Jennifer Brodie has a theory. That the obesity problem Britain – and, indeed the world – is facing is down to our bodies craving trace minerals.

She believes that every time we harvest vegetables we deplete the soil, yet with traditional fertilisers we’re only putting back basic fertility – Nitrogen, Phosphate and Potassium, AKA NPK.

We’re missing out the minerals veg – and humans need. The veg we eat has less and less of those minerals in it, so we eat more and more to try to replace it.

It’s a seductive idea and makes sense, even if most of the people I know, including me, don’t tend to binge on vegetables.

Where I think she might have a point, though is that our soil needs minerals. Mine does, especially. When I installed my new raised beds last year (with the sterling work of Heroic Paul – thanks!) I couldn’t afford the huge amounts of topsoil they needed so I just filled them up with manure, diluted with spent soil out of containers. It must be the worst soil soup imaginable.

I do have a compost bin (two, actually, both second hand; thanks to Mike & Sue and Mark & Julia) and the worms are doing their work, but it could do with a bit more than that.

I’m going to try various different types of soil improver in different beds this year, but I thought I’d start out with the compost bins.

Remin Volcanic Rock dust is exactly that – stupendously old volcanic rock dust from Scotland – sold either as a soil improver to add as a top dressing, or as a general tonic for compost bins and wormeries.

Since worms are the chaps who actually make the trace minerals accessible to plants it seems best to put the sample bag Jennifer gave me to use where I’ve got the most wriggly friends. I’ve sprinkled the contents into my current bin, given it a stir (making a wish, obviously – stirring and wishes always go together in my book. Christmas puddings get a double wish.)

I’ll report back when it’s time to reveal the next batch of lovely compost…