I just built this spiffy raised bed for a small kitchen garden. I am toying with other more permie planting areas elsewhere, but this is right next to our deck and house so must look nice to my wife. I used non-treated dimensional pine so I could match the lines and angles of our deck. I have now spent many hours researching what I can do to place a barrier between the wood and soil so that:
1. I can stain/paint it to match the deck (it may be toxic gic); and,
2. I don't have to rebuild it in 2-3 years
Apparently, every potential solution will poison you or make it rot faster, so most people just plan to rebuild it ever couple of years. I was considering sheets of food grade plastic, but apparently that just holds moisture closer to the wood and accelerates rotting. This reminded me of a product I used years ago called Delta-FL. It is a dimpled plastic subfloor that creates an air-tight, 5/16" (8mm) vapor barrier between your finished floor and basement concrete. The air gap allows the vapor to equalize without condensing. Would this not also work between the soil and boards of the raised bed, allowing the wood exterior to be painted and extend its life?
The stuff worked great for my basement project and I still have a half roll of it left that I have been tripping over it for 5 years. It's strong. The MSDS tells me it's made of HDPE, which I believe is one of the more stable plastics used for food grade containers. I understand that HDPE is recommended over PVC for aquaponics applications because it does not leach.
This seems like a slam dunk to me. What might I be missing? Maybe not all HDPE is created equal? Maybe there are additional pigments or something that may not be good for you? The brochure says it's "non-toxic, non-polluting", but does not call it "food grade" for obvious reasons. They now have it at the big box stores but you can get it cheaper directly from the company at $0.60/sq ft.
Nice raised beds man! Those look good. Have you considered linseed oil to slow the decay of the wood? Certain boiled linseed oils can contain metals that may leech into your soil, but there is a brand called Allback that has an organic linseed oil for treating wood. That or tung oil may be an option. I believe your thoughts on plastic sheeting holding moisture to be right and that would accelerate the rot. If when they do start to rot (all woods will rot eventually of course) and you choose to rebuild them, perhaps consider a wood that is slow to rot like cedar or cypress. Yes they will cost a lot more than standard pine. I garden in raised beds built from western red cedar, with the oldest being 7 years old now and they appear to be holding up well so far, and I did not treat them with anything. Good luck!
"Study books and observe nature; if they do not agree, throw away the books." ~ William A. Albrecht
I still plan to use the Delta-FL dimpled membrane, but if I can find the organic raw linseed oil locally, I think I'll try to put a coat on the interior. The exterior will be stained/painted to match the deck.
Using cedar or thicker pine is the long game, but I am not going to get that done this year. I thought about just doubling cost/thickness with another layer of 2x10s, but that would be a lot of cuts and screws, and I think the water would still work its way in between the boards and cause the same problems as having a flat membrane tight against them.
I was able to find raw linseed oil locally, so now have a much shinier bed. It's thick, but lays on nicely with a 4" brush. I think most people cut the first coat with turpentine, but I put it on straight. It smells like high school artclass - not at all like the chemical stains I am used to. The brand (http://www.rockmiracle.com/productdetail.asp?cid=&pid=53) does not claim to be organic, but the only ingredient is flaxseed oil. I'm not too worried since I still plan to install the Delta-FL HDPE dimpled membrane between the boards and soil. I hope that this + drainage rocks under the boards + linseed oil coating = a few extra years before rebuilding.
I used about 1/3 of the gallon which was around $36. I think it will be $12 well spent.
Those raised beds look absolutely beautiful. The only thing I don't like about them is I did not build them myself (I am slightly jealous). Linseed oil will definitely work--for a while, but eventually that too will break down. As an alternative, have you considered spray or paint on truck bed liner? You would definitely want this to dry thoroughly before planting, but you can get truckliner paint that will practically armor the inside of your bed, and maybe even paint the tip edge for extra waterproofing. Once the bedliner is dried, it will be impervious to just about anything you throw at it. I would definitely leave the outside as oiled wood as it is absolutely beautiful. Good job!
Those look great! If you are not concerned with all plastics with regard to food production, HDPE will be a great choice. I always find it difficult to give advice on stuff like this as your level of comfort with petroleum / corporations / icky-stuffs always comes into play. We didn't know BPA was bad until we did, and there's always a chance that modern plastics have a similar unknown problem lurking in time. But if you're comfortable using food grade plastic containers, HDPE will do fine.
That being said, from your goals I think wood with a simple finish like you have would also work fine for a very long time. A raised bed is a lot different than a fence post or structural member, and that context is pretty important.
1. Your wood will have 5/6 surfaces exposed to air and 1/6 surface exposed to water. This is way different than something like a fence post where the ratios are reversed. Wood breathes a tremendous amount and this will slow wood rot considerably.
2. Raised beds usually have great drainage, which means the wood won't sit waterlogged.
3. Since it's non-structural, repairs are fairly trivial.
I think people tend to underestimate the lifetime of wood. 2-3 years seems extremely conservative, even for untreated pine. Untreated cedar or redwood that's exposed to air in a non-tropical environment can last for decades.
Quick update for those that could find this useful. The raw linseed oil coating was an interesting/helpful detour, but my main focus is the HDPE liner. Nobody screamed don’t do it, so I did it. I suspect the abundance of plastic in the attached photo may trigger the gag reflex of some higher eco-level permies, and I sincerely apologize for that. Eric - I'm not sure about the truck liner stuff - no idea what's in it which scares me. Kyle - I take your points, particularly regarding toxicities that are currently unknown (or being hidden). I am probably over thinking it and over doing it. I build it in about a day and then say to myself that I don't want to spend another day fixing it in 5 years, so I proceed to spend 2 more days now researching, adding linseed oil, adding a liner, etc. Yes, it makes no sense and is a personal defect, but it's now a sunk cost and at least some growies are going in this weekend! It will be interesting to see how it holds up.
As to the process, the liner went on quickly. It cuts easily with tin snips, and the dimples make it easy keep things lined up and square without too much measuring. I fastened it to the boards with screws 1-2 inches from the top. There are no screws and no holes below that, so no way for water to get to the boards unless it comes from the bottom by way of capillary action, which I assume will happen to some degree. Assuming you are cool with HDPE, I think this liner would work well for any rectangular-ish (or cylindrical-ish) structure where you want to keep water away from untreated boards. I had it laying around, but you would spend around $30-40 to add this to a 12x4’ garden bed, depending on the size roll you bought and waste.
Today I made two more additions that I’m not quite certain about: 1. Waterproof tape at the top to seal the screws and keep water/soil from working behind the liner; 2. Landscape fabric for a little physical absorption barrier between the liner/tape and soil/food/garden tools. On 1 – part of me thinks I should let that open to allow air to circulate. On 2 – the landscape fabric has an oily sheen to it that looks like toxic gick - have most permies abandoned this stuff? Both additions are easily reversible, so any thoughts on these two would be welcome.
OP Mike Arr, some information on other's use of dimpled membranes for garden beds. I'm a first time poster but long time listener; there was a lack of response to your query, so I registered
Short response: lots of people do this, but not in the North Americas. You had a great idea for lengthening the life of the wood, assuming a few other factors
Fall of 2016 I spent a month in Julbach, Austria helping a friend convert their historic family bakery into an owner apartment and 4 room tourist B&B. This is a place where the hills are alive with music - get out of the way because large farm tractors are pedal to the metal on main street doing 30 mph past the 2 banks in the village. The economy revolves around farming and medical care for the elderly (the town is dying, all the younger folks are leaving). While doing the building renovation, I got to know many of the local farmers and traditional tradesmen in construction. There's a ton of old Europe permie stories from that trip, such as hand chiseled granite blocks instead of brick for walls, but I'll get to the HDPE liner now.
Everyone - and I mean everyone - in the village had lined their raised bed gardens with dimpled membrane. It was the first time, and only time, I've ever seen dimpled membrane lining raised beds outside your photos and my beds since being there in fall 2016. I walked every street in the town, then I asked about it - because I was about to build some raised beds at my place in the US.
This farming community - inundated with snow for months - swears by it. They said it doubles to triples the life of the wood when properly done. They had much advice on how to do a garden bed as well. I'll summarize below:
Dig a foot below grade and put a rock foundation in for the wood of the garden bed. Smooth with concrete (note, they said rock because of the frost line there. I asked about only cement and the response was why 4 ft of cement? Rock weathers well. If you pour cement, dig as deep as you need to go for your climate)
Layer galvanized hardware cloth into the foundation itself to keep out rodents. I poured my cement over the cloth itself.
Put ties, plates, and braces in the cement to elevate the wooden walls of your garden bed above the foundation. Just 1/8 will do. The goal here is to create airflow and zero ground contact. Moisture and soil is the enemy.
Install best rot resistant wood available for your budget. It will rot, eventually. Its wood. The goal is to reduce the long term labor, right?
Install dimpled membrane down to the hardware cloth (1 ft below grade) and 1 inch below the top of the wood.
Do not tape off the top of the membrane. The membrane is there to evacuate moisture and create a barrier for drainage. Air flow is key. If you care about it looking ugly, put a board on top of the bed rail to hide the membrane. Its additional protection for the structure, looks nice, and you can sit on it while gardening.
Anywayshow, these steps create a raised bed wooden garden wherein the wood is never ever ever in contact with soil and minimal water aside from surface rain or snow. UV damage will probably be your worst worry.
Putting this together is work, but this is Permies
(Alternatives: brick beds, poured concrete beds, and general hardscaping alternatives.)
I'd love to give an experience report, but that requires wood to rot in a scenario I've designed to prevent any rotting. I'll update this post in 3-7 years? That said, the octogenarian farmers are fans, and they have more years on me.
Matthew, that is awesome to hear. Thanks for sharing.
My beds are working out pretty well. Tomatoes went bonkers this year and took over most of it. As you can see in my earlier pictures, I did tape the top of the membrane. I planned to screw down a 2x3" on top of the boards to hide the membrane/tape, but I didn't get to it. Now that soil has settled a couple of inches, I'll cut the tape and take a look behind the membrane. I may either remove the tape entirely or add holes to aid ventilation as you suggest, and then screw down the 2x3" in the fall. I will endeavor to provide a progress report on my bed's rottenness every couple of years.
One thing I subsequently learned was that while all raw HDPE is food grade, there can be additional chemicals used in the manufacturing process like pigments and additives that help to release the plastics from the molds (I think they are called releasing agents?) and these may not always be food grade. You have to use food grade pigments and releasing agents to be certified food grade HDPE. It might be worth a call to the company if somebody wants to use a membrane like this since it is manufactured for floors and not food.
I for one would be interested in hearing about any old country Austrian permie techniques that you may have witnessed. I think others around here would as well, especially given you proximity to Sepp Holzer.
I love your use of this material, it allows for air flow between liner and exterior wood so that is simply great. I noticed you added a second soil liner, also a good choice with the dimple liner already in place.
You have reduced greatly the possibility of leachate contamination to your plant roots, good job of thinking things through.
Termites are usually what attacks the wood here in centralTexas. Definitely do not double up boards in termite country. I pulled apart 2 and found termites in between!
I used polyethylene sheet and pine wood for some quick raised beds. But I dug into the ground then put wood on ground level. The poly is crumbled against the sides and the boards are only 6" high, so not a lot of soil pressure will mash the poly against the wood, (which would hold water next to the wood).
In Texas, I don't allow for drainage in my poly lined beds. It's too dry here! The poly lined beds are the most lush veggie beds out of all the beds!
I’ve just lined my raised beds in HDPE dimple membrane but an wondering if to put butyl tape at the top to stop soil dropping down - or will this impede airflow? Any help would be appreciated, many thanks.
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