bulldogboy
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new bed suitable for vegetables

Hi folks,

I was after another vegetable bed so I've just broken up about 10 square metres of concrete which i've disposed of.
What remains is about 3 inches of soil on a heavy clay base. The soil is interspersed with small pieces of half inch concrete. I intend to put about 6-8 inches of new soil on top. My questions are:

1) Could there be a problem with the ph of the remaining concrete?

2) Will the bed be deep enough as i don't wish to dig into the remaining clay?


Advice much appreciated :)

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applestar
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Re: new bed suitable for vegetables

I think concrete bits and powdered concrete from the removal could raise pH.
I think what must be firmly compacted soil base would be a problem. Can you at least fracture that -- you don't have to dig up, just break it up.

Here is a link to another member's success with a broadfork.
:arrow: Subject: How to break up rock-hard soil?

I have a tool called digging bar it is very heavy -- mine has a point on one end and a 3" wide flat "spade" on the other end. I use the pointed end to easily make 12-18" deep "pilot holes" for fence posts, but instead of pulling straight back up, you could use this like a lever to fracture soil.

Once the soil is fractured, you could spread compost or composted manure which will be washed down the channels made by fracturing. And the soil microbes and attracted earthworms, as well as plant roots will follow them down, If you are not planting right away you can use unfinished compost (if you have any) or incompletely aged manure which would be more biologically active -- but then you'd have to wait for 2-3 months.

6-8" is rather shallow so it will dictate plant choices. That and the pH issue. What were you thinking of planting? It's actually better to plant a more pioneering type deep rooted plants with less than ideal performance this first planting because the roots will help to break up and integrate organic matter into the subsoil.
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rainbowgardener
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Re: new bed suitable for vegetables

That soil will be pretty dead - compacted, with no air or water circulation for all the years the concrete was there. So no life in the soil.

I would do as applestar suggested re fracturing etc., but then I would build raised beds on top . I guess that is what you mean by the 6-8" of new soil, but you may need some way to keep the new soil in place. And I agree, 6" would be quite limiting. I would think about 8 - 12".
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imafan26
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Re: new bed suitable for vegetables

I agree that raised bed would be the way to go. Concrete can raise the pH but if your soil mix is acidic it can counter it. I built my bed with two tiers of hollow tile blocks. I have not worried about the leaching from the blocks.

My soil tested at a pH 6.4. I have use a lot of peat moss and I do not use chicken manure which will raise the pH a half point. If you choose materials for the bed that keeps the pH on the slightly acidic side, it should not be that big a problem. The concrete pieces will leach slowly over time. It would be a different story if your native soil was coral or limestone, you cannot fight that except with a raised bed or containers. It depends on what you are planting too. Blueberries would be happy with a pH of 5, tomatoes 6-7.5, cabbages and baby's breath like it more on the alkaline side.
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bulldogboy
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Re: new bed suitable for vegetables

Hey thanks everyone for your prompt feedback.

I forgot to mention that i have aerated the clay with a garden fork and I'm looking at constructing a border of medium sized basalt rock. After another look, the finished depth would probably be about 8-10 inches.

I was planning on putting tomatoes in. As they don't go in here until November, i've got a bit of time up my sleeve.
Sounds like i should try a good clay breaking plant such as potatoes etc so that could be an option.

And get some organic material in there.

Thanks again.

John
Melbourne
Australia

imafan26
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Re: new bed suitable for vegetables

Stones makes a good edging. 8-10 inches is a good depth for most things, but I would plant something that might help break up the hard pan before planting tomatoes. Sun Hemp, Sunflowers or forage radishes. Sun hemp is also a cover crop that can be tilled in add organic matter. It is a legume so if it is inoculated it will fix nitrogen too. Sun hemp also deters nematodes.
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applestar
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Re: new bed suitable for vegetables

Australia! So you are in winter now? So you would be looking at late winter/early spring crops to start with before tomatoes. Would you be able to grow Fava beans? That might be an idea. Summer harvesting daikon, cabbage or broccoli.... If just covercrop/green manure then maybe alfalfa.

That sun hemp @imafan mentioned sounds like a useful one -- is it the right season for them?

You don't want to plant potatoes before tomatoes I think.
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bulldogboy
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Re: new bed suitable for vegetables

Yes, mid winter so days about 14-15 celsius (from memory that's probably mid 50's). Sun hemp, i have never heard of! But will probably try a legume. Yeah good point about the potatoes as they're in that same family.

Thanks USA.

jd

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applestar
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Re: new bed suitable for vegetables

Yep. If you like/(not Mediterranean descent and have physical intolerance to) Fava/Broadbeans, they would be a good choice because they grow stronger than peas -- try to pick a variety that grows tall (I grew a 5-6 footer once -- can't remember the name of the variety at the moment....).

Tall vining peas would be good, too. I don't know what you would have, but I'm talking about ones that grow to the top of 5-6 ft tall trellis -- I grow Tall Telephone/Alderman shelling peas and Sugar Snap, Sugar Daddy, and Super Sugarsnap which are all (I think called) "mange tout" type.
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