Green Manures: Spring sowing update

Russ joins us for his final posting on his green manure trial.  After his autumn trialsuccess, here he gives us his verdict on 3 spring sown green manures.

In autumn 2019 I decided to test out the germination and effectiveness of green manures – something I was really interested in (in theory!) but somehow never got around to doing.  I sowed some overwintering crops and reported back (Green Manures: A member’s trial – an update).  Now I’m back with my latest update on spring sown trial.  In late March I made some sowings of phacelia – also known as tansy – (for the insects), buckwheat (good for poor soils) and red clover (nitrogen fixing legume).

This time all the seeds germinated for all the choices, but again with widely varying final results.  The pictures above were taken in March, May and June.  All the plants got off to a grand start and even in May it was too close to call who might be first past the post.  However, by late May it was clear who the winner was: phacelia.  Buckwheat was a close second and clover brings up the rear.  The phacelia grew thickly and fast, outcompeting weeds and providing shelter to the soil and the much-needed root systems beloved by essential soil microorganisms. (These bacteria and fungi cover a range of functions including decomposing, ‘fixing’ nitrogen, suppressing disease and converting minerals).  I decided to let the phacelia flower for the insects – and I’m glad I did – the plants are covered with all manner of bugs and beasties plus the bristly mauve flowers on tall plants are a lovely addition to the plot.

The buckwheat is slightly less dense than the phacelia, but it has done a bang-up job of ground cover, and would potentially have added much needed organic matter to the soil had I dug it in.  But like the phacelia, I couldn’t resist letting it flower its pretty little creamy coloured flowers above heart shaped leaves.

The red clover was very disappointing.  After a strong start, it has remained patchy and entirely ineffective at soil cover.  However, the magic is going on beneath the soil where bacteria living in root nodules (on leguminous plants such as beans & peas) are able to take or ‘fix’ atmospheric nitrogen for the plant to use.  The nitrogen is then released back into the soil once the plant dies where it can be available for other non-leguminous plants.  I will see if the clover flowers, which will be another lovely addition to the plot, plus I’ll still have the benefit of its root stores of nitrogen.

Even though I’m not going to be getting any more scientific about whether my soil fertility has improved as a result of growing green manures, or which ones are more beneficial gram for gram, I’m definitely a convert to green manures.  In summary, out of the over wintering green manures, I would definitely sow mustard again, and for spring I’ll be going with phacelia and buckwheat.  Just for the ground cover/ weed suppressing alone they make for a simple, relatively cheap and rather more attractive alternative to my usual cardboard.  Plus, they have the added benefit of attracting insects and potentially increasing the soil’s fertility.  I’m sold.

Are you interested in trialling a crop organically?  Or testing out a method of growing?  Got a surprising observation to share?  BHOGG would love to hear from you.  Email us at, post below, or link into twitter to tell us.

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