drainey0
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Concrete 6 inches beneath soil affect my raised bed?

so the other day i was digging around in my yard and noticed that basically all over the yard when i got down to about 6 inches of soil i would hit concrete literally everywhere. from what i have read this is what builders do to cheaply level out the land around the house then they throw top soil on top of it to cover it all up.

My question is this: I'm putting a raised bed in and filling it with good quality dirt/ compost, should i be worried about the concrete underneath making my vegetable toxic to eat? the raised beds are about 8 inches in height.

PaulF
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Re: Concrete 6 inches beneath soil affect my raised bed?

Probably not toxic but very difficult for growing a garden in six inches of soil with limited drainage because of the concrete. Like a small pot. Roots need deeper soil than that to do well.
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imafan26
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Re: Concrete 6 inches beneath soil affect my raised bed?

Yes people build raised beds on concrete and mine is made with hollow tile walls. It has not been a problem. Make sure your bed is in full sun. Ideally it should be no more than 4 ft wide or less so that you can reach accross it without having to step in it. Make sure you have access from all side so not up against a fence or a wall. If you plan to grow tomatoes, beans, peas, gourds, cucumbers, anything that would need a trellis. Make the trellis around 6- 7 ft high. I would put a step on the back of the garden to be able to reach to the top of the trellis. Make sure it is wide enough for safety. Put in a permanent trellis on the North side of the garden. The best alignment is north/south Tall things and trellis will go on the North end. A bed with dry laid concrete tile stacked 2-3 tiles high from the base and reinforced with rebar will give you a bed 16- 24 inches deep. Fill the holes with a layer of gravel and dirt on top if you want to plant in the tile holes, otherwise fill them all with gravel and cap the tiles if you want a finished top.
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rainbowgardener
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Re: Concrete 6 inches beneath soil affect my raised bed?

I agree, your worry isn't toxicity, it is that you don't have enough soil. But you can build a raised bed on top of what you have. With your 6" of soil, plus another foot on top of raised bed, you will be fine.
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drainey0
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Re: Concrete 6 inches beneath soil affect my raised bed?

Well the bed is only 8 " tall so all together I would have 1' 2" of dirt space and I'm growing tomatoes and pepper in it

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rainbowgardener
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Re: Concrete 6 inches beneath soil affect my raised bed?

Not ideal, but will probably work. Just know that with that little soil, it is like a container and you will have to fertilize more. Check your soil for moisture regularly. It could dry out faster because not a lot of soil or it could stay wet too much because no where to drain down to. So you will just have to see.
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applestar
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Re: Concrete 6 inches beneath soil affect my raised bed?

Yes. This will be just like a container and you will be limited in number of plants -- especially tomatoes -- you could grow. How big will the raised bed(s) be and what variety tomatoes and peppers are you going to plant? Planting spacing will depend on their mature size. They will also need a lot of water when in fruit.
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imafan26
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Re: Concrete 6 inches beneath soil affect my raised bed?

Tomato roots can go down more than two feet and will spread sideways as well. It is easier to space them too. In a small garden large plants take up a lot of the space and it more efficient to save that space for plants that take closer spacing like lettuce, beets, radishes. only 2 tomatoes will fit in the back of a 4 ft wide box if you trellis it up. It still needs a couple of feet in front of it because tomato vines need to be continuously trained and the suckers are going to fall. unless you keep cutting them off. Peppers can be planted 12 inches apart but 18 inches is better for air circulation.

I have 3 -18 gallon buckets for tomatoes.outside of the veggie garden. It takes up about 10 linear feet. I have 7 FT high x 12 ft long CRW. The ends of the fencing are wrapped around the end buckets forming cages with the third buket with the fencing in back of it. I have given them more space as I have room to get between the buckets for weeding and picking the tomatoes.
Anything that is goin over 2 ft probably has a root at least that long. Vines can be grown in a raised bed but you will have to either train them up or let them sprawl outside of the garden.

Asian greens, lettuce 8-10 inches
beets, spinach 3-4 inches
green onions, carrots -2 inches
onions 3-4 inches
cucumber - 4 in a hill with a vertilcal trellis. I stack two tomato cages and reinforce them with long stakes. depending on the size of the trellis it can be as small as 1 square foot.
Broccoli, zucchini, kale, cabbage, bush cucumber, bush squash 30-36 inch circle
Corn in a block of at least 4x4 dimension. 8-12 inches apart.
Happy gardening in Hawaii. Gardens are where people grow.

drainey0
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Re: Concrete 6 inches beneath soil affect my raised bed?

yea im very limited on space and sunlight area.,..... next year ill add another 2x2 box on top of the box i already have to get a total of 24 inches of soil depth. would buy the huge pots to grow stuff in but there like 40 dollar a pot.......... sooooo im stuck with the lowes bucket....... cucumber are growing really well in the lowes bucket had a tomato plant in a lowes bucket but it died on me due to me being out of town and not being able to water it anmd the rain that was suppose to happen didnt so yea............................... ive got 3 tomato plants and 1 pepper plant growing in the 2x2 box right now and they seem to be doing really really well.

imafan26
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Re: Concrete 6 inches beneath soil affect my raised bed?

I use muck bucket on sale they can be $4-$8. The go on sale in summer often and are used as party tubs. I use a soldering iron to make hole in plastic containers. Less damaging than a drill. I you want you can make a self watering container with an 18 gallon rubber maid container. It will hold one tomato but you still need the trellis.

https://www.postoilsolutions.org/documents/Earthbox.pdf

Most vegetables need a minimum of 6 hours of sun. If you don't have that much reconsider the plants you want to grow and grow ones that can do better with less light. like mints, chives, green onions, spinach, strawberries. Fruiting plants usually need a lot more light.
Happy gardening in Hawaii. Gardens are where people grow.

drainey0
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Re: Concrete 6 inches beneath soil affect my raised bed?

well im getting like 8 hours of sunlight in the area that box is in but like i said there is cement under it and then rest of the area that i can get sunlight is on concrete drive way so im using the lowes buckets for that. everything seems to be doing really well....... and water inst pooling up in the the raised bed i made so thats good.

bobbyg
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Re: Concrete 6 inches beneath soil affect my raised bed?

I have no personal experience but isn't Mel's square foot gardening book says that 6" is plenty for most of the stuff. I do know the tomatoes roots are deep and you would need more depth for carrots. But for lot of stuff it should be ok. If you could, I would raise those beds so I can more soil into them. For my buckets I put a drip system with a timer, now no more complaining from the wife. And no need to worry when you out of town. It was not that hard to do.

BTW - Why would builder have concrete and then top soil to cover it? That will cost them more money IMHO.

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rainbowgardener
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Re: Concrete 6 inches beneath soil affect my raised bed?

Mel's square foot garden book does indeed say 6" tall. But that is 6" on top of decent natural soil. AND many of our members have written in to say in their experience six inches is not enough, even with soil under it. Just because someone writes it in a book doesn't mean it will work for you! :)
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