Waterproof membrane in raised bed?

BouncingBack

Morning!

We had some raised beds built about two weeks ago, largely because the sides of the garden are damp and we can't do any more structural work to improve drainage. While the beds were being constructed, we had some very heavy rain and the wood looked wet (it is treated wood) but I thought it would improve when the weather dried up. I've planted mature ferns at the bottom of both beds as they're at the bottom of a gentle slope and don't get much sun. One of the beds, however, is still damp only on one side right at the bottom (see pictures). Should I dig out the soil and fit some plastic sheeting against the wood on the inside, just on that section? I suspect the water is also coming up from underneath too, but there's nothing I can do about that now. Concerned that it's this wet and we're not even in winter yet... 

Thanks!

februarysgirl

I lined mine when I put them together.



It was recommended by the manufacturer (Woodblocx) to extend the life of the timber.

This is what I used https://www.amazon.co.uk/gp/product/B00CBUGFMO/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Fire

I line my raised beds generally. I use old compost bags. Make sure to make drainage holes.

Pete.8

My only thought would be that if you have plastic against the wood there would be always be condensation between the plastic and wood that keeps the wood damp all the time as it can't breathe.
I have several raised beds and didn't line any of them.
The sleepers used were pressure-treated.
Time will tell..

BouncingBack

Pete.8 said:

My only thought would be that if you have plastic against the wood there would be always be condensation between the plastic and wood that keeps the wood damp all the time as it can't breathe.
I have several raised beds and didn't line any of them.
The sleepers used were pressure-treated.
Time will tell..

This is my worry too and it's probably why the (very experienced) landscaper we used didn't line it. Very concerned it's this wet already though. Had a look and the one at the other side is too. Unsure how else to improve the situation. 

BobTheGardener

Don't worry about condensation - wet soil in contact with wood will cause rot really quickly, so i would line at least that corner with plastic.  All of my beds are lined with old compost bags - those I didn't line have all had to be replaced..

BouncingBack

BobTheGardener said:

Don't worry about condensation - wet soil in contact with wood will cause rot really quickly, so i would line at least that corner with plastic.  All of my beds are lined with old compost bags - those I didn't line have all had to be replaced..

Ah ok. So my next question is how do I do it now they're filled, mulched and planted at the bottom? Also, thirsty plant recommendations (other than hostas which I've fallen out with) that do well in very moist soil with fairly small amounts of sunlight, especially in winter, would be greatly appreciated. My plan for the side posted above was flowers, but it might have to be more functional than visually appealing given just how wet it is. The top of both these side beds gets a lot more sun than the bottom, hence the ferns there.

Fire

Some of the ferns, heucheras and hellebores should be fine there, I would say.  Maiden hair fern out like it - Adiantum venustum.

https://www.plantsforshade.co.uk/acatalog/Adiantum-venustum.html

Your sleepers are pretty thick so I don't think they'll rot away any time soon. I had some planters made of fairly thin decking materials and they lasted well for ten years (with wood preserving on most of the outside applied every few years). They were much thinner than yours, but not in shade and not in a always-damp area.

BouncingBack

Fire said:

Some of the ferns, heucheras and hellebores should be fine there, I would say.  Maiden hair fern out like it - Adiantum venustum.

https://www.plantsforshade.co.uk/acatalog/Adiantum-venustum.html

Your sleepers are pretty thick so I don't think they'll rot away any time soon. I had some planters made of fairly thin decking materials and they lasted well for ten years (with wood preserving on most of the outside applied every few years). They were much thinner than yours, but not in shade and not in a always-damp area.

On it with the heucheras already, have three at the other side along with the large fern and a sarcococca! Thanks for the link, I'll have a look.

We have a very large bed at the top made from the same sleepers which has never been wet as it's at the top of the slope and gets full sun. Should I just try my best to very carefully not disrupt the plants and dig out just enough to get some sheeting against that bottom chunk? 

Slow-worm

You could line the bottom, which would involve getting the soil and plants out. 
If it's any help, my raised beds aren't lined, they're mostly old railway sleepers with a couple of new ones - they've been there around 20 years (way before we moved in) and the only little bits that are rotting appear to be from insect/bird damage. They stay wet most of the winter as they're around the lawn.

Arthur1

I garden mostly using raised beds and never line. It would have to  be done very thoroughly to keep all the water out.