Way to Treat Gardening Bed Wood so it Lasts Longer?

[sheeshshe]

I want to make some raised beds for in front of my house, to plant flowers in. I would like them to last a long time. I could buy pressure treated, but my neighbor has a pile of wood he made with his saw mill that he would like to give me. Is there a way to treat it so it lasts longer?

[rainbowgardener]

I don't think you can do home pressure treating. But I seal the wood for my raised beds with varnish stain. You can even use marine spar varnish which is what they use on boats.

[imafan26]

Wood does not last a long time. but the right wood and under good conditions can last 10-20 years. Cedar and redwood will last longer than pine.

[rainbowgardener]

Dimensional lumber (eg landscape timbers, 4x4s ) lasts WAY longer than flat boards.

The first raised beds I ever built were of boards. I used corner braces, middle braces and everything I could think of. Still in 3-4 years they were all warped and falling apart.

At the next house, I built raised beds out of stacked 4x4 pine fence posts (alternate stacked at the corners) held together with steel rebar pounded down through the stack. I sealed them with varnish. :



At the time I moved away from that house, they had been there for about 14 years and were still going strong. I did recoat the outside every few years, mainly for cosmetics, but of course once the dirt is in, it's never going to get redone inside.

This is my most recent creations. It's landscape timbers. Not nearly as good wood as the pine fence posts, but cheaper. These only cost me about $30 each to build, which I think is about as cheap as you can get for an 8x4 raised bed. Probably won't last as long as the 4x4's.

[sheeshshe]

wow, I have a lot to think about. my neighbor has the regular pine boards he made. is it even worth it if I put the sealer stuff on it? or should I just invest in the thicker stuff right off the bat?

[rainbowgardener]

Well, free is always good. The varnish stain isn't all that expensive. So you could take him up on it, if you understand that you are likely to get three to five years of use out of the beds (if you do a good job with sealing it, using corner braces, etc) and then they will have to be redone.

[Farmerboy]

Ace hardware stores sell wood preservative that can be brushed onto wood to make it water resistant and rot / mildew resistant. But the preservative is so expensive that you would be better off just buying pressure treated lumber.

[imafan26]

Be careful with wood preservatives, depending on what you are using, it may not be good for growing vegetables.
https://extension.missouri.edu/p/G6985

My raised bed is made from dry laid hollow tile. It is easy to build as long as you get the first layer level, and it is durable, It does not rot. Since it is dry laid, the water will weep between the tiles. I have my bed for over 25 years. Leaching is not a problem, but I have an acidic soil to start with.

[ElizabethB]

My very first raised bed was made with cinder blocks. When I built my boxes I failed to consider the leaching of lime from the blocks. After the first season I removed all of the blocks and wrapped the inside and bottom with heavy duty, construction grade, garbage bags. That did the trick. The boxes were for vegetables. I planted annuals in the holes.

I thought I was so artsy - I panted the outside of the blocks. Some had geometric patters, others free form finger-paint. I even painted simple flowers, butterflies and birds on some of them. It was disgustingly cute.

Keep in mind - I was MUCH younger and had a lot more energy than I do now.

[Vanisle_BC]

I have old raised beds 16-24" high. (I can sit on the edge of them.) The sides are rough 2x red cedar boards on rough 2x4 cedar frames. They've lasted a good number of years but they're deteriorating; one in particular is falling apart.

After looking at rainbow's photos of her handsome raised beds of stacked 4x4s (don't know how to reference her post) I priced "rough" (4-1/8") 4x4s locally; about $15 Canadian for an 8 foot piece. I have 16ft beds. If I went 4 timbers high (16") that would be $60 per 8 feet of wall - or about $300 for a 16x3.5ft bed, not including rebar etc: too much for our budget. Dressed (3-1/2") boards are just a couple of dollars cheaper. Next best would be landscape ties (untreated) at about half the price of the rough 4x4s. They're only (I think) about 3-1/2 inches high so maybe I would use a stack of 5. Might do that. It wouldn't be as long-lasting (or pretty) as rainbow's 4x4s but probably a lot better than what I have now. This may be the way I should go.

At first I though I would need pretty long rebar for anchorages down through all that wood and well into the ground (plus a lot of drilling) but on second thoughts only the bottom strake has to be anchored. The rest could be simply spiked on top of each other, maybe each (9 inch?) spike going through 2-1/2 strakes. Probably still have to drill for them, individually in each piece, with potential for line-up mismatches down through the stack. I only have light-ish power tools, and no long drill bits.

Comments welcome.

[ID jit]

If you want rot free wood, look into oil stabilizing wood. It isn't really practical for raised beds though. "Butcher Block" oil would work, but it is a lot of time, effort and money.

Another option would be getting a cheap hvlp spray gun ($20 or so) and spraying the cut-to-size board with food grade fiberglass resin thinned with denatured alcohol. Dry pine will really suck the stuff up. Apply light coats and allow the resin (or 2 part epoxy) to set up and cure before applying the next light coat. Keep applying light coats followed bu cure time and a scuff up sanding until you get the resin to "flash" (look shiny and liquid-like). When that happens go heavier with the coat to just before you get runs. Result is pretty much food-grade-polymer encapsulated wood.

Probably not practical for most people though, unless you have a fair sized compressor and don't mind learning how to deal with spraying 2-part stuff.

You can brush, 2-part epoxies, resins, urethanes and the like If you thin them down with denatured alcohol, use a slow set hardener and usually a nylon or natural hair brush - just mix smaller batches and overlap new batch onto the last batch before it sets up. Almost all polymers cure to inert if mixed correctly.

Mid summer I built a small box out of 3/4 pine I had laying around and hit it with 4 coats of glass resin inside and out. It has been holding water for maybe 2 months now with no issues other than algae build up and skeeter babies. (This is a test run for maybe building some raised 4' x 8' SIPs)

[Vanisle_BC]

Thanks, ID jit.

Actually I've been pretty familiar with fibreglass and resins both polyester and epoxy, though not with spraying any of them. But nowadays I try to go as "natural" as I can, especially with foodstuffs. And those materials are not cheap for use on large areas.

[imafan26]

I use hollow tile for my beds. Too many termites and wood rot in a wet humid climate. Redwood and cedar will last the longest but 15-20 years if you don't have them sitting in water.

[MoonShadows]

You folks don't worry about putting stains, preservatives and oils on your raised garden beds?

Besides cedar and redwood, a great, long-lasting wood to use is Tamarack (a.k.a. Larch). We have a local saw mill that we buy Tamarac from in 2" x 10" wide x 10' lengths. Tamarack grows most commonly in moist areas such as swamps, bogs, streams, and the edges of lakes, and lasts for years without any treatment whatsoever. It is also much cheaper than cedar or redwood.