[benkt]

So,we've got our new (to us) polytunnel up and covered and today we put some 4"-6" boards down the sides to mark out the beds. I'd like to get the beds ready for growing tomatoes,  peppers and cucumbers (we have another polytunnel that's used for all the sowing and seedlings). How would you advise preparing them? We're on fairly heavy clay and its been rotavated once, before we built the tunnel, but is still pretty hard to work. What should I add to get a nice growing bed?

[Lesley Silvester]

Lots of well-rotted manure is good. Sand will also help to break it up.

[pgkevet]

It comes down to size and budget. To improve my outside growing areas I've added rotted horse dung and cow dung and large amounts of woodchip and saw dust from processing for the woodburner and from pruning hedges etc.
For my large greenhouse I took the easy way and dumped several 125L bags of B&Q compost for it's beds ontop of  a base layer of finely seived heavier stuff. the spoil heap from digging out the dwarf walls of the greenhouse were put through a meld wesh seive i made that fitted the loader bucket.. heavy work at the time. then it all gets raked and mixed in over the years.

[Fleecewife]

Clay can benefit from added sharp grit or small gravel.  You can buy it by the lorry load for not very much.  It sounds as if your drainage deep beneath the beds needs to be improved - no point having the beds themselves draining only for the water to come up against a solid clay layer so it has nowhere to go.  If you have time and labour available, dig out a good spit deep, add a whole lot of gravel (to give about a 1:1 mix), and dig it in to the deep layer.  Add more gravel as you return the clay soil back into the bed, and mix it in thoroughly.  Then add your fertile top soil, with manure, compost, grit, seaweed meal and so on to the top layer.  Depending on the root depth of your proposed plantings, you may want to include manure into the middle layer too.  As it all settles over the next couple of years, you can add mulch onto the top, as usual, and the surface level will not go down.
It sounds like a load of work but it's worth it as your beds will last a long time.