West Midlands,
United Kingdom 
I have been very pleased with using yellow mustard as a green manure - germinates in a couple of days, holds the nutrients in well, reduces soil pests and adds organic matter.
Has anyone tried Yellow Sweet Clover or Phacelia? They look quite decorative but have they performed well as a green manure? I know that Sweet Yellow Clover must be cut before seeding as it is rather invasive.
I need to rejuvenate a tired allotment with rather heavy clay soil next spring.
27 Sep, 2013
Answers
We've used Phacelia and found it worked well and was popular with the pollenating insects.
27 Sep, 2013
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a neighbour has used Phacelia and says it was 'good enough'. as a Yorkshire man I suspect this meant it was good.
27 Sep, 2013