"david taylor" wrote in message ...
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.
The local weeds-red campion especially are very active and I have to work to keep them down. In spite of this the crop is very poor and only lasts my wife and I through to mid November.
Any helpful thoughts please.
Regards
David T.

I have the exact same problem. I'm on Devon clay too, and
have trees that contribute some shade at times, but that can't be the whole problem. This year some sets grew reasonably, whilst others barely grew at all, and they were side by side!
I have a feeling at least some of the trouble can be traced to the clay. Though fertile, it stays cold in spring, retarding growth, and although onions may not mind so much, carrots seem to detest it.
I am thinking of experimenting with poly sheets next spring, to warm the ground up. The other possibility is to use raised beds, or add a lot of organic matter to the soil to lighten it. Another problem I get on a variety of plants is chlorosis, which is caused by magnesium and/or iron shortages: this may be caused by an insufficiently acid soil locking up these elements. My ph is 7 or even a little over.
I would also be interested in hearing any ideas.

Andy.