"Janet Galpin" wrote after"david taylor" :

I grew onions for over 20years in Cheshire on loam in 2 locations.
Sunny position, pH about 6,moderate amount of manure, about 1oz/square
yard of growmore.
I had good crops and enough onions from 150 sets to last a family of 6
through to April/May from August.
I am trying to grow onions in Devon on a clay patch surrounded by
trees. I apply horse manure, pH is about 6-I dressed the vegetable
plot with lime last winter, I use growmore at the same level as that
in Cheshire.
A lot of the sets hardly grow at all and the largest onion is about 4
ounces. Some go to seed early, but much of the plot becomes shaded by
trees after the end of July.

I don't know whether it's significant but this year my onions ended up
on a patch which had had quite a bit of compost added over the winter.
They didn't like it. The soil seemed too loose and it took them a long
time to get a foothold. I resolved not to grow them on freshly composted
ground in future. I just wondered whether too much manure could have the
same effect. However, you used manure in Cheshire too, so perhaps not.

Yes, but clay soil hold on to the nutrients very well, they do not leech out
as in a normal soil so any manure of fertilizer used on a clay soil is still
there despite rain etc.
We have grown good onions , av 13 oz, on Thames silt/clay for years. No
manure, that's for the spuds, only a light sprinkle of growmore.
Onions also need Phosphorous to do well, is your soil deficient?

--
Regards
Bob
In Runnymede, 17 miles West of London