You could use food grade plastic liner. Redwood should hold up,for a long time without any protection though.

Sorry, ignore the previous response by me.

I meant to make a new post, not a response.

Does anyone know how to delete one of your own posts?

Em, unfortunately there is no way to remove a post on these forums. Only the moderators can remove threads.

I'm also very interested in this concept and hope someone could share some experience in lining insides of wooden containers. I need to replace some pine boxes painted inside and out with oil based polyuethane paint. All the boxes I built like this only lasted 5 years while boxes I built using that treated wood have lasted 10 years and look like they'll go another 10. My treated wood boxes do not support anything edible. The new boxes I need for replacement next season will support veggies -- thus my concern.

I'm toying with the idea of lining the inside with that rubber roof material used for flat roofs that you can buy in rolls at Home Depot. I don't know, however, what kind of nasty chemicals that will leach out of that material and into the veggies. With a torch and a little practice you should be able to line the inside with this material rather easily. And that rubber is rather durable, it has to be to protect a roof from all the elements. But this is theory since I haven't done it. I do have a flat rubber roof so I somewhat know how to handle that rubber even though I hire people who know what they're doing to actually install this on my roof. The planters I think I might be able to handle.

Any other hints about lining material would be helpful.

We have raised gardens with vegetables at work using pressure treated wood lined with vapor barrier poly. The soil has been tested regularly for contaminants and none have been found.

Thanks for all of the relevant responses.
I have lined previous boxes with poly sheeting. The problem is that some have started leaking ( I must have punctured them after planting ) and any plastic that sits above the soil starts to break apart into little pieces.

Do anyone have knowledge about pond liners? I thought that this material would not leach any toxic chemicals given that people put fish in their ponds

I have used a pond liner to line wooden containers, but don't have any info regarding possible leaching. I just thought that they may be ok if fish should survive...just like you said.

I did not grow any veggies in it. But it worked great. I used it for a bog garden (lined bottom as well), and also for planting perennials (lined just the sides).

I always put a strip of wood on top edge of any wooden container for couple of reasons:
1. it will give it a 'finished' look
2. keeps any 'lining' material & the wood the box is made of from being constatly wet (from rain &/or watering), and from sun damage.
(Learned to do this hard way-exactly same problem you described with poly liner breaking at the top.)
I also cut this strip on 15-25degrees angle to get better water runoff.
(BTW, wooven poly is better than regular, more resistant to tearing).

Rina

Modern pressure treated wood is not the same arsenic based wood from decades ago. It is safe to grown in. If you are really worried, you can always look for some lumber treated with acetic acid.