Raised Bed Advice

[cuffbertt]

Made a start on some raised beds today. Was given some wood from my parents who have just ripped their decking up. So far I've made one out of two beds, and will hopefully make the second after work tomorrow.

Here is a photo of the one that I have completed so far. It's made three planks high of thick wooden decking, and measures 1.8m long, 1.2m wide, and 36cm high (although I'm only filling it 2/3 up).



One question I have, is should I line the inner walls of the bed with plastic liners such as black bags stapled to the insides? The ground will not have the plastic, and will have black membrane stuff that lets water through but not weeds. I'm worried that the wooden sides will rot from the inside after a year or two of having wet soil against it?

So, should I leave the inner walls of the beds as they are, or staple black plastic sheeting to the inside to protect the wood?

Advice appreciated!

[burnie]

I've found that the wood will rot whether you line them or not, you might slow it down a bit, but that's all. Be aware if you put membrane under the bed, you'll have carrots and parsnips hitting the bottom and turning through 90 degrees, they still taste great, just makes me smile.

[bario1]

I lined mine like that, but more to keep the soil from drying out than to protect the wood. Seems to work.

[cuffbertt]

Thanks all, sounds like I have nothing to lose (apart from some black bags!) so I may as well try lining them then.

I've found that the wood will rot whether you line them or not, you might slow it down a bit, but that's all. Be aware if you put membrane under the bed, you'll have carrots and parsnips hitting the bottom and turning through 90 degrees, they still taste great, just makes me smile.

Ahh ok, maybe I'll leave the membrane out then. I thought it was needed to stop weeds and stuff from the grass from coming up through? If I can get carrots that are 9 inches long and touch the membrane then I'll be over the moon

I'm planning on filling it 65% full with compost, 10% with new top soil, and 25% with regular soil out of the garden. Do I need to mix anything like manure with it now or is that mainly to replenish nutrients in used compost/soil after it's been used?

[bario1]

Adding manure (well rotted) won't hurt, but isn't essential either.

[cuffbertt]

Ok cheers, I won't bother this time then. Having one less variable will help me figure out what wen't wrong when it inevitably does haha

[nickdub]

If you are planning on building the raised beds on an area where there is grass/weeds already I'd advise first lifting the top layer as turfs first and stacking that to one side. Then build your beds on the soil which is left after the turf removal - it wouldn't hurt to break this soil layer up a bit by forking it over.

The turf heap you make should be stacked with the grass side down - you can put a tarpaulin or plastic sheet down first if you want, for easier handling. It will take 6 to 9 months for most of this heap to break down and it can then be put back on your raised beds. (Most of the easily accessible goodness in soil is in the top few inches when you are dealing with growing vegetables.)

[ESBkevin]

Or place a layer of brown cardboard down on the ground inside the raised bed. It will ensure the grass and weeds die first and then when it breaks down it feeds your plants whilst not being a barrier to root crops. The decking boards would have been pressure treated when new and have a reasonable resiliance to rot (depending on thier age already).

[Kirk]

Most weeds will get killed off by being buried under the soil. Never found that a membrane underneath was much help, if you dig deep then you end up digging into it and then you have real fun as half of it is half way up the soil in the bed.

And at some time you will likely decide to add manure or whatever and dig it in deep.

[snohare]

A membrane won't stop the wood from rotting, but it will slow down moisture loss via evaporation, and give a different temperature and humidity gradient for the soil inside. (Are you expecting any heatwaves/high average wind speeds ?)
One good reason some people put down the woven polyethylene mulch sheeting (you know, the shiny stuff that turns into ragged streamers at the edge if you don't cut it using a blowtorch) as a base, is to prevent voles from popping up from underneath and nicking all your root vegetables. Worth thinking about if you are planning on growing potatoes, and you are surrounded by grassland.
(Personally I put down a double layer of chicken wire in the past, but I don't know if it worked - I never saw any voles !)

[burnie]

I put membrane under my beds as I don't walk on them, so I am no dig gardening now. You get wind blown seeds, but I've had no couch grass or any other nasty's that live in my garden.

[TheCyclingProgrammer]

I chose to line my raised beds using a good quality weed membrane. They are 14 inches deep and filled with a good quality, weed free sandy topsoil and compost mix, so I didn’t see any need to expose the beds to any potential perennial weeds lurking below (especially as the ground my beds placed on was previously covered in dense weeds including bindweed as it was used as a rubbish pile).

This will slow down rot, it won’t stop it completely. My beds are pressure treated (but safe for growing) and I expect them to last about 10 to 12 years.

[Mark_Riga]

I've found that wood seems to rot most where it is in contact with vegetation, particularly if it is lush (eg fence posts with tufty grass at the bottom) - it probably harbours damp longer than soil on its own would. So if it was me, I would cut out a strip of the grass on the outside of your new bed wide enough for a hoe. I'm thinking about making a couple of raised beds and will have a woodchip covered path over a membrane between them to prevent vegetation on the outside (not a lot you can do about vegetation on the inside).
Also, once a year, you could inspect them for rotting and, if they are screwed together, you could may be switch the lower planks and the top ones if the bottom ones are showing any sign of rot.