Mulching

You can use all sorts of mulches for all sorts of reasons roofy, to keep in moisture, protect in winter, to feed etc. & you can use all sorts of things like straw, plastic, manure, gravel, leafmould, homemade/bought compost, slate pieces, bark chips etc. Like grindle I use gravel in some of my big pots as it helps stop weeds & pests a little bit as well. I've never used mulch on my tomatoes because I tend to grow them in grow bags with grow rings in them so there's not much surface compost showing or in big pots which like you I end up watering a lot. You just have to be sure to wet the compost well before you apply the mulch & make sure that when you water again it can soak through somehow, you could use circles of black plastic cut from compost bags if you punched lots of holes in & pinned them down, or gravel would probably be the easiest option.

I like the idea of the bark, Bess (and SueA). I was tempted by grindle's idea of pebbles, but I suspect it would be slightly more awkward scraping them all off in Winter when I empty/clean the pots.

I shall hie me to Wilko's on the weekend.

Presumably I should leave SOME bare soil near the plant so that I can still water them ? (otherwise presumably the bark would prevent water getting IN, as well as water escaping by evaporation ? )