Overwintering Green Manure

I have used a number of Green Manure strategies this Winter as part of my soil fertility building program. In fact I think that I have shifted from growing food to growing soil as my primary activity. Using a Green Manure provides a number of benefits for me, which I’ll describe below. Please note that this is an explanation of some of the things that I have done this Winter, and not an attempt to teach people how a green manure should be used.

Green Manure Benefits

There are some really good sources of information about the benefits of growing a green manure crop. This covercrop pdf lists an amazing number of crops, combinations, and advice. However I had some particular benefits in mind.

Mycorrhizal Fungi

When looking at the factors that help maintain a healthy mycorrhizal population, keeping actively growing roots in the soil is possibly the most important factor. If I simply harvest a crop, spread compost, and then leave that bed alone, I have no roots for the fungi to colonise.

Microbial Activity

Microbial activity is stimulated by the secretion of sugars by plant roots. This is one of the primary drivers of the soilfoodweb. Although this is likely to be reduced in the Winter, any time that the plant is actively growing, I hope that my soil is benefiting from this.

Soil Protection

Bare soil can be harmed by heavy rain, creating capping. A dense green manure crop can reduce this.

Biomass

Growing a green manure crop creates more biomass, rather than just shifting materials in from outside.

Nitrogen Lifting

A green manure crop sown in late Summer or Autumn can help to reduce the loss of Nitrogen through ‘leaching’. it does that by using the Nitrogen to build itself, effectively acting as a storage vessel. When the green manure is killed off, microbes make that Nitrogen available for a following crop.

My Green Manure Strategies

 

green manure mixture 1

Multi species green manure mix

What I wanted to achieve was to use a variety of different Green Manure strategies to see how they performed. Whilst using green manure has a number of benefits, I also wanted to try some hardy plants that would give me a yield of food, as well as build soil fertility. The picture above is an example of that.

Edible Lupin and Garlic

Barely visible at the bottom right of the picture above is the top of some Edible Lupins, planted out in October, inter-planted with garlic. I was given some edible lupins to grow by a friend in Portugal. I harvested some from a Spring sowing last year, but the packet suggested that they were normally sown in Autumn in Portugal. I’m not sure how hardy they are so I used them as an over wintering crop to test that out. Unfortunately the Winter has been so mild, that I still don’t know how hardy they are.

Lupin and garlic Intercrop

Lupin and garlic

The picture above shows the garlic and edible lupin intercrop. The lupins have grown so well that they are preparing to flower in FEBRUARY The picture blow shows one of those flowers forming. (Look at the colour of the soil at the bottom of the picture. I love soil)

edible lupin grown as a green manure

Flower bud of edible lupin

Some might say that this isn’t a green manure, but the combination is performing all of the functions that I wanted from a green manure. Both plants will produce plenty of biomass to compost, or return to the soil as mulch. They both provide food, and the lupin also provides bee forage. The plants have been growing all winter whenever the temperature has allowed.

Multiple Species Green Manure Mixtures

green manure mixture 1

Multi species green manure mix

Beyond the bed of Autumn sown garlic there are two beds that I have sown with multiple species green manure plants. These beds grew Onions and Garlic last year. Both of these are harvested relatively early, which allows a wider range of species to be grown. The furthest of these beds was sown with a mixture of broad beans, phacelia, crimson clover, and persian clover. All of these are winter hardy, and will need to be killed before the next crop, which are brassicas. This family should make good use of the nitrogen released by the decomposing green manure. The closer bed was sown with a similar mix of green manure plants, but with naked oats replacing the broad beans. The idea behind that was for the oats to be winter killed by the cold. That hasn’t happened, and I cannot be sure if that’s due to the mild winter, or if this species/strain of oat is fully winter hardy. Only a really cold winter will tell, and I cannot control that.

Oats in green manure

Oats in green manure

The picture above shows a close up of some of the oat plants growing amongst the phacelia. The picture below shows some of the Broad beans in the other mixture.

Green Manure mix with broad beans

Green Manure mix with broad beans

The broad beans are some of my Bunyard’s Exhibition seed. They have consistently struggled in hard winters, so I decided to use them here, not concerned about their survival. Again, the mild winter has left them relatively unscathed, and already flowering (late February). As I am also growing a Field bean (Wizard), I will need to cut the green manure beans back to avoid crossing. Whilst these mixtures have a range of functions, I have only used seeds that I had available to put them together. They are not customised for optimum benefits. For example, a mix of oats and beans may have been better at creating biomass, and Nitrogen lifting. a mix of oats and radish may have been better at opening up the soil.

intercropping field beans and onions

Field beans and onions

The picture above shows some of these beds looking South. The bed in the center has field beans in the foreground. These have overwintered, and have recently been inter planted with Onion sets, which are yet to emerge. At the far end of the bed are Autumn sown onions. These have been planted in clumps of four, spaced at 12 inch intervals. This makes weed control easier than a uniform 6 inch spacing. The picture below shows this. Although not all of the sets have emerged, most have, and some have only emerged recently.

Autumn planted onions

Onions clumped in fours at 12 inch spacing

The bed to the left is the broad bean green manure mix, although there is some overwintered salad and celery in the foreground.

The bed to the right has Autumn planted garlic and edible lupins at the far end. The near end is being planted up with more field beans. These are the same age as the plants in the central bed, but have grown better in modules with protection. using ordinary soil in my potting mix has meant that the bean roots have been colonised by Nitrogen fixing bacteria, as can be seen in the picture below.

Rhizobia

Colonisation of field bean roots by Nitrogen fixing bacteria

Hopefully this will give the plants a good start in life.

Looking Ahead

I still have plenty of work to do to design an effective green manure strategy. My recent reading has made the suggestion that soil fertility could be built just using rock dusts and green manure. I think that would be an interesting experiment to try.

 

 

 

 

13 thoughts on “Overwintering Green Manure

  1. Anni Kelsey

    Hi Deano
    I agree with your thinking on this – keeping plants growing all year round is really important to soil life and fertility. I have had field beans flowering from autumn through to now – it’s a bit uncanny to see them.
    I haven’t heard of edible lupins before so that was really interesting as well.
    Keep up the good work!
    Anni

    Reply
    1. Deano Martin Post author

      Hi Anni
      http://en.wikipedia.org/wiki/Lupin_bean
      My beans came from Portugal but you can buy them from a number of seed suppliers, and in bulk as dried beans from specialist food shops.
      I think that the trick with green manures is to decide what exactly you want from them, and then customise a mix to deliver those functions. With lots of grains to choose from, they are likely to feature more in my green manure plans in the years ahead.
      Deano

      Reply
  2. Gill

    Interesting post. I love the information you share with everybody and how you do it. I’m finally getting around to trying green manures this year (southern hemisphere) and intend to plant clovers and medics. Your use of broad beans and lupins has given me some ideas too. Thanks!

    Reply
    1. Deano Martin Post author

      Hi Gill
      If you are saving your own seed, then a green manure is a cheap alternative to loads of compost making. A really clever way of growing would be to find ways to keep following one crop immediately with another, and including plants that make a lot of carbon, but that’s a project that is a few years away at the moment.
      Wishing you well
      Deano

      Reply
      1. Gill

        Yes, that would be perfect. I battle with carbon here – Mediterranean climate (hot, dry summers) and rather poor acid soil with almost no humus. One thing that concerns me is the PT required to dig the green manures in. Clovers are manageable, but I’m not sure about lupins and other large rooted crops. At the moment I’m making compost as fast as I can and bringing chicken manure/sawdust compost and straw for mulching in a few times a year. Obviously, the ideal would be to not have to bring anything onto the property. I’ve planted comfrey and I compost weeds (and everything else) with great enjoyment. All the best.

        Reply
  3. MikeH

    Hi Deano,

    Excellent article. We use cover crops in rotation. One year we feed ourselves and the next we feed the soil since growing annuals is an extractive process. We use bush peas early in the year when the soil is still cold and chop and drop them just as they start to flower so that the nitrogen fixed from the air isn’t used to produce flowers and then peas. Into the surface debris, we seed buckwheat. We chop and drop after they flower but before they seed. Into this we plant Daikon aka tiller radish which we allow to winter till. We never leave the soil uncovered.

    We also have plots where we plant each of these crops just to harvest seed so that we can repeat the process without external imports. Saves money too. LOL

    Another very detailed cover crop resource: Managing Cover Crops Profitably

    I’m quite interested in the edible lupins that you used. Would it be possible to get some seed from you? I’ve been growing sweet varieties from GRIN-US and trying to breed a landrace selected for size, lack of bitter taste and early harvest.

    Regards,
    Mike

    Reply
    1. Deano Martin Post author

      Hi Mike
      I think that I have the green manure / cover crops book that you mention. It’s one of a great set of resources available from SARE.
      The Lupin seeds that I have are large white seeded, looking like a slightly smaller butter bean. They are sold all around the Med region. It may be that yours are already less bitter. The seeds can be bought fairly easily http://lupini.us/ . The lupins were in the polytunnel last year, and so are a bit mouldy. I’m happy to grow them on, but would be loathe to send inferior quality seed away, especially overseas. I’ll happily send you some of the seed from the stuff in the picture, which will be ready this summer.
      If I was starting out agian, I would leave more growing space to allow for a period under green manures, and perhaps use the chickens to process them.
      Nice to hear from you again
      Deano

      Reply
      1. MikeH

        Hi Deano,

        The seeds that I have are tiny although sweet. I went to the link you suggested. They ship within the Continental U.S. I don’t live there so that’s a problem. Thank you for your offer of seeds from you crop. I do appreciate it. I’ll mark my calendar to drop you a reminder note. LOL

        The soil in this video is fantastic looking – http://youtu.be/Blxe7S41q9s?t=3m22s and all he is doing is using no till and cover crops. As a smallholder, I can do things that he can’t. By incorporating green manures into an Emilia Hazelip approach, I minimally disturb the soil and constantly improve its tilth.

        We don’t use rock dusts – http://www.paramountgrowth.com/images/rockdust_sdiver01.pdf but will be trying a a side by side comparison this year.

        Regards,
        Mike

        Reply
        1. Deano Martin Post author

          Hi Mike
          I was impressed by the soil in the video from your link. That’s unusual for me, especially for an arable soil.
          I think that I’d prefer ‘sweet’ Lupin seed to large. There is a lot of ‘faff’ involved in preparing the larger seeds. Long soak, and a long boil. Perhaps we can do a swap next year, or I can get you some of the larger seed. it’s sold in specialist shops catering to Portugese people living here. http://www.portuguesefood.co.uk/index.php?main_page=product_info&cPath=33&products_id=87&zenid=22cf9d4f333dfee828b899c90992acc8
          After reading this again, I think that yours may be a better option.
          I’m about to do a side by side comparison of rockdust, but cannot be sure whether to do compost vs compost and rockdust, or compost versus rockdust and over wintered green manure. It would be nice to do all three, but not sure that I could organise it.
          Take Care
          Deano

          Reply
          1. MikeH

            Swap? Absolutely.

            It seems to me that any test with rockdust is probably best kept as simple as possible, ie, few variables. We’ll take one of our raised beds and add rock dust to one end of it while leaving the rest untouched. Then we’ll grow the same things in each section.

            Regards,
            Mike

          2. Deano Martin Post author

            My concerns with the rockdust experiment were mainly to do with the amount of space that would need to be used for direct comoparisons. If I use a bed for each, but grow a mix of the same crops in each bed, I can potentially avoid growing too much of one thing.
            Deano

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