Raised Beds, Wood or Plastic?

[Garden Manager]

I grow my veg in raised beds (only 6"high). I originally made them 17 years ago from wooden gravel boards, however they are now rotting away and falling apart. Instead of wood replacement I found a kit system of interlocking recycled plastic boards, which not only are virtually no maintainance and rot free are also easier to build. I have been replacing them one a year for the last couple of years. Another replacement is planned this winter.

One thing I have noticed with the plastic beds is that they do seem to retain moisture more than the wooden one, which is fine for crops that need moisture and in dry weather, but could be a problem for crops that need good drainage or in very wet spells. Fortunately my soil isn't that heavy (chalky loam), otherwise I could have a problem and need to think again about renovating my beds.

I was wondering if anybody else had plastic raised beds and and if you have noticed any differences groing in them compared to other materials/ methods?

Any input appreciated.

[Garden Manager]

[squeezyjohn]

Wood certainly does rot when in contact with soil after a certain amount of years!  It needs to be treated in order to last long enough to make it worthwhile (and be quite thick) - but then there's the concern that the treatment can leach in to the soil and be less than beneficial.

I've never seen any plastic item which doesn't photo-degrade over several years of being in the garden - I imagine that they aren't designed to last for more than a few years.

My raised beds don't have any edging - they're more like 4.5 foot wide speed bumps ... but they are getting annoying as all the soil/manure eventually ends up washing down on the paths.  If I get around to making any sides for the beds I will be using bricks or breezeblocks as I think that will actually be a more permanent solution.

Regarding the moisture ... I would put plants which love the moisture nearer the edges and grow the stuff that needs to be free draining towards the middle of the beds where drainage is likely to be the same as in open ground.

[picman]

Timber attracts pests . 12 " x 6'  Concrete gravel boards , sealed on the inside work very well but a little costly, but last a lifetime   

[Vinlander]

This is a key question.

I agree with Squeezyjohn about sunlight and plastic - and the effect is 10x worse if you are expecting structural strength from it - like holding back tons of soil. Basically it becomes brittle even before it loses all its strength and actually falls apart.

Plastic ground cover sheets/tarps can be protected by layers of woodchip or paper, but the only plastics that you can rely on in sunlight are UPVC and polycarbonate.

These are premium grades and very unlikely to turn up in horticultural pre-packs - despite the fact you are paying more than it would cost to buy brand new black UPVC - for example a 2x1m surround 150mm high in unnamed "recycled plastic" will cost £30-40 while the same 6m x 150mm of black UPVC fascia  would only cost £25 (plus a bit of work for a lifetime's use).

I like to use reclaimed 8 inch joists where I can - they last decades despite being untreated (because they date from the 30s - I rescue them from skips - putting usable wood in skips is a sin). I also like to use UPVC sections cut from reclaimed door frames (100x70mm) below the soil surface to prevent the soil escaping under the wood, especially as my paths are deep woodchip and the UPVC at path level gives me another month's grace before I have to re-fill them.

However even supported slightly above the path they still gradually rot, and the damp soil side rots outwards twice as fast as the other sides that have a chance to dry.

I'd like them to last even longer. I am experimenting with lining the inside with plastic sheet to keep the damp soil off them (no problems with sunlight of course), and it seems to work - the hidden surface of the board has some chance of drying out in summer, and there are less cavities of rot for the slugs to hide in (which makes them more visible so seem more numerous but I'm pretty sure they aren't). However it's still pretty damp - I'm about to try putting a layer of vertical sacrificial sticks spaced every cm or so between the plastic and the good wood to allow some air circulation - I'm just concerned that the air columns really will encourage slugs...

Cheers.

[daveyboi]

I used treated timber boards for my strawberry bed



The planks were 19mm x 100mm x 2.4metres from Wickes with metal angle corners and center supports driven into the ground.

The inside of the boards and bottom edges have been painted with two good coats of black bituminous paint
The other surfaces were left uncoated so the timber can dry out in the summer to help it stop rotting.

This seems to work as this bed was made in Autumn 2008 and there is no sign of rotting at all yet.

[Tee Gee]

I prefer not to use any form of edging unless it is absolute essential.

What I like to do is excavate my beds and this fluffs it up a bit above the original level

Then I fill the paths which are slightly lower than the new soil level, up to soil level with wood chipping which the council give us FOC.

I find over the year the soil and the chippings slump down again to its original level, so the following season I just use the same process again.

[Vinlander]

Hi TeeGee,

Eventually as you add more and more woodchip the whole plot will rise up every year - this is a good thing - especially if you have heavy soil and even more so if like mine there is a downhill area that flooded until I did something similar (I used to allow the paths to be the level of the edging but they just became canals filled with what you might call quickchip, meaning it came over your boots when you stood on it).

I have accelerated the process by digging the unused topsoil out from under the paths, and now I have beds over 15cm higher than the winter water table - I'm looking forward to when the beds and paths are 30cm above and I can walk on damp woodchip instead of quickchip! Unfortunately I'm not allowed to mess with the paths around the plot so I'll still be sliding around on those.

Cheers.

[Crystalmoon]

Hi I use plastic raised beds & they are very sturdy & easily come apart to be moved around the plot which really helps me with crop rotation & they can be stacked on top of one another to make even higher beds. Some I have had in use for over 10 years with no signs of deterioration, they are made by Garland. They are only a square foot in size but I think you can buy extension kits but I prefer to use the small beds as it suits the way I grow crops. Ants do tend to like living in them as the ridges on the inside of the boards make great ant nurseries but disturbing the soil makes the ants move on so it really isn't an issue. They can be very pricey to buy but I managed to get all 12 of mine in sales at half price or less.

[Paulines7]

We bought 3m scaffolding boards to make our raised beds and also used some left over breeze blocks.  The boards were about £9 each but we bought in bulk. 

We have made a narrow raised bed in front of the chicken wire fence with breeze blocks and this has been useful for growing peas. 

Three (3 x 1 m) raised beds are completed so far, using the scaffolding but we have plans to do more as we clear the area of weeds.  OH has put stakes in to support netting, fleece or wires.

[Garden Manager]

These are what i have been getting and installing. Dont know if its the same as 'Crystalmoon' uses or not.

http://www.linkabord.co.uk/index.php?route=common/home

As well as veg beds i also have one for a row of Autumn Raspberries. Dont know if is just coincuidence but this year that row produced some of the best raspberries i have ever grown! I am thinking the plants benefitted from the deeper, cooler, moister rootrun the beds provided. Planning to do another row this way over the winter.

You may be right about durability. Not expecting these beds to last as long as the old wooden ones, but having said that  they look smart, are easy to assemble and can be moved and reused more easily than wooden beds.

I am just a bit concerned about the moisture levels within the beds as stated in my original question.

[Crystalmoon]

Hi Garden Manager the beds you are using are different to mine but probably similar enough to compare....I do find the beds retain moisture in a good way when my heavy clay soil has become concrete. When the rain is heavy the beds drain well. I am able to grow things closer together in the beds which means I don't really lose the growing space of the paths between them if you get what I mean. I add compost manure etc to the clay when I first fill the beds so the soil is so much better than the clay for direct sowing of seeds. I don't have to do heavy digging anymore which is brilliant for me as I have bad arthritis. I can sit on my gardening stool to tend to the beds which also really helps me physically. All in all I think it is the raised beds that actually enable me to keep up an allotment.