Lining a raised bed?

Following on from my new raised bed query yesterday, I've just read the instructions that came with the kit, and they state "As the material is pressure treated, if using to grow plants for human consumption it is recommended you line the frame with polythene."

I would have thought that this was a bad idea - trapping damp between the polythene and the timber.

Is the pressure-treatment really hazardous?  And if it is, my compost bins are made of pressure treated wood - are they going to contaminate my compost making it unfit for use on the veg patch?

What do other people do?

The polythene will actually help to preserve the timber - it reduces the moisture in contact with it considerably.

We have railway sleeper retaining walls to make a level area for our veggie patch which then is laid out with raised beds made from pressure treated roofing timber. 

We lined the insides of the sleepers to prevent both moisture from the soil seeping in and rotting them as well as chemicals leaching from them into the soil.  We have not lined the beams and they're fine.   Some are now 4 or 5 years old and some were new last year after we had to replace ordinary pine planks painted with Cuprinol and which finally gave up the ghost and rotted after about 12 years. 

I'm surprised that there was nothing on the website when I ordered it saying that it had to be lined - after all it was sold as suitable for growing vegetables - and if it has to be lined to grow vegetables shouldn't they have supplied the lining? - after all without the lining it's obviously 'not fit for purpose'.

It's your call Dovefromabove.  Pressure treated wood has rather nasty chemicals in it.  That does not make it 'unfit for purpose'.  If it wasn't treated against rot you would have to do it yourself. Use compost bags to line the beds, they are pretty strong.

Depending on high the raised beds are you will find out they dry out very rapidly if they are not lined, and as been mentioned above the wood will rot more quickly, as it surely will.  If you enquire specifically you will find the wood preservative protection is not guaranteed for very long.  That is the nature of the beast!

I've got some heavy duty plastic to line the sides of the raised bed - still think it's a bit misleading for the company selling them not to mention the need for this until you've got the kit home and unwrapped!

I may have a word!