KEF, very few things in a garden - vegie or otherwise - like permanently wet roots. About the only veg I can think of - that I've grown anyway - that likes things damp-ish is celeriac. Rocket needs regular watering, too, or it will bolt in warm weather, though the soil shouldn't be permanently damp.
I seem to remember reading a recent article by Mark Diacono in one of the monthly magazines where he said that when he was involved with River Cottage, they tried never to water anything once it was in the ground.
I thought at the time that this did not seem practical, but does lend strength to the argument that we can all overdo the watering occasionally.
I've never had this problem but if the roots are not swelling, the plants may be under stress - drought/cold spell etc.
In dry conditions, water every 2 weeks.
I have just read your post and I am so interested to see you had problems with Bolthardy Beretroot last year too.
Such a disappointment. In fairness, I planted other varieties too, all in my polytunnel, and they simply didn't form roots. Loads of leaves though. I wondered if it was a soil problem. I treated them the same way as the previous year when the crop turned out well.
An excess of nitrogen - either in the soil or added later - is a common cause of leaf development at the expense of the root. Don't overcrowd them, thin out the multiple seedlings that emerge, give them plenty of sun, water very sparingly, and they should pretty much grow themselves.
A few years ago I left a tray of 3" tall beetroot seedlings, sown in modules, laying on an unused part of a veg bed for a few weeks as there was no room for them. A few weeks later I found they had rooted into the soil below and they went on to produce usable roots. I don't know if that tells us anything other than neglect isn't necessarily a bad thing!
Most plants will grow if there's any opportunity at all
i have real problems with leaf miners on my beets. Everyone seems to say that you need to try and pick off the larvae / mined leaves but that the roots themselves shouldn't really be affected. I do find though that my plants get so affected that it takes much longer for roots to swell. any tips? I'd like to try them again this yr.