[Dans]

When we moved we inherited a very large polytunnel. The previous people had weed proof fabric down and the clay soil underneath it look absolutely baked when we pulled the fabric back. Rock solid and full of cracks like you see in a parched desert.

We decided to go for no dig and piled a mix of well rotted compost and soil improver on top. We did 4 beds. Some we just poured straight on, some we cracked the surface with a fork and some we thoroughly soaked first, some were a combination.

In all of them some veg has pushed through into the clay layer below, but a lot of plants just put thier roots horizontally along the length of the beds. In all of you push back the soil surface you can feel the clay layer just as hard as it was.

That very long explanation leads to my question. Should we rotavate?  Would a rotovator even penetrate that? It was very hard with the fork you break the surface?

I like the no dig approach but the ground underneath my beds seems like concrete. Would I be better just raising the beds even higher?

Dans

[Fleecewife]

You need to break up the hard pan Dans, or no water will drain through.  Very hard work but I would suggest a pinch bar (long crow bar thing sold for fence hole prep.)  You kind of throw it at the ground repeatedly (vertically at first then horizontally when you hate it too much to do any more  ) then wriggle it around.   Ideally you want to break it up as much as possible then leave it exposed to winter frosts - frost is better at breaking up clay than anything.   But is this the tunnel you have your geese in?  That adds a problem.
Once you get to the point where the whole surface is broken to about 6" deep, then buy a load of sharp gravel - about 2 mm - and dig in as deep as you can. Sharp sand will help too. This will reduce compaction of the clay and allow the water to drain through and the earthworms to pop up.  Once worms can get through they will work to draw compost down into the clay, which will gradually make you a good loamy soil.  Clay soils are really fertile, much better than sandy, but do take a few years to make usable.
I would keep a rotavator well away as it simply moves the hard pan lower, if you can get it to do anything more than skim over the surface.

[clydesdaleclopper]

In that situation I would recommend using a broadfork. It breaks up the hard pan as you work at successively deeper depths without turning over the soil and losing the benefits of no dig.

[Anke]

Unless your polytunnel is really high a pinchbar (ours is about 6ft long) is not very useful - you are in danger of pushing it through the polythene above your head by accident... use a mattock or pick axe, just be careful when swinging.... we did that in ours. Then built raised beds, about 25 to 30cm high.

We found this year (10 years of use) though that the soil - despite regular dressings with manure - seems quite exhausted, as the beans/peas and beetroot all were terrible. Now planning on taking out a lot of soil, refilling with fresh topsoil, plus manure, seaweed and rock dust. One thing that probably contributed  was that I left it going dry in winter usually.... not good, but as it's our hay storage unit as well it was difficult to keep wet.

I am quite sceptical wrt no-dig and heavy clay soil...

[Dans]

Thanks guys.

It's not the one the geese are in, they are in one of our 'small' tunnels. We have the big one and then two smaller ones.

Our polytunnel is very high, the support beams that go across are over 6 foot and then there is a lot of room above those. I could see myself throwing the pinch bar and puncturing the sides if it is the thing I am thinking of though. It was very heavy!

I think we had one of those pinch bars in the old house but forgot it there. The broad fork looks very good, I'll see if I can tempt the OH to get one. I'd just be a bit nervous about how you get started with the broadfork, the ground seems so hard.

The water does currently drain but I think that is because the cracks in the hardpan are so large! The water just pours into them currently.

What do you mean you left the tunnel going dry @Anke ? My OH keeps asking if we should water the tunnel at the moment but the plants seem fine and I worry about the frosts so we haven't been. Is that bad? We don't store anything else in there really.

Dans

[clydesdaleclopper]

When you start with the broadfork you just go in a little way at a time. As you continue to do it you work progressively deeper.

[Dans]

Any recommendations on a broad fork? Tuesday OH has given me the green light 

I've found this one:

 http://www.blackberrylane.co.uk/broadfork.html

But most seem to be stateside.

Dans

[Fleecewife]

It does look brilliant, but...ouch, it had better be at that price 

[Anke]

What do you mean you left the tunnel going dry @Anke ? My OH keeps asking if we should water the tunnel at the moment but the plants seem fine and I worry about the frosts so we haven't been. Is that bad? We don't store anything else in there really.

Dans

Well our polytunnel doesn't have much during the winter, so I don't normally water and the soil goes dry. Not in a hard layer, but just really hard lumps of clay...

I like the broadfork design, just no way I would pay that amount of money for it... sorry.

[Dans]

Well the OH reworked at the broadfork and hadn't seen the price  I have to admit I had been surprised at his green light.

We sat and talked and decided that we are probably aright digging through the soil structure in the polytunnel as it does seem quite dead, no worms in sight.  So we will attack it with a fork in the cracks and sledge hammer.

I made a start by shovelling away the soil improver we had put down and grown in last year. The clay was pretty much as it had been when we made the beds. As I moved the soil though a family of mice came running out from one of the cracks in the clay! Will see how it goes and report back.

Dans

[Anke]

More likely voles rather than mice? That's what we have in the p/tunnel, and sadly the cat is not really making a difference at the moment in there. although I find dead voles round the place regularly...

[Dans]

Could have been voles. I was quite distracted screaming and dropping my spade lol

Dans

[farmers wife]

Personally I would have dug as much out as possible and bought in some quality top soil and then layered with compost or mulch.  you cant change structure of soils you have to work with them.  Other options is to  build raised beds which we did.  Growing in poly you shouldn't have too much with long root structures.