This year I’ve been trialling two species of clover on behalf of the folks at Garden Organic. The idea of the trial is to assess the usefulness as a green manure of a relatively new (to the UK) species, Trifolium resupinatum (Persian clover) as opposed to the more widely-known and commonly used Trifolium incarnatum (crimson clover).
Back in August I posted a few pics that showed both species growing well, albeit with a clear lead for the crimson clover over the less vigorous Persian. The other day, I took a couple more pics that show what’s happened to both in the warm Autumn we’ve had here in Manchester:
As you can see, the crimson clover is still doing well. The plants are thick and healthy and those flowers have been magnets to the local bumble and honey bee populations for a couple of months, and show no signs of slowing down or dying back.
By contrast, the Persian clover isn’t looking anywhere near as healthy. The plants are much thinner on the ground, and the patch that I sowed has been colonised by Poa annua (meadow grass) and Ranunculus repens (creeping buttercup) – a perennial problem throughout our plot – as well as a few spikes of crimson clover from the patch next door.
I realise that this is just one trial, on one plot, in one part of the country, so there are an awful lot of localised soil- and weather-condition variables in play. Obviously I’d need to see the results of the Garden Organic survey as a whole to draw any firm conclusions. But based on the results of my own small experiment, I’d be reluctant to choose Persian over crimson (or white) clover as a green manure crop in future.
Although having said that, green manure is meant to be dug in when it reaches maximum foliage and before it flowers and sets seed, rather than left for a full year as requested here; Garden Organic are also interested in how well the dead plant matter rots down into the soil. Then again though, those earlier pictures show that crimson clover put on a lot more growth a lot quicker, creating a lot more organic matter to be dig back into the soil, or cut down and used as a surface mulch.
I’ll continue the trial over the winter and see what happens to the two patches once the clover does die down, but I rather suspect that the Persian section will be overcome with weeds to the point where it will be difficult to tell what’s happening to the decomposing stems. We’ll see what happens in due course.