Raised planters / bed - longterm effects of soil on wood

[rafezetter]

Edit: seems somehow my google-fu completely failed me and I managed to miss raised bed information regarding wood and liners etc in my search but I've found some now.

As per the name - I'm in the process of planning a large (1.6m x 8m) raised bed and I'm utterly clueless on the longterm effects of soil on wood for this usage. I'm trying to make it from mostly reclaimed wood that we have a lot of, so it's not pressure treated.

Would painting it with waterbased wood preservative on the soil contact side have any real longterm benefit?

It's quite probable that I may still be living here in 10 years, so it needs to last at least that, but as long as possible ideally because it would be a major understaking to re-do it for the next people when it rots. 6-8 dumpy bags of soil.

The design is a double skin - using pressure treated 6 x 8 sleepers we have as the uprights sitting on patio slabs - which will be under the line of decking so won't be seen and will be treated with bitumen paint, with 2x4's notched on the back side then clad with old reclaimed larch feather edge (which is 2x thicker than the stuff you can buy now) on the outer face of the 2x4 and.....???? on the inner face.

I've considered teram (soil liner) as a "bag" instead of lining the inner with wood, but that might get damaged if someone takes a fork to it - I don't want to to go the expense of a poly liner on top of wood, so if I just line it with bare (not pressure treated) wood what sort of lifespan can I hope for?

bitumen paint will prolly affect the soil - thompsons water seal - shou sugi ban and smothered with cheap teak oil....?

edit 2 - interesting a mixture of beeswax and mineral oil, really soaked in, or raw linseed oil are good alternatives to extend the life of the wood.

 

[AndyT]

It does start to sound like some blocks or bricks would be a better bet. Aren't timber raised beds an idea made fashionable by TV makeover shows in need of something new, rather than an established, practical solution to a problem?

 

[rafezetter]

I would agree longterm a brick or block system would be better, but I don't have a lor of those lying around compared to all this timber.

 

[Sheffield Tony]

I guess they became popular on those makeover shows because they were often working on a newish garden left by builders with a thin skin of topsoil over rubble etc. But they have become far too popular. There are AFAIK 3 good reasons for raised beds - terrible soil that can't be improved, waterlogged ground, and to allow for the physical limitations of the gardener. I suppose you also need to add to that "because I like the look".

It sounds here like this is a fairly substantial affair - I would guess the wood would hold up in soil contact for 10 years or so ? **** of a job when it starts to fall apart though.

 

[Alder]

I have stapled used compost bags to the inside of my raised beds. Hopefully it extends their life and gets rid of the bags.
Russell

 

[rafezetter]

I guess they became popular on those makeover shows because they were often working on a newish garden left by builders with a thin skin of topsoil over rubble etc. But they have become far too popular. There are AFAIK 3 good reasons for raised beds - terrible soil that can't be improved, waterlogged ground, and to allow for the physical limitations of the gardener. I suppose you also need to add to that "because I like the look".

It sounds here like this is a fairly substantial affair - I would guess the wood would hold up in soil contact for 10 years or so ? **** of a job when it starts to fall apart though.

yeah that's the bit that concerns me.

I'm building it to deal with the area of the decking that's always in shade and has rotted faster than the rest, and because there's no other greenery at the house at all. I made some movable planters which have been nice but now I have permission from the landlords to do this, I'd like to mitigate that issue you mention above as much and for as long as I can without it costing hundreds.

Alder - good idea and so obvious, plastic bags #-o - the UV issue.... isn't, below the soil line.

 

[AJB Temple]

My wife made me make some raised beds in our kitchen garden, which is about the size of an allotment.

I knew this would only be a temporary set up as she was bound to re-plan eventually. I used treated gravel boards and spiked fence posts. Three years on she has just ripped them all out. The gravel boards have not rotted though some of the posts have. The paths all had that black commercial anti weed membrane laid first. The paths were done with wood chips (free source) which worked well.

In our case she wanted to create paths through the beds, improve the soil (the area had been used for a lot of bonfires) and get decent drainage as we are on clay.

When she ripped the beds out, she was intent on having an array of smaller, thicker and taller raised beds, similar to Adam Frost's set up on Gardeners World and the similar arrangement used by Monty Don for some veg growing. She changed her mind and has gone with a no dig and soil mounds system directly in the ground now for this year.

My observations: if you use raised beds, then you will need to fill them. High quality growing medium is expensive. We had a fallow year and a truck load of manure and wood chips, which was near free (tons of it) but involved a lot of barrowing. Even so, we had to buy bulk compost to create useful beds. That was not cheap. You must factor this aspect in as the soil is more important than the surround!

We made our beds too big and not high enough. I think there is pretty much no point doing it unless the soil level is raised by at least a foot and preferably more. And you need to be able to reach the centre of the bed from both sides.

A big advantage is that raised beds define and contain paths well. But - this also consumes space, especially when you need to take account of wheelbarrowing around the corners.

I put a water supply in at the same time. That is essential as raised beds need more watering in our experience.

If I were to do it again, I would make the beds either from low grade oak sleepers, or from thick scaffold board seconds. I would make them fairly small and at least 18" high. I would be looking for 20 years life minimum. Using untreated softwood timber will result in bottom rot by year two and I would not waste labour on that.

 

[rafezetter]

My wife made me make some raised beds in our kitchen garden, which is about the size of an allotment.

I knew this would only be a temporary set up as she was bound to re-plan eventually. I used treated gravel boards and spiked fence posts. Three years on she has just ripped them all out. The gravel boards have not rotted though some of the posts have. The paths all had that black commercial anti weed membrane laid first. The paths were done with wood chips (free source) which worked well.

In our case she wanted to create paths through the beds, improve the soil (the area had been used for a lot of bonfires) and get decent drainage as we are on clay.

When she ripped the beds out, she was intent on having an array of smaller, thicker and taller raised beds, similar to Adam Frost's set up on Gardeners World and the similar arrangement used by Monty Don for some veg growing. She changed her mind and has gone with a no dig and soil mounds system directly in the ground now for this year.

My observations: if you use raised beds, then you will need to fill them. High quality growing medium is expensive. We had a fallow year and a truck load of manure and wood chips, which was near free (tons of it) but involved a lot of barrowing. Even so, we had to buy bulk compost to create useful beds. That was not cheap. You must factor this aspect in as the soil is more important than the surround!

We made our beds too big and not high enough. I think there is pretty much no point doing it unless the soil level is raised by at least a foot and preferably more. And you need to be able to reach the centre of the bed from both sides.

A big advantage is that raised beds define and contain paths well. But - this also consumes space, especially when you need to take account of wheelbarrowing around the corners.

I put a water supply in at the same time. That is essential as raised beds need more watering in our experience.

If I were to do it again, I would make the beds either from low grade oak sleepers, or from thick scaffold board seconds. I would make them fairly small and at least 18" high. I would be looking for 20 years life minimum. Using untreated softwood timber will result in bottom rot by year two and I would not waste labour on that.

hmmm interesting - the soil was going to be free (hoped anyway) as I see lots of facebook marketplace posts of free soil and I'm not expecting to be able to use it right away - we have about 10 or so large bags of compost to mix in with that (and I'll be adding sand for better drainage) and the planters I have are all pretty rich as they've been doubling as composters since I've not planted or seeded them for a couple of years but still produce tomatoes and potatoes, spring onions and some lovely poppy flowers of a variety I don't recognise.

The soil height all in will be around 2.5 feet deep, thereabouts.

I have wondered about the 1600 width front to back as probably too wide, but that's being dictated by something else at the front edge and making it narrower and having decking behind it against the wall is just so much trouble and will suffer the same problem, always in shade and rotting, so going to the fence (which handily is 50% block wall 5 foot high at the bottom) is the only real option.

I understand all of this is a "make -do" scenario, but I'm not going to throw money at this I don't have to spare and trying to rectify a situation with a large section of dangerously rotted decking the landlords aren't that keen to pay to replace.

Going back to the soil, I'm not looking to grow prize winning leeks or similar as I'm not actually that much for growing, but I do like to see stuff growing - although part of it will be separated (possibly) so I can have a Japanese Acer (ideally) next to the covered seating area and I understand I'll have to tinker with the soil chemistry there.

 

[Doug71]

I put in 12 raised beds about 8 years ago, used up loads of 3" timber I had kicking around, was a mix of redwood and whitewood. Gave them plenty of preserver and lined them with visqueen.

Some are fine, some look tatty and some are falling apart.

 

[AJB Temple]

Acer Palmatum will grow happily in pots. I have been building a Japanese style garden in the past three years and we have I guess around 30 Acers of various sizes. The growers who supply for Japanese garden designers will field grow and ball the roots, or grow in pots, even up to quite large trees. They do take off when they are in the ground though.

I would be super wary of "soil" that people give away free. You have no idea what is in it (couch grass and other invasive weeds, along with rubble and rubbish very often. No one gives away high quality loam topsoil.

If you have poppies coming up, then chances are these will have lain dormant for years and are activated when the soil is disturbed. When I dug my ponds out (with an excavator) I put the clay and topsoil into large banks about 2 metres high (they settled after that) and in the first year a lot of poppies appeared. Quite amazing.

Good luck with your project. As it is evidently a rental I wouldn't spend much h either.

 

[AndyT]

My response may have come over as a bit curt. I guess I was projecting my own mistakes!
I could have said, Don't follow Geoff Hamilton but using old floorboards, it will rot out in a few years. And if you replace them with scaffold boards, even sloshing on as much preservative as you can, they still rot in less than ten years.
I'll get round to some brickwork one day...

In your case, I'd use up whatever rough wood is in the way and not worry too much.

 

[rafezetter]

My response may have come over as a bit curt. I guess I was projecting my own mistakes!
I could have said, Don't follow Geoff Hamilton but using old floorboards, it will rot out in a few years. And if you replace them with scaffold boards, even sloshing on as much preservative as you can, they still rot in less than ten years.
I'll get round to some brickwork one day...

In your case, I'd use up whatever rough wood is in the way and not worry too much.

Don't worry Andy, I certainly didn't take it that way - (and I'm not entirely convinced you're even capable of it having met you a few times).

The linseed oil sounds promising as a second defense after plastic bag liners.

I see your point Doug, but looks like your beds have been wicking water up from the ground whereas mine mostly won't if I get it right.

The soil thing - yeah I get your very valid points, of it potentially (probably) being poor, but I'm not averse to screening, or maybe I can get away with the bottom half being lower quality and then using the compost and rich soil I have along with some pre-screened soil mixed for the upper layer, 16 inches of "good stuff" should be plenty?

Again not going for award winning leeks - but leeks might be on the cards, so maybe I should look for info about what's a reasonable soil composition "all rounder".

Thanks for the replies - it's helped to clarify certain fuzzy edges of my ideas.

 

[Trainee neophyte]

Width of a raised bed is limited by being able to reach the middle from either side. If you can't get access from one side, then very narrow. I made a load of grow-beds that were too wide to reach the centre, so you have to walk on them - poor planning. 4 feet is standard, I believe, do 2 feet if you can't get to both sides. Your gardener's arm length will be the deciding factor.

Have a look at wicking grow-beds; you have the right size to make a great system of self-watering wicking beds. Lots of work, though.

Another option could be to have pots/planters inside the raised bed - the woodwork being cosmetic to hide the support for the planters. It would resolve the soil/wood issue by contains the soil in the planters.

Finally, you say this area gets no sun. Is this ever going to grow anything? Is it worth the effort?

 

[D_W]

As a kid, my parents put in raised beds for a garden as we had rocky soil. They were both children of farmers, so they wanted the raised beds to be serious and made about a dozen that were big enough to put a tiller in - like a big tiller, not a 2 cyle or electric type.

The sides of the raised beds were logs, untreated, and I'm sure we just cut them from the woods because that would've been free. The ends were capped with 8/4 red oak because that's what we had extra of - pine would've been a purchase to make.

The raised beds lasted at least from the time I was 6 to the time that I was 18 and the ends hadn't broken out (they outlasted my parents' desire to garden).

From a toughness standpoint, the logs (guesstimate 8 inch logs, not something huge) debarked themselves and then grayed and didn't do much quickly after that, and they were hard enough that if a tiller tine hit one, they were only scuffed.

As far as treatment methods for wood - if there was something inexpensive to do that cost less than just replacing the wood several years from now, it would probably be made as a commercial product, but raw linseed oil (in the amount that can get soaked into wood), beeswax, etc, may cost a lot. Some of the different oils (even when labeled as raw) may have driers in them that you don't want in your garden soil.

 

[rafezetter]

Width of a raised bed is limited by being able to reach the middle from either side. If you can't get access from one side, then very narrow. I made a load of grow-beds that were too wide to reach the centre, so you have to walk on them - poor planning. 4 feet is standard, I believe, do 2 feet if you can't get to both sides. Your gardener's arm length will be the deciding factor.

Have a look at wicking grow-beds; you have the right size to make a great system of self-watering wicking beds. Lots of work, though.

Another option could be to have pots/planters inside the raised bed - the woodwork being cosmetic to hide the support for the planters. It would resolve the soil/wood issue by contains the soil in the planters.

Finally, you say this area gets no sun. Is this ever going to grow anything? Is it worth the effort?

It does get some sun but not as much as the rest, maybe 1/3 of the day's sunlight in summer and even less in the winter, and that area of decking has rotted much faster. I may well trim the top off the fence and swap it for trellis if our nice neighbors are amenable. Flowers seem to do fine, and as I said seeds from composted tomatoes and pototoes and other stuff has popped up, so stuff will grow.

 

[Inspector]

I made beds of untreated fir 2x12 before and they lasted 10 or more years. I stapled some clear plastic to the insides to help keep them from rotting. Don't know if it helped any.

Just finished making 6 beds 2 feet high, 3 1/2 feet wide and 8 feet long out of pressure treated 5/8" plywood and pressure treated 2x4, framed like a wall with the 2x4 on the outside. I lined them with the dimpled plastic used to shed water from foundations. I don't know if the dimpled plastic will improve the ability of the plywood to dry out or not but it seemed like a good way to keep the treatment away from the veggies. Have enough to line a couple more beds if the boss decides I need to make more. :roll:

The best beds I have ever seen were made by one of the woodworkers in our club. 6x6 beam framed tables with the beds, about a foot or more deep, on top. The top of the beds are at waist level and it makes it easy for the two of them to work. They are in their mid 70's so perfect.

Pete