[Zippy]

I am hoping this is not white rot.

Some onions have comeup with a white-grey damp rotting at the base, though these were onions that had bolted and I am hoping it is just that they have started to rot in the ground rather than having white rot.

No wilting of top growth, still green and tall though bolted.

What do others think?

[Aunt Sally]

As the top is not wilted it might just be rotten because the soil is too wet.  White rot usually happens in hot dry weather and the foliage generally wilts and turns yellow.

[Zippy]

Soil too wet - this may be the case as I have probably been over-watering in this part of the allotment (nearer the water butt!). Onions further away seem to be ok.

My first year as an allotmenteer so I am finding a lot of things I have been doing to ensure good crops have either been unecessary (like too much watering) or have actually damaged crops, like too much watering or periods of watering and then not watering which I think has caused the onions to bolt and possibly some to rot.

[Aunt Sally]

That's a lesson you've learnt then Zippy  

[Zippy]

Certainly is!  :roll:  

[DD.]

Apart from initial planting, I've not done any watering whatsoever on my plot as yet. (The time will come soon enough!).

Holding back with the watering will, in general, encourage plants to put deeper roots down to go in search of it. If it's available on the surface that's where they'll stay.