Green Manure – Not as Bad as it Sounds

The first time I heard the words ‘green manure’ the mental image in my head wasn’t particularly appealing. I’m sure someone could come up with a better term for it! Sometimes it is actually referred to as a cover crop, but cover crop is a less specific term as it isn’t necessarily something you will dig into the soil. If you think about green manure in the sense of what you use manure for in the garden, not what comes out of the cow in the paddock, then the mental image is not so bad…

In autumn I sowed mustard seeds over a good chunk of the vege garden. This is my green manure crop, which has a few purposes. When dug into the soil it will provide the vege garden with some much-needed organic matter. It will also help to suppress weeds, which are a major issue for the garden at the moment, and help to protect the soil from being washed away or compacted while there aren’t any crops in it over winter. There are a number of plants that you can use for a green manure crop, including various grains, lucerne, crimson clover, blue lupin, phacelia and mustard, or you can use a mixed crop. Some of these crops just add good organic matter into the soil when dug in, while others have additional ‘special abilities’ such as drawing up nutrients from deep in the soil, fixing nitrogen from the air, breaking up hard ground and providing food or shelter for beneficial insects. What you choose as a green manure will also be dependent on what time of year you want to grow it and what crops you intend to grow in the soil after it. For those in NZ, Kings Seeds is a good place to check out and buy seeds from.

Mustard (Brassica alba).

The fascinating and intelligent reason why I chose to use mustard is because I already had a bag of mustard seeds. Wow, so deep! But the main reason I bought it in the first place is because it can be sown in autumn to grow through winter when not much else is growing and Bunnings had bags of it. Mustard’s special abilities include fast growth and good weed-suppressing. I have also read that it helps to rid the soil of wireworms, which can be a problem for potatoes, and harmful soil fungi. You are supposed to let mustard grow for somewhere between one and three months before chopping it down. The longer you leave it the more fibrous it will become and will be harder to break down. It should also be dug in before flowering, unless you want some seed to save. Cut it to ground level then dig it in. You can leave it on top of the soil for a few days before digging in.

Last weekend I asked The Husband, “Can you cut the mustard?” He was too busy playing a computer game to appreciate my wit. However, while I was busy hauling out weeds in the front garden, he did go out and cut the mustard for me with the weed-eater. This past weekend I dug it into the soil. This is not a particularly fun job but I felt very satisfied with myself once I had finished. I’m sure the soil will soon be happier too. Now I must wait for at least two weeks before I plant anything there to allow the organic matter to decompose sufficiently so as not to burn the plants. One thing about mustard it that it is in the brassica family. This means brassicas, such as cabbages, cauliflower and bok choy, should not be planted in this area during the season after the mustard crop, as mustard can spread the diseases that all brassicas like to share with each other, like clubroot. I’m still figuring out what to grow where, but one thing I will be growing after the mustard is garlic. The shortest day has just passed, meaning we are in garlic-growing season, and hopefully in two weeks’ time, I will have acquired some seed garlic to plant.

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