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Thread: Soil mixture for raised beds?

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    Default Soil mixture for raised beds?

    Hello all, new to Alaska raised bed gardening. Planning on building raised beds from 2x12 lumber (is it ok to use treated or should I stick with cedar or Trex?). Is 12" deep enough to grow most plants here?

    My main question, what ratio of top soil, compost, manure, etc. is recommended for Alaska gardening?

    Thanks for any help anyone can give.

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    Supporting Member Old John's Avatar
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    Quote Originally Posted by akpackfan View Post
    Hello all, new to Alaska raised bed gardening. Planning on building raised beds from 2x12 lumber (is it ok to use treated or should I stick with cedar or Trex?). Is 12" deep enough to grow most plants here?

    My main question, what ratio of top soil, compost, manure, etc. is recommended for Alaska gardening?

    Thanks for any help anyone can give.
    I can't help you with any specific ratio of top soil : Compost, but in my experience I don't think you can have too much Compost. Composted manure is great too.

    I've got raised beds made with both 2x10 and 2x12 and they each work very nicely for everything including root veggies. I used untreated lumber. I'll probably have to replace it in a few years. Hopefully not all at once.

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    Member Anythingalaska's Avatar
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    I have a raised bed made of two layers tall of cedar 2x6's. It has worked well for what I want out of a small garden. More lettuce than I can eat, green onions and leeks do great, same with Snap peas. I just used potting soil mixed with seeweed that I harvested locally and mixed into the soil.

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    I made a few 2x12 raised beds out of untreated lumber and they have worked great. If you are in the central peninsula area I would recommend this gentleman for compost: "TNT / Fritz Miller, 398-8851 locally-made compost and planting medium for raised beds"



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    Moderator Paul H's Avatar
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    As far as materials, I personally wouldn't use treated lumber as I don't want nasty chemicals in my food. If you use untreated 2X10's or 2X12's they will be falling apart within 5 years, ceder will probably last you twice as long. Trex is not designed to be in contact with damp soil, I don't know how long it would last but it will deteriorate in time. As far as soil depth, it depends what you're groing. I'd say 12" should be plenty for most items, you might want a bit more for carrots and you could probably get by with a bit less for vegitables with shallower root systems.

    What will be under your raised bed garden?
    Those that are successful in Alaska are those who are flexible, and allow the reality of life in Alaska to shape their dreams, vs. trying to force their dreams on the reality of Alaska.

    If you have a tenuous grasp of reality, Alaska is not for you.

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    Higher off the ground is better. Mine garden beds are waist high built from landscape block. No more leaning over to garden. The primary soil is local landscape topsoil and it's amended every season with sterile steer and chicken manure. Tent the boxes with black visqueen ahead of planting to warm the soil. Tent with clear visqueen for the first few weeks after planting and watch the plants go nuts. Our enemy is cool temps, especially in the early season. Overcome that and you'll have much better success.

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    Thanks for all the input. I will probably go with Cedar for the raised bed boxes. Wrapping the beds in black visqueen to soak up heat pre-planting sounds like a great idea.

    Under the beds will be native soil. I live in the Wasilla area so native soil is rocks, gravel and sand. I've seen some posts talking about putting some closed cell foam (blue board) in the bottom of the raised beds to insulate from the cold ground. Any opinions on that?

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    Supporting Member Old John's Avatar
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    Quote Originally Posted by akpackfan View Post
    Thanks for all the input. I will probably go with Cedar for the raised bed boxes. Wrapping the beds in black visqueen to soak up heat pre-planting sounds like a great idea.

    Under the beds will be native soil. I live in the Wasilla area so native soil is rocks, gravel and sand. I've seen some posts talking about putting some closed cell foam (blue board) in the bottom of the raised beds to insulate from the cold ground. Any opinions on that?
    I tried black visqueen once to attempt to preheat the garden bed.. Clear works much better... in basic terms I think it's because Black absorbs the heat where as the Clear transfers it.. It might work good to melt the snow faster... Just before breakup, I scatter the ashes out of my burn barrel onto the raised beds, this really clears the ice and snow quickly.. Then I staple a couple sheets of clear over the raised beds kinda creating mini green houses. and it does a great job. I have no advice on the Blue Board, except that like you, I live in the Wasilla area, and have just the native KGB soil under my beds and my gardens do fine.. depending upon the weather of course..

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    Member SwansonSilver's Avatar
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    Have you looked into "square foot gardening"? You only need 6" deep beds for everything but carrots and you use a mixture of compost, peat moss, and vermiculite. 1/3 each. A google search will turn up lots of info. We're gonna give it a try this summer.

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