direct observation. Three years ago, we purchased a house in New Jersey where the previous owners had used significant quantities of preserved wood in garden edgings and elsewhere. They had all rotted in place. We transported all our treated wood to our local landfill at considerable expense for disposal. Again, that treated wood is wet at time of purchase can be directly observed by going to your local box store. The various warnings about using treated wood are widely available on the internet. A simple Google search should suffice.

Bottom line: leachate from treated wood is a permanent contaminant of the soil.

Sawdust and shavings from treated wood accellerate the leaching process. According to the warnings, you can't breathe it, eat it or touch it without adverse consequences.

Other solutions present esthetically and biologically superior choices for border edgings. We replaced our driveway plant edgings with Belgian block for example. We use pine & cedar for our SFG boxes, locust for fence posts.

One more thing: I have a brother-in-law with recurring cancer. He's been eating veggies out of a couple of beds that have been lined with pressure treated wood that is now some 20 years old. Is there a connection between his cancer and the leachate from the treated wood? I don't know and can't prove it one way or another.

The whole organic movement started a long time before any of the modern scientific studies proved Rodale and his followers correct. When pressed, Rodale could only say that his veggies tasted better - that was irrefutable. The rest was based on the limited knowledge available at the time and reasoning tested by experience. Today we know a lot more about the benefits of organically grown meat and vegetables and the dangers of the alternatives. That said, there continues to be a general absence of corporate and political responsibility and ability to do the right thing. But that's another soapbox.

Tom

Yes Tom, my wife & I just joined a health club sorta thing based on food. After looking through their material, it seems as though we pretty much have our food system and things that we use daily,,,,,,just pretty much have it screwed up. Very hard to live in the environment that has been created for us to live in. From milk, to foods tainted with chemicals, to the corn feed beef, to genetic modified crops, to etc. etc. etc. In order to live outside of all this is impossible, but I believe one should try to limit the intake or use of as much of this stuff when and where he can. I believe I would not use the pressure treated plywood in my garden. That's just my opinion.

I would say the majority of SFGers do not use presure treated lumber but many of the sites I have visited in this area refer back to the old pressure treated lumber we used to have for generations. I will agree this lumber had a LOT of bad chemicals in regard to raised beds.

Since 2003 the EPA took out many of the most toxic elements and what is left now is mainly copper elements. So I line my bed both sides.

Mel says to keep away from this lumber though...........

Just to be clear, I was always going to use untreated for the sides. I was confused about why the only plywood choices for the bottom seemed to be treated. I am going to call around and hunt down some untreated plywood, if such a thing exists. Thanks!

We are building all new boxes this year with Trex decking. It is a composite wood/plastic product that uses no chemicals in the manufacturing process. The manufacturer verified no harmful chemicals are used even in the sealant and it is food safe and free from leaching. The other nice thing is they use 70% of our recycled plastic bags to make the product. It comes in some great colors, too.

Not all composite products are the same. Many of them use harmful chemicals to manufacturer and finish so be brand wary.

I used Trex for my first two SFG boxes. An observation:

Trex is very heavy, and sunk into the ground a bit over the course of a year. Putting the squares together is a two person job. The boards I bought (on sale, of course) were not wide enough. I would have been better off buying an 8 inch wide board. I also would have been better off using the Strong Tie bracket rather than the L brackets I used. Other than that, they performed as advertised.

Hey Tom, Did you use a weed barrier? If so was it just inside or was the box sitting on top of a full piece? I am just wondering if that would help with the sinking. Since we are going to mulch around the boxes we were going to cover that entire part of the yard with weed barrier and just lay everything on top. Sinking is an issue here too, any paver stone I isntalled in the last year is already down an inch or two.

Thanks for the tip!

Yes, we used a weed barrier and rested the box frame on top of it. As you can see by the photo, the frame sunk into the ground approximately 50% of the board width. I was quite surprised when I pulled this frame up a couple of weeks ago. My guess is that to avoid that in the future, I would have to put down a support wider than the Trex width to spread the weight. Weed barriers are rated according to their durability, which I did not know when I bought my weed barrier. So it probably deterioriated over the course of the year and would not have provided any support beyond the first year. I replaced this frame with a cedar box. I'll reuse this Trex frame elsewhere in the garden.

Tom

I think there is a fine distinction here between the "lumber" which is the sideboards and the "plywood" which is the bottom. When we shop, it's normally much easier to find and understand "treated vs. untreated" in the lumber area, than in the plywood area. I think the question is about if there is such a thing as non-treated plywood and what to ask for and where to find it. On page 58 of ANSFG Mel says to use "plywood sheeting". Is that what we ask for? Does some "plywood sheeting" come treated and some not?

To the OP - Boffer uses hardware cloth for the bottom of his TTs as an alternative to plywood. There is more info in this post:
https://squarefoot.forumotion.com/t297-building-a-table-top-sfgsome-ideas

There are multiple grades of plywood. One of these is pressure treated plywood.

Plywood meant for interior placement will deconstruct rather rapidly if placed outdoors, as will chipboard (an eternally inferior product, IMHO). So I would look for exterior grade plywood, but not treated.

Do you have to put a plywood bottom on your bed boxes? I would think you are limiting how far down your roots of your veggies could grow. I didn't put any bottoms on mine. I just built my boxes, put them directly on the grass, filled with dirt, and never looked back. This is the first I have heard of someone wanting to put a plywood bottom on their box. I have heard of putting mesh or wire to prevent burrowing animals, but never solid wood.

Just curious.

I would want a bottom for a table top box. I have one such at my elbow in my office, just one square foot. But anything on the ground, I personally don't see the need for the expense.

Many veggies have extraordinary root depth. I see nothing to be gained by limiting that. That's why I'm liking the idea of cardboard for a weedbarrier. By the time the veggie roots are thinking about putting down long roots, the cardboard, having fulfilled its weed barrier function, should have rotted.

Tom

tomperrin wrote:I would want a bottom for a table top box. I have one such at my elbow in my office, just one square foot. But anything on the ground, I personally don't see the need for the expense.

Many veggies have extraordinary root depth. I see nothing to be gained by limiting that. That's why I'm liking the idea of cardboard for a weedbarrier. By the time the veggie roots are thinking about putting down long roots, the cardboard, having fulfilled its weed barrier function, should have rotted.

Tom

Ohhh, that is it. Building a table top box above ground. That makes sense to me now. I was making the assumption that the boxes would be straight on the ground. Thanks.

Hi Georgia!
One of the best parts about Mels updated method is that when you use a good Mels mix, the roots never have to go outside the 6 in. depth. The only reason they spread is to look for water and nutrition, but since everything is right there in the six inches they stay put and happy. People put bottoms on their boxes for different reasons, for example if they are going to be raised or movable. If you haven't read the All New SFG book, grab a copy off of the foundation website It's a quick read with lots of pictures, and very inspiring!

And Tom,

My husband was floored when he saw your photo today. We are going to use the weed cloth that Mel has on the website. I sampled a piece last weekend and it is very thick and sturdy. I like your idea of supporting the sides in addition to a less degradable weed barrier. Even if there were just some simple 4x4x1 blocks under each corner it may help. What size are your finished boxes?

Music Teacher wanted to make the boxes portable, thus the bottom.

On page 68 of ANSFG book, Mel shows the method of installing plywood bottoms for boxes and discusses the thickness needed for each size. ie 2x2, or anything spanning less than 3 ft needs 1/2 inch plywood. For a 4 x 4 he suggests either 5/8 or 3/4 inch and suggests 3/4 inch if you think you will move it often. He also suggests that if you want to rest the boxes on sawhorses or blocks, you need a thicker plywood for unsupported spans. Drainage holes are needed, at least one 1/4 inch hole per square foot as well as another hole in each corner.

Some of us find that it is not necessary or even desired for the plant roots to go down into the dirt. In some areas bad or contaminated soil or horrible weeds or some grasses that cannot be easily killed will try to grow up thru the bottom of your bed if there is no plywood bottom.

MM has all the nutrients needed if you have a 6 inch depth to grow them in. Even tomato plants can grow successfuly in 6 inches of MM. Of course if you have some especially deep rooted crops like carrots, parsnips or potatoes, you might want to make the boxes deeper or add a top hat arrangement to deepen just the squares needed.

These are my first squares shortly after planting (April 17, 2011), the ones in the foreground being made of Trex (4' x 4'), the ones in the background being 8" x 50" x 50", which was the size of wood that I had available. My current batch of new squares run 7" x 49" x 49" using rough cut cedar. The reason for the odd length is that when the boards came to me from the mill they were all a little over 8' long. So I figured why waste the space.

DannDacia - I'll follow your suggestion. I'll use a simple brick placed under each corner dug out so that the square box rests level with the ground. That should be sufficient to stop the sinking due to the heavy weight of the Trex.

As for root depth, I'm too new at this game to have hard core experience with planting in SFG, so I can't pontificate with any authority whatsoever. That said, logic suggests that plants evolved their normal root depths for a reason. As the saying goes, roots are smart, and a lot smarter than I am. So if they are happy with 6 inches, so am I - providing however, that they get a full six inches of soil. The mix that we install in the spring will settle or compact somewhat. So are the plants getting the benefit of the full six inches? I think not, unless we intervene when the soil settles by adding more mix.

The other consideration is that a deeper root depth provides better protection against heat and drought (one reason why good organic farmers tile their fields - the better drainage, the deeper the root will go). Corn is a good example. While here in NJ a lot of farmers irrigate their corn, I suspect that they do it because the subsoil is too poorly drained. The corn does not fully develop what would normally be a 4 foot deep tap root. So the cornfields are, in effect, just an oversized garden that needs to be watered regularly. In my case, I'll let my corn sink its roots as far as they will go. With any luck, the tap roots just might penetrate the clay barrier and provide some natural drainage where I need it most. I'll rotate the corn with sunflowers for the same reason. Sunflower tap roots can reach 9 feet down. When the roots decompose, the water will follow where the roots were. Will any of this work? Dunno. I'll find out when it happens, if it happens.

Bottom line: I think whether or not a root barrier is put down depends on a number of factors: natural and normal depth of root, underlying soil, etc. A root barrier should not be confused with a weed barrier, which is another thing entirely. Unfortunately, a barrier is a barrier, unless it decomposes. We're just lucky that most of what we want to do works just fine in six inches, particularly if we don't let MM dry out. And, MM is designed to retain water. There are probably only a handful of veggies that want a deeper root depth than our statutory six inches. These can be found in the books referenced below.

Sources: Root Depth of Field Crops by John H. Weaver

http://www.soilandhealth.org/01aglibrary/010139fieldcroproots/010139toc.html

Root Dept of Vegetable Crops by John H. Weaver and William E. Bruner

http://www.soilandhealth.org/01aglibrary/010137veg.roots/010137toc.html

My evolving SFG can be found here:

http://www.flickr.com/photos/11987465@N00/sets/72157629083424651/with/6782720807/

Tom

hahaha brainchasm!

Isn't plywood toxic (because of the glues)? If I had to redo my boxes I would try to find the least toxic thing I could. I know plastic also leaches chemicals over time, but there are things you can add to the soil that will eat the toxins (like BioZome). Perhaps that would work with the plywood as well. hmmm...

Oh no, I thought Mel said in his book to use plywood for table top boxes? Help! I'm getting ready to redo them this weekend!