Posted: 01/01/2015 at 06:51
I suspect that the poor show over the past two years may have different causes. The season before last was very slow - cold temperatures and low light levels. Many veg really struggled that year.
As for 2014 - have you managed to get any organic matter into the soil over the past few years? I would try digging in plenty of good home-made compost and/or well-rotted farmyard manure to improve the structure and all-round fertility. The heavy rains of the previous autumn may have washed nutrients out of the ground, particularly as your patch is free draining and on a slope. I'd also incorporate Fish, Blood and Bone when preparing for planting this spring.
Also, have you been able to water - onions need quite a bit of water while they're growing in order to swell the 'bulb' and we had a very dry summer last year.
Hope that's helpful and good luck with this year's crop