[ConfusedGardener]

Thanks snowdrops. I will do as you suggest.

Then by the same token, should I also rotate tomato beds every year?

[snowdrops]

Most definitely & not to where the potatoes have been. Have a look at the info on crop rotations in articles & advice at the very top of the page., lots of good info from John the site owner. 

[ConfusedGardener]

I had looked before, but my memory is like a sieve... it'll sink in eventually

[snowdrops]

Don't worry it's a steep learning curve, I keep a little chart in my allotment planning folder.