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Constructing Raised Beds - What to line inside with?

Posted by james_t (My Page) on
Sun, Aug 15, 10 at 12:56

I am constructing two 4'x18' raised beds to start a vegetable garden. I have everything planned out except what to line the inside of the frames with to protect the wood from the wet dirt. On the ground I will be placing 2" of crushed gravel to provide drainage underneath.

Can someone provide some suggestions on what to use? I want to prevent the wood from rotting as much as possible. The boxes will be constructed with untreated pine.

This is how I will be constructing my garden if anyone wants to supply any other tips:

1) Till and level area
2) Install galvanized wire over ground (we have burrowing rodents)
3) Place 2" of crushed gravel over ground
4) Build raised bed frames, 2"x10" double-stacked for 20" high beds
5) Remove some gravel from inside beds to allow worms to make their way inside
6) Install drainage material on inside of beds
7) Place loam in raised bed
8) Install soaker hoses, 3 evenly spaced down each bed
9) Start planting
10) Eventually install fence to block off remaining area from animals

Thanks for your help.


Follow-Up Postings:

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RE: Constructing Raised Beds - What to line inside with?

Hi, what zone are you in? Sounds like you have a respectable plan.


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RE: Constructing Raised Beds - What to line inside with?

1) putting crushed gravel on the ground does not improve drainage. it will actually reduce drainage and keep the water above the gravel. I know it is not logical, but water has trouble moving from one type of soil to another. In this case soil to rocks. the old advice of putting rocks in the bottom of potts to aid drainage is no longer good advice.
2) I doubt that lining the wood will reduce rot. If you want to keep water off the wood you would need to use some kind of plastic. but if you use plastic water caught between the wood and plastic will never dry out leading to an increase of rot.
3) 2" pine in zone 5 will last 7 years or so.
4) I would make the bed only 10" heigh. Heigh beds heat up more and need more watering. Instead you can dig a hole and fill it with better soil, or just use your current soil. You want roots going under ground level where is is cool and where there is more water. it is also half the price, making rot less of an financial issue.


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RE: Constructing Raised Beds - What to line inside with?

My experiences chime with madtripper's points: when I made raised beds with untreated pine, some were lined with plastic and some left without. The beds with plastic are rotting much faster, as water is trapped against the wood.
"build raised beds" seems to be the standard advice, not taking different situations into account. I garden on sand and raising my gardens above ground made hydration a real battle. I've been lowering my beds ever since. The raised sides make excellent windbreaks for seedlings!
Of course there are factors such as disability and unforgiving geology that make raised beds necessary and useful, but I think the cons generally outweigh the pros.


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RE: Constructing Raised Beds - What to line inside with?

I am in zone 6-7 (Massachusetts).

I can't have plants growing in the ground, the soil is bad and not suitable for growing vegetables. That is why I want to build it double high.

In some places there is concrete buried an inch or two below the soil. That is why I want to put down gravel, otherwise in a heavy rain it turns to mud and the water has no where to go.


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RE: Constructing Raised Beds - What to line inside with?

I lined our raised veg beds with weedmat. It stops the couch and kike from invading the beds and also helps to retain moisture in the bed for longer in summer.

I have used a hardwood though, not pine.

If you are only looking at something to try to preserve the timber, then I think I wouldn't bother to line. Have you checked with a hardware store to see if there is a timber preservative that is safe to use in a veg garden?


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RE: Constructing Raised Beds - What to line inside with?

This brings to mind instructions I had years ago for making window boxes. It was stressed to paint the entire inside of the box with TAR and let it dry thoroughly before adding soil. I believe this would work for your raised beds, as well.


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RE: Constructing Raised Beds - What to line inside with?

I'm pretty sure annual veg roots aren't going down beyond 9.5" (the actual height of a 2x10). If you're doing asparagus or something, that may change the equation. And as mentioned above, don't do gravel "for drainage".


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