2019/20 Green Manure Trial – Setup and Sowing

Yes, I’m starting another growing trial! This one came about as a result of a moment of Twitter-based Serendipity that resulted in the good people of SowSeeds.co.uk – who also run the rather excellent green manure seed sales and information site GreenManure.co.uk – sending me four varieties of autumn-sown green manure crops to try out.

I’ve set up a trial area down on Plot #59 – four 1m x 1m sections – as you’ll see below, and I’ll also be running a larger-scale trial at work, on the allotment beds at Ordsall Hall and Gardens, with the full connivance of our Head Gardener, Jo Green. The gardens at Ordsall Gall are 100% organic, so green manure is right up our horticultural street.

I’ll be assessing the four trial crops – caliente mustard, field beans, forage (Hungarian grazing) rye and Italian ryegrass – on criteria such as speed of germination, rate of growth, degree of ground coverage, weed suppression, maximum growth extent and ease of incorporation. For the allotment trial, I’ll be adding a slight twist: because I prefer to use no-dig methods wherever possible, I’ll be seeing how easy it is to use minimal incorporation methods – shearing the tops off the plants and gently forking over the root area – and then assessing what sort of re-growth occurs, and what sort of impact it might have on the follow-on crop of beetroot that I plan to grow in the beds next year. And of course, I’ll be trying to assess what sort of boost, or not, the four green manure crops give the beetroot crop as well.

Here’s the setup method I employed for the allotment trial area, in case you’re interested in running a trial of your own:

1. Clear the Ground

It’s important to get rid of any established weeds that might choke the green manure seedlings before they get going. Inevitably some weeds will end up competing with the green manures, because disturbing the soil by raking it to a fine tilth will expose dormant weed seeds and give them a chance to germinate as well. Although annual species can be incorporated along with the green manure crop, so it’s really the perennials you have to be absolutely sure to remove. But anyhow, why give them a head start?

2. Mark Out the Trial Sections

You could use string lines, or tapes, or planks to mark out the general sowing area. But I wanted something a little longer-lasting and more easily visible and so I opted for canes.

First, I measured and laid them out, then used cut-off ends of old canes as pegs to hold them in place:

A plastic bottle on top of the pegs holds the cane down whilst providing a handy support for the fleece tent (see below) and a bit of added visibility when the fleece comes off.

Et voila, the trial beds ready for sowing:

3. Sow and Cover

I sowed the seed at the rate recommended on the packets, weighing the measures out at home and bringing the portions of seed along in separate seed envelopes:

  • Caliente Mustard: 1g per m2
  • Field Beans: 20g per m2
  • Forage Rye: 17g per m2
  • Italian Ryegrass: 10g per m2

I sowed as regularly as I could, either scattering, then lightly raking, then tamping down with the back of a rake and watering in, or poking them an inch or so into the soil in the case of the field beans. (I have to confess that I might have over-sown the mustard because my kitchen scale had difficulty registering a single gram without jumping between 0 and 2, but I guessed somewhere in the middle. The seeds are feather-light, so you will end up with a surprising number in that one gram’s worth.)

Finally, I covered the area with a tent of horticultural fleece; partly to provide a bit of extra warmth an insulation to aid germination, but mostly because I knew that if I didn’t then the local pigeons would eat both lots of grass seed the second I turned my back.

And now, we wait. As always, further updates will follow.

Edit: October 3rd A quick check today and the mustard and both types of rye have begun to germinate. No sign of the field beans yet…

In the meantime, how about you? Do you regularly grow green manure as a cover-crop or soil conditioner? Which varieties do you use, and what sort of results have you had? Please do let me know, via the comments.

And if you’re a complete novice but would like to know more about green manure crops, then do check out the information pages at GreenManure.co.uk, they’re a great place to start.

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