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

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.

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.

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?

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.

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".

Thanks for all the info above, particularly the advise about NOT LINING the beds and NOT putting gravel. I already had a configuration of raised beds in my center city Philadelphia (zone 7) garden/ backyard and they were rotter (40 years old) and I needed to rebuild them. I used cedar 4x4 and I decided to make them slightly taller (15inches) because I cannot bend and because underneath the existing beds there is only another 2-3 inches before the cement foundation. I don't have enough sun for tomatoes but I can grow some other veggies and perennials like hostas and hellebores and I want to have a camellia and some other stuff that needs more earth

You mentioned that the soil dries faster in higher beds and the drying of the soil concerns me a bit. However since I don't have much sun it might not be a problem perhaps? Please share your expertise

thank you

Absolutely do NOT tar or use a preservative on any of the wood. The chemicals WILL leach into the soil.

I too am planning raised beds-but they will be the back of seating on a deck, so it will be about 48” high, 18” wide for about 8’length. Thinking cedar, waiting for estimates. I did find a product that might be helpful for this discussion (to follow), but now I am worried about that height. I am outside chicago, zone 5b. I was going to keep bottom open to have contact with ground. Now I’m thinking perhaps I should have drop in liner boxes instead?
I’d appreciate any input. Will be planting flowers, hoping for mix of perennials
For those looking for a way to seal inside of planters, this sounds great ! But haven’t used it,so can’t give a firsthand referral.

PLANTER LINER PRODUCT:
I am reaching out to you in regard to your planter situation.
We have a product which is our” Primer Free membrane “ that I believe will be a great solution for your needs.
This product will allow for moisture to escape through the product while protections your wood structure. This product is available in 36” x 50 ‘ rolls which will reduce the amount of overlapping you would need to do.
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I guess the only way to prevent rotting of the sidewall on a raised bed would be to use plastic lumber to build build it? The problem with plastic lumber might be that the PVCs would leach into the soil and get into the vegetables? I do not have proof of that.

Plastic lumber needs more lateral support than regular lumber. It doesn’t have the same strength as to sideways pressure. If you are using untreated pine, just plan to replace it periodically.

If there is concrete buried a few inches below the surface that is preventing water from percolating down into the soil, how is putting gravel on top going to help water percolate down into the soil? That doesn't make any sense to me.

Please realize that if that concrete covers the ground area under your raised bed, your raised bed is going to function more like a giant container garden.

It's a fact that sometimes, raised beds are undone. I can't see that a layer of gravel will be all that much of a help for drainage (though I don't fully accept that it will harm it either.) But it would surely make it a lot harder to clean this project up when and if ever the time comes. I would go sans gravel.

Also, I know you already have a plan for making the container out of wood, but it's the case that many wood boxes end up looking pretty shabby down the road. I recently came across a video where someone made raised beds out of interlocking precast concrete panels that they fabricated themselves. ((Link to precast raised bed panels.)They were much nicer looking than the typical wood affair and are also flexible in that they can be linked to create larger size beds. They'd be much more durable, too. If ever undone, they could be reused somewhere else instead of being pitched in the trash. No need to worry about rot or coating the insides.

Wow, I just saw that this is a nine year old thread that someone resurrected. Westes, what gives? :) You already have your own thread about your raised beds..

@illsstep I answered a question posed by this thread, which had nothing to do with the questions in my thread.

Build your raised beds with cinder blocks that don't rot.

Based on my experience, I advise to use a natural barrier for the bottom of the raised garden bed. Like you said, if you have burrowing rodents definitely you'd wanna lay the bottom with a metal wire for protection. Anyways, I found this article helpful in deciding what to put on the bottom of my raised garden bed: https://lifeofplants.com/raised-bed-gardening/liners/

Based on my experience, I advise to use a natural barrier for the bottom of the raised garden bed. Like you said, if you have burrowing rodents definitely you'd wanna lay the bottom with a metal wire for protection. Anyways, I found this article helpful in deciding what to put on the bottom of my raised garden bed:https://lifeofplants.com/raised-bed-gardening/liners/

https://lifeofplants.com/raised-bed-gardening/liners/https://lifeofplants.com/raised-bed-gardening/liners/

Im

I am making raised beds that do
Not sit on the ground. They are cedar boxes and the bottom of the box is cedar as well. Do I add fabric liner? And drill holes for drainage? The man building them is installing black rain gutters underneath to catch the drainage so it’s not on the deck. How many drain holes are recommended and is lining it with fabric safe and recommended?

I am doing the same thing! I call them “elevated” raised beds. They are made of cedar & not sure if liner is needed. Anxious to see the responses.

If you seal the bottom of a raised bed off from the ground underneath - as you have done by building boards at the bottom of the planter with drainage holes in them - then you have a container, not a raised bed. That's important because a container imposes special restrictions on the kind of soil you can use. Putting in normal potting soil, topsoil, or garden clay, is going to create significant drainage problems for the plants in that container. If you do not mind that, when you get ready to plant put up a post on the container gardening forum and start a discussion about a good kind of soil to use in a container for the kind of plant you are raising.