Phew! None of you got it so I shall be able to keep this magnificent and extremely expensive prize to myself.
CmdrK was closest. The hoop is filled with gravel. I'm going to put a round grobag on top of the gravel and then grow runner beans in it. I have another hoop on the other side of the growhouse for tomatoes. And the gravel will help keep the slugs away!
This is my theory anyway. I've invented this method, it is copyright to moi
so clear off all you sneaky gardening tip thieves.
I was going to heave bags of compost around today but I've woken up with a terrible cold so that will have to wait - but I will let you know if it works.