How deep does a raised bed need to be?

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How deep does a raised bed need to be?
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Hannah

Joined: 24 Feb 2005
Posts: 277
Location: Pembrokeshire

Posted: Fri Jan 04, 08 2:33 pm Post subject: How deep does a raised bed need to be?

I have got two areas which I was hoping to use as raised beds for growing veggies. However they are on a concrete base and the sides are two concrete blocks high (about 1.5ft high). If I filled these with soil etc would these be deep enough to grow veggies in? Or would it only be okay for some and not all, and if not all, which veggies wouldn't it be suitable for?

Many thanks and Happy New Year to you all!

Hannah

judith

Joined: 16 Dec 2004
Posts: 22789
Location: Montgomeryshire

Posted: Fri Jan 04, 08 2:47 pm Post subject:

1.5 feet high should be OK for most veggies unless you are wanting to grow prize-winning parsnips or summat like that.
I'm assuming there are good drain holes at the bottom of the blocks?

ETA some of the larger brassicas might struggle to get their roots down as far as they want, but if you heel them in well, they should survive.

Last edited by judith on Fri Jan 04, 08 2:50 pm; edited 1 time in total

Behemoth

Joined: 01 Dec 2004
Posts: 19023
Location: Leeds

Posted: Fri Jan 04, 08 2:49 pm Post subject:
But filled with good moisture rententive material....

dougal

Joined: 15 Jan 2005
Posts: 7184
Location: South Kent

Posted: Fri Jan 04, 08 2:51 pm Post subject:

Different crops need different soil depths.
Most salad stuff doesn't need much.
Errr, root veg generally want more...

Check books (and links) for growing fruit, herbs and veg in containers - 'cos it sounds like you have a big (but 18" deep) container...

I must mention that I don't know (maybe others will know) what the effect on soil pH (acidity/alkalinity) of loads of concrete might be. Or what other problems (drainage obviously, frequent watering less obviously) may also need consideration...

Slim

Joined: 05 Mar 2006
Posts: 6612
Location: New England (In the US of A)

Posted: Fri Jan 04, 08 3:21 pm Post subject:

If the concrete effects the pH it'll be to raise it, though I honestly don't know if it will have any effect except on the soil directly touching it, and probably not to a detrimentally high pH anyway...

If the soil you put in is rich enough, and you make sure that it stays moist enough (this is where I think the trouble could start) than I doubt you'll have too much of a problem. Most crops only need so much soil depth if they have what they need nearby, and if you think about it, how many carrots, beets, turnips, etc have you seen that are over 18inches long? Probably couldn't handle a daikon....

Probably best to give a really thick mulch on top to be on the safe side.

chez

Joined: 13 Aug 2006
Posts: 35935
Location: The Hive of the Uberbee, Quantock Hills, Somerset

Posted: Fri Jan 04, 08 4:05 pm Post subject:
Have a look at the Square Foot Gardening chap's website: https://www.squarefootgardening.com/ He talks about a 'special soil mix' for raised beds that he claims is the business and talks about soil depth etc.. I'm sure you don't have to follow it to the letter, but it's an interesting idea. I bought the book - having read it though, it's pretty much summed up on the website.

Slim

Joined: 05 Mar 2006
Posts: 6612
Location: New England (In the US of A)

Posted: Fri Jan 04, 08 4:19 pm Post subject:
I'm curious as to what goes into "Mel's Mix". I'd assume a lot of peat, and fairly soluble nutrients? Probably be smashing for the first year but need a good dose of fertility every following year. Any garden like this will I suppose, but I'd rather mine came from good compost and manure. Less likely to get acidic like peat would, as well!

chez

Joined: 13 Aug 2006
Posts: 35935
Location: The Hive of the Uberbee, Quantock Hills, Somerset

Posted: Fri Jan 04, 08 4:35 pm Post subject:
It's 1/3 blended compost, 1/3 peat moss, and 1/3 vermiculite. I am not happy about the peat moss content. And it seems weird to completely dispense with the original soil, which is what he advises. We are on heavy clay, so compost compost compost is the way forward for us I think. One the things on my list for the next few weeks is to score some horse-muck and put in our new beds.

dougal

Joined: 15 Jan 2005
Posts: 7184
Location: South Kent

Posted: Fri Jan 04, 08 4:40 pm Post subject:

Chez wrote:

We are on heavy clay, so compost compost compost is the way forward for us I think.

Try adding some bonfire ash...

tahir

Joined: 28 Oct 2004
Posts: 45669
Location: Essex

Posted: Fri Jan 04, 08 4:40 pm Post subject:
Both of our houses have been on really heavy clay, at both by year 2 the soil was (with the addition of lots of organic matter) unrecognisable from the claggy unworkable mess we started with. It's gutting that we're going to lose all our existing veg plots when we rebuild, so shall have to attack our 96% clay soil (tested for when we were thinking about rammed earth) again

Northern_Lad

Joined: 13 Dec 2004
Posts: 14210
Location: Somewhere

Posted: Fri Jan 04, 08 4:46 pm Post subject:

tahir wrote:

It's gutting that we're going to lose all our existing veg plots when we rebuild, so shall have to attack our 96% clay soil (tested for when we were thinking about rammed earth) again

Well take the time while the new plans are, erm, at the planning stage, to get some pigs in to where you're going to have the new beds. I'm sure you're only not supposed to eat them; don't think there's anything against raising them...

Slim

Joined: 05 Mar 2006
Posts: 6612
Location: New England (In the US of A)

Posted: Fri Jan 04, 08 4:52 pm Post subject:
96% clay? Time to start firing pots and trading them for food!

judith

Joined: 16 Dec 2004
Posts: 22789
Location: Montgomeryshire

Posted: Fri Jan 04, 08 4:54 pm Post subject:

Northern_Lad wrote:

It might take a bit longer, but a good bunch of chooks would happily deforest and fertilise a prospective veg patch.

tahir

Joined: 28 Oct 2004
Posts: 45669
Location: Essex

Posted: Fri Jan 04, 08 4:55 pm Post subject:

judith wrote:

It might take a bit longer, but a good bunch of chooks would happily deforest and fertilise a prospective veg patch.

Would they?

judith

Joined: 16 Dec 2004
Posts: 22789
Location: Montgomeryshire

Posted: Fri Jan 04, 08 4:55 pm Post subject:

Oh yes!

ETA:
They wouldn't get the roots out or turn the ground like pigs, but they can scratch up turf pretty well - and they'll eat the bugs. Certainly with the numbers you are envisaging, I reckon you could have some sort of tractor arrangement - every time you move the tractor you could cover the ground to prevent regrowth.
Might be a bit fanciful, but I reckon it would work.

Last edited by judith on Fri Jan 04, 08 5:04 pm; edited 2 times in total

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