SFG raised beds directly on course gravel?

luke3026December 1, 2008

Newbie with a question -- The site we've chosen four our first SFG (actually the ONLY suitable spot on our property) is then edge of a section of course gravel. I've dug down a bit, hoping there was soil just a few inches below, but the gravel seems to extend at least 8+ inches down. So what issues would I face if I were to just construct raised beds directly on the gravel? I've searched a bit on the web and couldn't really find a yay/nay on doing this. I guess I'm just trying to avoid the laborious work of digging up (and then finding a place to dump) all the extra gravel. Would also need lots and lots of fill soil to fill the hole too. Any suggestions?


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I'd construct my beds a bit deeper than 6" in your case. The gravel should provide excellent drainage, but you might be required to water more frequently. If you are really in doubt, why not start with one 4x4 bed and experiment for a couple of months before making a decision on whether or not it will be what you want. JMHO


Here is a link that might be useful: Annie's Kitchen Garden

    Bookmark   December 1, 2008 at 11:26AM
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engineeredgarden(7, nw Alabama)

Luke - Leaving the gravel in place would be a plus, in my opinion. Your drainage will excellent. I would build the box on top of the gravel, then install landscaping fabric on the inside. After that, fill it with soil and you're set!
Like Granny suggested, you may have to water a little more frequently, but the pros would certainly outweigh the cons. Also, i'd lean more toward 8 or 10" deep....like granny pointed out.

Welcome to the sfg community.


    Bookmark   December 1, 2008 at 12:10PM
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mike_in_paradise(6U 5A Cn Jun9Sep29)

One of my gardens is like that and

First I screened out some of the gravel down about 6 inches.

and then I mixed peat most with the gravel below grade to try and improve the soil.

In a 4x8 box, 8 inches deep I ended up using 3 x 3.8 cu ft bags of compressed peat moss.

    Bookmark   December 1, 2008 at 1:28PM
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We were already thinking along the lines of using 2x10's for the boxes so that'd be 10" depth. I'll try to get a photo or two posted so you can get an idea of what I'm up against. I wouldn't mind the labor end of digging out the gravel, it's more the expense of getting some clean fill to bring everything level again.

    Bookmark   December 1, 2008 at 3:47PM
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engineeredgarden(7, nw Alabama)

luke - just a little helpful information for ya....a 2x10 is actually 9-1/2" wide.... Sorry, I couldn't help but tell ya that. :)


    Bookmark   December 1, 2008 at 3:59PM
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sinfonian(U8b A2 S5 SeaWA)

My beds are about 12 inches right on top of gravel on purpose. My landscape fabric is under three inches of gravel. So you should be fine with either direct dirt on gravel or a layer of landscape fabric between the soil and gravel. Up to you. There is no one right answer, thought adding the fabric would provide more weed protection.

I don't think you need to worry about anything needing more than the 10 inches of soil you're planning. Good luck and enjoy your garden!

Here is a link that might be useful: Sinfonian's garden adventure

    Bookmark   December 1, 2008 at 4:04PM
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jbest123(Zone 5 PA)

Hi and welcome, I would say it depends on if you have a local population of red worms. If you do, I would do every thing possible to encourage them into the beds that would include removing enough gravel to provide a continuous soil path to the base of the beds. It would also mean no weed barrier paper or cardboard is ok but no fabric. Those little red wigglers are as important as any thing else, you can do for the garden.


Here is a link that might be useful: Johns Journal

    Bookmark   December 1, 2008 at 4:10PM
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I wouldn't worry a bit about building the beds over that. As I said before, deeper than 6" (but I think all beds should be deeper). You already have some vegetation peeking through, so there's some soil right under the gravel. Like EG said, good drainage.


    Bookmark   December 1, 2008 at 5:04PM
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I'm with granny on this one, I'd built it on top of the gravel. 9 1/2" will work out nicely and the gravel will create great drainage. 8 inches of gravel!!! Someone REALLY didn't want to do any weeding on their property, I take it, lol.

    Bookmark   December 1, 2008 at 7:58PM
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If you want to get rid of some rock, you can try posting it on your local Freecycle or Craigslist free section. You might get someone who will come over, dig out and take away some of it. I recently did exactly that to get some rock for a pathway (the red rocks) portion of a project we did this summer/fall.

(click to enlarge, there are other photos on web album if you want to look...) From 2008 Backyard project

    Bookmark   December 1, 2008 at 10:29PM
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I think I'm going to try to dig up a small patch to really get a feel for how deep the soil is underneath and how much fill we'll need to fill the gap, and then take it from there. We're trying to do this SFG on the cheap since we're both currently laid off, but on the other hand I'd really like to get it installed correctly too.

Thanks for all the help!

    Bookmark   December 2, 2008 at 6:30AM
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Like the gravel idea. I bet it will drain well. Water sits on top of the clay here for what seems like forever!

    Bookmark   December 2, 2008 at 7:04AM
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After digging around a bit, I've decided to take the advice of just building the beds on top of the gravel. Seems like the easiest/cheapest/best option. I'm really looking forward to getting a SFG going. My wife and I have talked about growing our own veggies for years, but conventional gardening just seemed too overwhelming, requiring room we don't have, etc. And being technical by nature, I love the orderly-ness of the square blocks. And maybe the kids will be more inclined to eat their vegs if they're involved in growing them. I can hope at least!

Thanks again, everyone!

    Bookmark   December 2, 2008 at 4:48PM
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engineeredgarden(7, nw Alabama)

Luke - your comment about being technical by nature, and really liking the orderly presence from the grids reminded me of myself. LOL. I'm a complete neat freak! I think it's good that you get your children involved, I wish that I would have discovered this method while my children were small......


    Bookmark   December 2, 2008 at 5:03PM
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sinfonian(U8b A2 S5 SeaWA)

Luke, several points. First my 4 year old's favorite snack is to go out and pick a carrot from daddy's garden. He planted them and loves the fresh flavor.

As for being out of work, my condolences. Of great interest to me is the idea of gardening on the cheap. For you, I'd recommend checking craigslist or freecycle for wood for your beds. Go with scraps and use your time, sweat equity and technical skill to make it work.
Then for soil, go 100% compost from yours and your neighbor's yards, unless your municipality has free compost available. If you start essentially lasagna gardening now and chop the diverse ingredients fine (utilize up to 25% free starbucks grounds for your garden), your soil should be ready for spring planting.

I know you didn't ask, but I thought the concept of free would be of interest.

Best of luck!

Here is a link that might be useful: Sinfonian's gardening adventure

    Bookmark   December 2, 2008 at 8:42PM
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It's the best things for kids!!! I've got the 1yr and 4 yr old eating lettuce, zucchini and broccoli. The 1 yr old would bring me yellow pear toms that she picked off the plant and repeat, "Bite? Bite?" If nothing else it's a great science lesson for them.

    Bookmark   December 2, 2008 at 9:14PM
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Thanks for the advice Sinfonian! I'm keeping a lookout on the free boards looking for things I can use. Also just started a compost bin of our own for the first time. Luckily I have a few 2x10's leftover from another project that I can recycle. I didn't realize Starbucks will give you the spent grounds -- I'll have to stop by and check that out too!

    Bookmark   December 3, 2008 at 1:02PM
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