[caz739]

Hello. Several of us (24) are trying to get some raised beds allotments on some disused tennis courts where I live. We are applying for a grant, but I wanted to know what is the minimum depth that most veg will grow happily / successfully. I know that things like potatoes carrots and parsnips need deeper beds, but for other veg, how deep do we need to be? We cannot take up the surface of the tennis courts,so have to put planters on top.
Any help would be appreciated 

[fatcat1955]

6ins should be ok but if the courts are hard courts ie asphalt you may have a problem with drainage. If so make the beds 8ins fill the bottom 2ins with gravel and drill some holes in the bottom 2ins of the sides.

[Yorkie]

Personally I don't think that 6" is deep enough to give a decent root anchorage - I'd look for 10-12".  I agree about the drainage comment / suggestion

[caz739]

Just wondering - would sand be ok in the bottom for drainage? We are by the beach and have loads to spare

[DD.]

In most seaside resorts I've been to, it's illegal to remove sand from the beach, so you'd better be careful. (Perhaps you could put your rough location in your profile).

I'm not a raised bed person, but I'd agree 6" depth is not enough, unless you stick to shallow rooted salad crops.

[Tigerhair]

It depends what crops you are growing, but I agree that you need way more than 6".  You definitely need a base layer of drainage material - try local builders to see if they have any broken up hardcore and try the local recycling centre for the same.  Also, try garden centres, as those polysyrene (spelling?) plant holders broken up are brilliant - they may have a load you could use?  Or some.... I think I'd go for narrow (2m max) long planters - as deep as you can make them with at least a foot of soil or you'll grow very little.  There is no point doing half a job, do it properly and you may just get there.  It'll be filling them with soil that will be expensive!!!  It may be cheaper to lift the court surfaces and dig!!!  Good luck!

[savbo]

2 scaffold boards high would be a good working depth. Alternatively you can follow the model used elsewhere around the country and use tonne builders bags half filled with topsoil - easy to move if you ever have to and little effect on the surface underneath...

These sort of temporary/'meanwhile' allotments are going to be seen more and more...

[shokkyy]

I have raised beds that are just 6" deep. They sit on top of an area of old concrete, which is cracked and breaking up, so the drainage works fine.

But in 6" depth, last year I grew strawberries, tomatoes, courgettes, onions, shallots, garlic, mini carrots, celery, french beans, mange tout. They all did extremely well and gave me a very good crop. That depth will place some restrictions on you, because you won't be able to grow any root crops that need more depth (parsnips, carrots), and you obviously won't be able to grow anything perennial other than a small plant like strawberries. You also have to be a bit creative about any plant supports, because you can't just stick a cane in the ground and expect it to stand up on its own in that depth. But other than that, I've been growing just about anything in them.

One option might be to do a few separate raised beds rather than one big one. You could do some deeper, for the deep root crops, and some at 6" for the other crops. That would save you some money, if you're paying for top soil, for example, but would allow you to grow just about anything.

[noshed]

Good advice there - got any pics?

[TerryB]

If its a community plot your after, consider including a least 1 bed at 2' 6" for wheelchair access. This will help when applying for grants. As far as filling the beds check out local ground works companies as these need to get rid of soil after installing drives etc.

[caz739]

If its a community plot your after, consider including a least 1 bed at 2' 6" for wheelchair access. This will help when applying for grants. As far as filling the beds check out local ground works companies as these need to get rid of soil after installing drives etc.

We have planned 6 sets of beds with 1.4 m+ round each bed to allow for wheelchairs. 
Thanks for the suggestion on groundworks - I will see if there are any local ones.

We will hopefully have some deeper beds each, but I was trying to guage what depth the shallowest bed needed to be, so thanks for all your replies.

[Ma and Pa Snip]

This is going to sound a bit 'off the wall' but when it comes to your solid base that seems to have been of concern to some I will use two words... Roof Gardens.

It might help your plans to find out how some of them have been designed and built. Albeit they were probably damn expensive, it could give you some ideas.

What has been said already about depth is right though, in most cases 6inches just wouldn't be suitable.
Mind you having said that how many veg plants are grown in tom bags these days.
(PS now stands by to get shot down as to how successful growing in tom bags is or isnt, but hopefully not on this thread).

Instead of just having raised beds combine some 'growing boxes' made out of old pallets, ask a few local companies if they would donate any they might care to get rid of. Even damaged ones can be used to make others good.
 By carefully removing and refixing the slats you can make them into sold side boxes. Couple of good coats of preservative inside and out, fill with soil and away you go.

Sinks or baths, often seen in skips,  there's another potential freebie if you ask nicely.

If I was in your shoes I think I would be aiming for a variety of beds made from just about anything that would hold soil in order to get your project off the ground (pun intended)  ranging from minimum 9inch (22.9 cm)  to 2ft 6inches (76cm ) height.

Good luck

[Tigerhair]

More thoughts - perhaps if it looking pretty isn't important, you could try local factories and see if they have any old tubs (the one I live near has huge ones they can't get rid of - about 4 x the size of a bath with drainage in the bottom...) or anything else you could use to contain the soil.

[fatcat1955]

Even if you could take the beach sand i would be wary due to the high salt content.

[caz739]

Unfortunately it does have to look "pretty" It is right in the centre of the town park with lots of houses overlooking it. We have already had complaints that it might look like a "shanty town, like other allotments" so we are having to design it very carefully.
If there was any other land available, we would take it, but there doesn't seem to be any land that isn't contaminated