[Diddy Gardener]

All was going well until I noticed this morning that some of my beetroot leaves are turning yellow... just the outside ones (so far). I'm in Scotland so it could, of course, be the weather!

[Trillium]

Beets actually like cool weather. Sounds more like some sort of chemical spray hit the leaves, maybe carried in on wind.

If it's the outside leaves of every plant, then you might want to give the beetroot a light fertilizing or manure tea watering.