Green Manure

 I wrote a post about green manure just under three years ago so you might want to refer to that first. In numerous other posts, I have described how I cover soil with black plastic over the winter to suppress weeds and deter cats from treating my kitchen garden as their own personal toilet. The advantage of black plastic is that it is quick and easy to apply such that the soil can be covered immediately after a crop has been harvested. In the spring, the black plastic can help warm the soil prior to sowing seed or planting out. Since the black plastic sheeting is reusable, it comes at zero cost after the initial outlay. On the downside, it adds nothing to the soil and can harbour slugs/snails - though these are easy to collect and dispose of as and when the plastic is lifted for the growing season.

From a soil health perspective, green manure (especially, the root system of green manure crops) adds and/or retains nutrients, improves the soil structure, increases soil carbon content and provides a sustainable biome for beneficial micro-organisms.

Photo 1: Green Manure Seeds

I bought my green manure seeds from SOWSEEDS.  Their website has lots of information on selecting the right green manure as well as sowing and digging-in guides. Green manure, depending on the plant chosen, can be sown from March to November in the UK. My requirement is for late summer and autumn sowing after harvest is gathered in - so I plumped for birdsfoot trefoil (Mar - August), forage pea (Sept - Nov), forage or field bean (Sept - Nov) and forage rye (Aug - Nov).

In what had been the brassicas bed*, I chose a September sowing of forage rye (Photo 2, Swiss chard (foreground) and celeriac (background)). The bare patch has just been cleared and freshly sown with more forage rye. [*due to a whitefly problem, I have stopped growing overwintering brassicas such as kale, sprouting broccoli and brussels sprouts and, for the moment, grow only calabrese and summer cauliflower]

Photo 2: Forage Rye Grass

In late August, I lifted the onions and chose field beans and birdsfoot trefoil for my green manure (Photo 3). The left-hand side of the bed still had beetroot and parsnip growing. The birdsfoot trefoil exhibited poor germination (or something ate the seeds), possibly because it was a little late in the season.

Photo 3: Birdsfoot Trefoil and Field Beans (rhs) 

After harvesting the sweetcorn crop, I sowed forage peas in mid-September (Photo 4). The black plastic is covering the potato crop which I'm storing in the ground until the weather gets colder and/or wetter. In case you haven't guessed already, the black plastic is to eliminate cat deposits!

Photo 4: Forage Peas replacing Sweetcorn

Finally, the general plot (French beans, squash, courgettes) was cleared (apart from three active courgette plants) and planted with a mix of forage peas and beans. These were only sown a few days ago so nothing to show at the moment (Photo 5).

Photo 5: Forage Peas & Beans (all still underground!)

Based on this year's experience, I would definitely recommend the forage peas, beans and rye grass. They all fit my green manure window of autumn sowing. The birdsfoot trefoil was less successful, possibly because it is better suited to a spring-summer sowing regime. From my point of view, the only problem using these green manures is that it leaves the soil bare for a few weeks - much to the delight of the local cat population. I've already removed a few deposits and I will need to be vigilant for a few more weeks.