Digging green manure into your vegetable plot

This winter I grew two types of green manure on one of my allotment beds that was otherwise empty. This was supposed to suppress weeds and improve soil structure ready for planting vegetables in spring. But did it work, and which green manure was best? This week it was time to dig it in and start finding out...

Reasons for growing green manure

Green manure is grown to suppress weeds and enrich the soil. I've never used it before so it was a bit of an experiment. I covered other beds that were empty over winter with compost, leaf mould or manure. The rain and the worms break these down and work them naturally into the soil.

Green manure is an alternative way of improving the soil while there are no crops growing there. 

I sowed two types in autumn: phacelia and ryegrass. They germinated and grew, occupying the bed over winter. The plan was to keep the weeds down and then dig the green manure in before it sets seed. 

Phacelia growing on the left and ryegrass on the right

As you can see they grew pretty well. They certainly prevented weeds coming through. There were very few weeds amongst the green manure, whereas in the corner where I didn't sow any (bottom right in the picture above) you can see clearly the usual weeds were present, as a close up of that area shows:

This corner was free of green manure - but full of weeds!

Last week I cut down all the green manure so that it wouldnt get a chance to set seed and potentially spread all over the place. I just pulled it up by hand or by dragging a rake across it, leaving it lying flat on the ground to dry up and weaken:

Green manure lying on the ground after being cut down

This week I went back and dug the green manure into the ground. I just turned the earth over with a spade so that the plant material became buried. I also sliced it with the spade as I went, to break it into smaller pieces:

Slicing the green manure with a spade whilst digging it in

Once I'd finished, the earth covered most of the green manure, apart from a few strands:

Green manure buried and left to decompose

Now covered by earth it should break down fairly quickly and add nutrients to the soil. When digging, it certainly felt to me like the earth was easier to work than usual for the time of year, suggesting that the network of roots grown by the green manure crops had helped improve the soil structure.

This could be by using some of the moisture from what is a very damp site in winter. Other plots on the site have been flooded during winter storms. My plot has escaped but the water table is always high and the soil boggy. It seemed less boggy than usual.

At the same time the surface moisture appears to have been retained under cover of the green foliage, making it soft and easy to dig without being heavy.

Which green manure was best?

The phacelia was significantly softer, and therefore easier to cut down and dig in. The ryegrass developed quite tough stalks which were more difficult, so I think I'll use the phacelia in future.

All of this is completely anecdotal but I will certainly be trying it again next year. Using green manure only cost a few pounds for two packets of seed, and cutting it down and digging it in was less work than carrying and spreading numerous bags or barrow loads of compost or manure, and has also reduced the amount of weeding I need to do. 

Happy growing,

Paul

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