Allotment Week, Part Three - Green Manures and Ground Covers

I've dabbled a little with green manures before - mostly scattering phacelia seeds here and there at the last minute of the growing season and then cursing them when they finally appear the following spring right where I want to be planting stuff, and I can't bear to get rid of the lovely flowers before the bees have made the most of them... But last autumn I made my first serious attempt at using green manure properly.

The idea, in case you're not familiar, is that rather than leaving soil bare over winter (or at any time), you sow a cover crop of some sort. This crowds out weeds, keeps the fungal organisms in the soil happy, and protects the soil against leaching, erosion and so on - and when you're ready to plant crops again you dig in the vegetation to add organic matter to the soil. Now that I've seen our plot flood, I can see how important it can be to have roots in the ground, keeping the soil together and preserving its structure in case of extreme weather. The problem I typically have, though, is that I clear my beds too late to sow anything, or, as with the phacelia, poor planning means I want to plant right where a cover crop is doing its thing. I've also always been a bit wary about adding to my weed problem by experimenting with certain green manures which are reportedly not-so-easy to kill off when you're done with them! But after a lot of reading, I've identified a few green manures that I think suit my way of working:

Field beans, often grown for livestock feed and much-resembling a branching broad bean, are winter-hardy and germinate right up to November, so I can get away with sowing them really late in the season. And being in the bean family, their roots fix nitrogen in the soil.

Phacelia needs sowing by September latest, so I'm gonna have to try harder to clear some space for it late summer (maybe after the broad beans...?) but I think it's well worth persisting with for the lovely bee-friendly flowers it produces around May - if I can manage to leave it that long. It'd be ideal for whatever bed I'm going to grow squashes on, since they don't get planted out until May or June.

Mustard is a quick grower which is killed off by frost and can be left where it dies to decompose and mulch the soil. It's not quite the same as having something growing over winter, but I'm interested in giving it a try this year and seeing how it works out. Mustard is said to help keep soil pests under control too, so it might be good to grow this before potatoes.

White clover is hardy and long-lasting, and can be used as a 'living mulch' around perennial or widely-spaced plants. It keeps weeds down and has bee-attracting flowers in the summer, AND it fixes nitrogen. I'm going to start introducing this all over the place: we have already sown it over what is to be our squash bed (too late to sow phacelia here now for flowers by May) and I will start to scatter it round the edges of the perennial bed, letting it spread naturally. If it's growing where I want to plant, I'll simply pull it up to clear a space.

Buckwheat is a quick-growing summer green manure and to be honest, I'm not sure if I'm really going to fit it in anywhere, but like phacelia it has wonderful flowers, loved by insects, and it seems easy to deal with, so I wanted to give it a try and bought some seed anyway...

Back to 'allotment week', and our third big task was to clear last year's green manures and sow a new one. After our potatoes were harvested early last October we sowed field beans in their place, and they've grown pretty well through the mild winter, reaching a height of nine inches or so. But plans have changed since last autumn and I wanted to get some clover started here, so it was time for them to go.

Switching to no-dig gardening means we won't be able to dig our green manures into the soil, but instead we can cut down the growth and either use it as a mulch and let it decompose naturally on the surface, or add it to our compost heap. Leaving the roots in the soil means they'll add loads of nitrogen. Just look at the nitrogen-filled root nodules on this field bean stump I pulled up by mistake!

I cut the beans down at the soil surface, trying to get every shoot to reduce the chance of regrowth. I'm sure some of my allotment neighbours must have thought they were up-and-coming broad beans I was cutting down! The greens made a nice leafy layer on the compost heap.

I hand-weeded the whole bed after this - the beans don't keep weeds down as well as some other green manures are supposed to and there were quite a lot of young dandelions, docks and pineapple weed around. Then I raked and watered in some white clover seed over the whole bed. Hopefully it will have a good chance to get established as a living mulch before I plant the squashes out.

Mulching round plants helps to keep weeds down, reduce evaporation, and absorb excess rainfall in wet periods. A living mulch has all these benefits and more! It can attract and provide shelter for beneficial insects, it doesn't need replacing so often, and it has even been shown to decrease pest attacks in some vegetable plants. I'm really looking forward to seeing how this works out! Earlier this week I also read this interesting post by Alison of Backyard Larder, which talks about using edible plants such as wild strawberries and lambs lettuce as living mulches - something I am going to have to give some thought to now! I'm certain claytonia, one of my favourite home-grown salad leaves, would make a pretty great groundcover too, but judging by the way it gets everywhere in the garden I think it'd be a bit risky on the plot!

We did sow a spot of phacelia last year too, scattering it in odd patches where I pulled up individual squash plants. You can see what remains as a clump in the third bed in the picture at the bottom. I'd really like this to flower before I want to sow my root veg there... I don't think it's going to happen, but I'll wait and see, and if all else fails maybe I'll scatter a few seeds out of the way for the bees (and me!) to enjoy the flowers later in the summer!

So that's it for allotment week. We didn't get our potatoes in like we wanted to - no big deal as it's early yet - but we really did get a good headstart on the season, and did a lot of those little jobs that usually get pushed to the bottom of the list. If you follow this blog I'm sure you'll agree it's probably never looked this neat and tidy! Now, bring on some warmer temperatures and let's get some crops out there!