Cedar Raised Garden Beds

Cara Baxter
13 days ago

Hi all!

Really hoping for some helpful advice. I’ve been trying to find a cut and dry answer to my question, however I am having a hard time finding one.

I am going to be building multiple 18 inch wide, three feet high, six feet long cedar raised garden beds to act as a “fence” in my backyard to corral my little ones. I am very excited!!

My main question is what do I put at the bottom of the bed? We have chemically treated our lawn in the past, and to be honest, my husband will most likely want to continue this practice. I do not want any of the chemicals to get into my organic garden. I’ll be growing fruits and vegetables. I’m nervous if I only use newspaper, cardboard, or even wood, that eventually it will decay and the chemicals will work their way into my soil and therefore my vegetables. Would I have to use plastic? I’ve read that using plastic can make the wood rot faster and cause drainage issues. Plus I don’t know how I feel about plastic possibly leaching chemicals into the soil either. And if I cannot have my garden soil directly on my native soil, do I need to use a potting mix instead of making my own soil/compost mix? I plan on having at least 24” of growing depth, 36” if I can safely have my soil touching the ground. I’m so confused!! I really need some advice. Maybe there is no perfect solution, but I’m determined to find one! Any experience/expertise is welcomed!

Thank you!

Comments (22)

  • laceyvail 6A, WV

    But your children are playing on the chemically treated lawn!

  • Cara Baxter

    @laceyvail I’m asking about my cedar bed, not lawn options. They only play after its been a few days

  • floral_uk z.8/9 SW UK

    Chemicals used on the lawn will render your vegetables non organic by definition. Anything leaching into the bottom of the boxes will be insignificant by comparison. If a few days is considered a sufficient time buffer to allow the children onto the grass why would you need to worry about chemicals applied months ago beneath the beds? What we're trying to say is that your concern is directed to the least important issue.

    So, to answer your question, just put the beds on the ground.

  • Cara Baxter

    After a few days, aren’t the chemicals off the grass but still in the soil? The kids do not eat the grass or dirt. I don’t understand why the chemicals leaking in through the bottom of the box would be insignificant... we do not spray the lawn, so I’m not worried about wind carrying anything. What we normally use is a four step lawn program that consists of fertilizer and helps to prevent weeds. Even if I used organic top soil and compost? I’m not using my soil for this but getting it brought in from my local organic farmer. Of course I would prefer to not use any chemicals on the lawn, but I don’t know if I will be able to win that discussion. And besides, if it’s been used in the past and we stop using it going forward, isn’t it still in the soil? I understand this isn’t a perfect scenario, but I’m trying to do the best option working with the options I have.

  • floral_uk z.8/9 SW UK

    Read the label on the product you use. Google the ingredients. Do they persist in soil? If they don't last on the lawn why do you think they'd last in the soil?

  • Jamie

    Just take a deep breath, relax and build your deep garden beads. Fill it with your container mix of choice and plant. You will be fine. Your vegetables will be fine. Your kids will be fine.

  • Cara Baxter

    I thought that they would get rinsed off the grass blades and go deep into the soil. Maybe I’m wrong? I am in no means an expert in lawn care. Do you have any no chemical lawn options to offer? Still also looking for an answer to my original question regarding the bottom of my raised beds. The beds are functioning as my fence, so planting directly in the ground isn’t an option. If we switched to organic lawn care, isn’t there still concern for previous years chemical fertilizer use? Thanks for the help

  • floral_uk z.8/9 SW UK

    Read up about the chemicals you have used. We don't know what they are do we can't comment on persistence in the soil.

    I answered your original question about the bottom of your beds. I said 'just put the beds on the ground'. If you have burrowing pests you can put wire netting underneath.

  • Cara Baxter

    Putting them on the ground isn’t an option I would like to do, but thanks for your input

  • gardengal48 (PNW Z8/9)

    Floral's comment was intended specifically to the beds (not the actual planting)......they can be seated directly on the ground. No plastic required :-). You do want to remove or kill off the lawn first. Just remove the sod and roots or smother with cardboard and newspaper.

    With very few exceptions, lawn chemicals breakdown very rapidly after application. So soil persistence (aka soil half-life) is typically pretty short - a few days to a few weeks. Exposure to sun, water and soil biology neutralize or render them pretty much harmless after a relatively short period of time. There are exceptions but they are rare. Research what has been applied to know for sure. And with 3' deep beds, you really have nothing to worry about. Your vegetable roots are unlikely to penetrate down that deep to reach potentially contaminated ground soil and any potential contamination will not migrate upward through the soil

    As to the "gardening organically" long as you avoid any further application of synthetic fertilizers or pesticides, you are growing organically. It is only if you want to be certified as an organic grower that you have wait a set amount of time (3 years).

    And I would encourage you to pursue organic lawn care practices. Not just because they are organic but because they release or leach a significantly lower amount of chemicals (everything is a chemical) into the environment and our waterways. Lawn care is the source of much of our water pollution.

  • floral_uk z.8/9 SW UK

    Gardengal is right about my meaning. I said place the beds on the ground. I didn't say plant in the ground. Sorry if that wasn't clear.

  • Cara Baxter

    Floral_uk, yes you did! I’m sorry, I misread that.

    Gardengal, good to know about the soil half life! Thanks.

    And to all, I think I am going to push to switch to organic lawn care this year. It is a concern of mine using the four step programs... and to be honest, the lawn gets pretty brown anyways. Maybe something else will be better!

  • PRO

    I don't think you're going to get an answer, here, based on the scientific, laboratory study you're hoping for ... unless there is a soil scientist/chemist in the audience, and such a study has been done. Our answers will be based on the practical "gut" hunches that gardeners, horticulturalists and landscapers would have. My hunch is that your best bet of accomplishing your goal is to merely have a high height depth of soil in the raised bed. And I think 3' is adequate. If you place a permeable barrier at the bottom of the bed, it will do nothing. If you place an impermeable barrier there, it will destroy the bed by inhibiting or preventing drainage.

    The vast majority of garden plant roots are going to be in the top foot of soil. Some roots are going to go deeper, but probably not many roots, and only of the largest plants (that you likely would not have) are going to go to 3' depth. Lawn chemicals in the soil are going to degrade after application and move downward. They're not going to move over into your raised beds and go upward. The likelihood of your raised garden bed plants coming in contact with the "tainted" lawn soil seems very small to me, not enough to worry about.

  • Christopher C Nc

    Cut and dried: Place the raised beds on the ground without any barrier between the native soil and your planting mix.

    Next: Make a three to four foot wide path along your raised bed 'fence' of mulch, gravel, cement, whatever suits your fancy. You now have a barrier that will not need lawn chemicals.

    Your husband can have his toxic lawn and you can have your organic produce. Everyone will be happy. Design wise I can't vouch for the look without knowing more about the site and setting.

  • Cara Baxter

    Yardvaark, you are right! So I called to find out. The longest time period for the chemicals to be out of the soil is six months. I’m glad to know that if I place them directly on the ground in the spring, I won’t have anything to worry about. Thanks for your input! I think I will push for greener alternatives this year, considering what we have been using isn’t working that great anyways!

    Christopher C Nc, haha I love your diplomacy!! I think adding some type of border would look very nice, but I don’t think I’ll have room for it. We are enclosing a relatively small space, and a three foot border will take away grass play space. Thank you for helping!

  • mad_gallica

    The bigger question is the construction engineering required to build it. If the box is filled with soil, after a rain that soil is going to weigh more than 2000 lbs.

  • Embothrium

    Also there will be the materials cost of cedar boxes 3' high.

  • Cara Baxter

    I already have plans and materials configured for this project. Math major here! And my husband is an engineer. These are “fun” projects for us to figure out :) Using cedar fence posts are a more cost effective way to build this instead of buying cedar planks. Plus, I’d rather spend a little more upfront and use cedar and have it last a long time.

  • Christopher C Nc

    Cara I bet your husband would enjoy a good mowing edge for his lawn. A sharp edge can make any lawn look better. Give a nice defining border between your fine produce and the lawn some thought in your design build project.

  • mad_gallica

    The problem with using fence posts is that the pieces have to fit tightly together or the soil just washes out through the cracks. Then you need the mowing edge to catch the river delta so you can put it back.

    Depending on where you are, and what exactly is 'cedar', it may not last that long.

  • Seabornman

    We put down a geotextile fabric (the heavy stuff) wider than our raised beds, then dropped the beds and soil on top. Next is either concrete pavers or gravel. We're trying to keep quackgrass out but I think that could be an approach for you. The fabric lets water out but nothing grows up through it.

  • Embothrium

    Success with landscape fabric depends on holes never being poked in it anywhere and anything that could form a substrate for weed growth never being allowed to remain on top of it. This includes decomposed leaves and clumps of potting soil or similar material. (And of course placing organic mulch on top of fabric becomes completely counterproductive once the mulch has broken down enough to start supporting the growth of weeds).

    Gravel used over fabric anywhere organic litter is blowing around or being dropped has to be kept groomed. This can quickly become a tedious operation.

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