I did a search but couldn't find this discussed anywhere in precise details:
How long do scaffolding boards last used as raised beds?
We are thinking of building raised beds this year. We have had mixed success with conventional vegetable beds in the last 10 years, but after seeing the garden being completely waterlogged during last summer and even more so during this winter (so great to see the sun in these last few days!) we have made up our minds that we need some raised beds to hopefully get some better drainage in the beds.
We were thinking of using scaffolding boards (about €5 per 8ft length here in West Kerry, Ireland) but was advised by a guy making polytunnels to use pressure treated 9x2s (€20 per 16ft lengths). This being double the price, but also double the thickness and treated so should last at least twice as long. Looking from that perspective they work out at more or less the same price/year.
Anyway: an obvious downside of treated wood is the possibility of chemicals leaching into the soil and ending up in our food. One of the reasons of growing (some of) our own food is to avoid the food being chemically treated, so this is obviously an issue..
Also spending twice the amount of money at once is a thing to be considered as well.
So to make a long story short(er) and because there are tons of people using untreated scaffolding boards for their raised beds I was hoping somebody would have used them long enough to know when they start to rot in our lovely damp Irish conditions.
I have 4 year old scaffold boards that are starting to get a bit fragile at the corners (I'm in the East Midlands, so not quite as damp as your area). And I have beds made from pressure-treated decking boards- at the same age these remain somewhat sturdier. I didn't paint these or anything, just stuck them in the garden.
I purchased the decking as wonky boards that had gotten wet and were no longer any use for actual decking, so they were incredibly cheap- keep an eye out for any bits of free wood that would do the job, then you don't feel so bad when they disintegrate!
Edwin de Groot
posted 3 years ago
Thanks for your reply. Did you treat the scaffolding boards with anything?
I don't know much about scaffolding boards, but -NEVER- use pressure treated ANYTHING, anywhere near anything your going to eat/drink, yes, because of the chemicals.
Don't do it.
Most timber cut(kilned) wood in raised bed walls tends to last anywhere between 3-15 years, depending on weather, the wood itself(pine/spruce) and water, etc, and if you line the beds with a liner.
A 5iver at 8ft, something that's going to last 5 years plus, that's a fair good deal, depending on how many beds your going to be putting in, anyways. But a quick google search tells me that most of those scaffolding boards are chemically treated too, they're made with construction in mind, and most of them seem to have at least some kind of fire retardant on them.
But an 4x8' bed would could cost you 15 per bed, plus hardware to hold it together. Is there anything commercially available that would cost the same for less the work, for the number of beds your making?
What works even better and often free? Bricks, old used bricks that you could probably salvage for, for free in most places.
Take a look around you, if there's construction going on, you should be able to salvage something off those sites, or find inspiration from other things.
You can use paving stones on their ends, buried to make a bed, but you might need stabilizer posts.
You can use cord wood lengths, post driven like into the ground.
Some people make a box-bed out of a metal sheeting like corrugated roof sheeting.
And some people take a length of corrugated culvert, cut it into shorter lengths to make round garden beds, or cut it length wise to make troughs.
A raised bed is basically a tiny fence, it just has to be sturdier to keep the soil in, especially if your doing bigger beds (and if it's to wet and rainy, not recommended, or you end up with mud-pools).
A friend of mine with virtually dead soil(clay, nothing but) has to resort to using cheap kiddie pools, and edges them around with stone or bamboo edging when he can get it cheaply enough.
Another one has links to the fishing industry, and uses old fish/icy trays. You can usually get them cheap from fisheries because they have defects like cracks or broken handles from use, if not free, good enough for holding dirt in, and look, drainage. My family in the past has grown a fair amount of carrots and onions and beets to great success out of them(until the neighbour pesticide sprayed his yard next door and it wafted over the fence). That being said, plastic totes work for this if you have to, and you just tip the bin over and break apart the soil to get your bounty, then dump your soil into the compost pile to overwinter, to replenish the soil. This all, of course, depends on how much your trying to produce. We grew less than a half dozen trays to get just enough 'special' vegetables for bottling.
I've tried all sorts of materials for raised beds -- wood, tyres, stone, brick, clay roof tiles... Brick is what I have found works best. The bricks we use are a very long flat kind that's normally used for thin partition walls. Possible old roofing slates / tiles would be a local equivalent in Ireland. They can either be stuck in the ground or held in place with rebar. Should outlast any kind of wood.
"If you have built castles in the air, your work need not be lost; that is where they should be. Now put the foundations under them.” - Thoreau
I didn't treat my scaffold boards with anything. I do have some painted scaffold boards (just painted with water based fence care paint) but they're only a year old so I can't judge how long they'll last!
I've found that bricks and blocks harbour even more slugs than the wood- but I just stacked mine up without mortar, so lots of places for the slugs to hide! Upstanding paving slabs might be a good one to try.
Edwin de Groot
posted 3 years ago
Thank you for your great replies, really helpful!
We had a change of plan..
We are thinking after reading all the bad prognoses here and on other forums ("it will rot" is the general consensus) of using standard concrete building blocks for our raised beds. The price for those is roughly the same (per length) as scaffolding board would be, but it will last forever!
Only worry is drainage as we wouldn't want to be building a swimming pool. But I suppose with plenty of drainage holes between the blocks and the soil being higher than the surrounding area water should drain away.. (hopefully)
You may not need scaffolding timber at all. I am in the process of building a raised bed garden for the same reasons as you. Flat, poorly drained area of halfway decent soil.
Process is to use a digging spade to turn the topsoil layer over upon the adjacent spot. That leaves a hole in the ground. Then use a digging fork to loosen that layer. Upon that loosened layer put down a layer of heavy mulch of some type. I'm using hay......about 6 inches, or about back to flush with the adjacent soil. Then move over the width of the spade and turn that layer over onto the hay. (It will now be higher than the adjacent soil by about as much as you would have had by building your raised beds, and bringing in soil to fill them.) Keep going until you finish your row. If I were you, I'd make these mounds about 1 yard (meter?) wide for as long as you want to make them. If you want to go wider, go wider, but not much more than you can reach into from your pathway. The edges may slough off a little, but not as much as you would think and a bit of crown on them is not bad as they allow excess rain to slide off to the side.
To make the second row, leave a walkway or pathway between your mounds. Maybe 1.5 to 2 feet? Then repeat your second and additional rows and keep going until your garden is as big as you want it to be. Then.......go back and turn the soil left in the pathways over on top of the finished mounds. That will leave a very high mound, with a moat between them. By now you have a raised bed that is maybe 18 inches or so in profile from the top of the mound to the bottom of the moat. You will have almost a foot or more of dry soil for your root zone, with ample moisture below. The layer of topsoil is twice as deep as it was, with a well drained root zone below.
So now, if you were to look at this in profile, your mounds and moats would look like the edge of a sheet of corrugated roofing. Deep down under the mounds you have a layer of disturbed, loosened soil with a layer of hay or mulch on it to start working down.......covered by nearly a foot or so of loose soil elevated well above the adjacent soil, and between each of these mounds is an open moat for excess water to drain into. Fill the moats with hay or mulch to keep the weeds down and as something to walk on so your feet don't get muddy. As the mulch rots down, flip it over onto your raised mound for organic matter, then refill the moats with mulch.
In a way, these raised beds are little mini hugelkultur mounds.
Edwin de Groot
posted 3 years ago
Thanks for your reply.
The way you described is more or less how we have been doing it for the past 10 years (minus the straw). But because our garden gets completely waterlogged during a bad (Irish) winter and sometimes even during a bad (typically Irish) summer we needed something to raise the level of the beds even more than we can in the way you are describing. 18 inches won't stay up without support with our soil and the amount of rain we are getting..
posted 3 years ago
Is it dead flat or do you have enough relief (slope) that you could install underground drain tile?
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