Last autumn, I carefully cultivated a heap of seeds within a new garden bed, only to hack these fledgling plants down to the ground just a few weeks later – and deliberately let them all rot away.
It’s called “green manure” and it’s an easy way to build excellent soil for your veggies or fruit trees, at a very low cost.
Green manures don’t actually involve any animal manure at all. Instead, you create soil food and fertiliser from nothing more than plants.
Months later, when I dug into my once-depleted garden bed to plant the first of my fruit trees as part of my permaculture garden renovation, the soil colour had completely changed and the worm activity was off the charts.
And all from a pack of seeds that cost me less than five bucks.
Food gardening really is about growing soil: Cultivate great soil, and you’re much more likely to succeed with abundant yields and a tasty harvest.
So, here’s how to kick-start a new veggie patch or revitalise struggling soil by growing your own reen manure.
Koren’s hand holds a pile of summer green manure mix seeds
Green manure seed mix ready for planting.(Supplied)
Choosing the right seeds for your green manure
Cultivating green manure is very simple. You just sow a mixture of certain seeds, grow them for a couple of months, then chop it all down and allow those nutrients to decompose back into the soil.
But it’s crucial to use the right seed combination.
You can buy specific green manure seed mixes, which usually contain some kind of legume to help fix nitrogen, combined with cereal grain grasses to provide plenty of leafy green organic matter.
Most seed suppliers offer summer green manure packs and winter green manure packs — the mix of seed types changes a little depending on whether you’re growing in cool seasons or warm.
I used a summer green manure, which included mung beans, millet, soybeans, buckwheat and cowpea.
Common winter green manure mixes include lupins, fava beans, oats, subclover and woolly pod vetch.
How to plant your green manure crop
I’m a no-dig gardener, so I avoid turning over my soil — digging kills beneficial microbes and destroys the healthy, air-filled soil structure created by earthworms.
Instead, I lightly aerated and lifted my soil using a broad fork — sliding the fork into my soil to its full depth and then pulling the handle back about 45 degrees, without turning everything over.
Koren’s green manure garden two months after sowing
My green manure garden two months after sowing.(Supplied)
Then I added sifted homemade compost and biochar that I’d soaked in worm leachate for a few hours. The compost helps build organic matter in my soil, while the biochar will increase water retention.
After lightly raking the whole bed to work the compost into the top 10-centimetres of soil, I sprinkled my green manure seed mix over the top. Another quick rake helped cover the seeds.
Wild birds would love to gobble up all that seed, so I covered the whole area with old cotton sheet for about a week, until the seeds started germinating.
Finally, I gave everything a deep water — and the waiting process began.
When to ‘chop and drop’ your green manure
For the first week or so, I watered my green manure daily to help maximise seed germination — if seeds dry out as they’re sprouting, they will quickly die.
Once the seedlings were off and away, I removed the protective sheets and added netting overhead to provide further cover from wild birds.
Green manures generally need to grow for about eight weeks — enough time to create a heap of lush leafy growth but before any plants start flowering, at which point they’ll start taking nutrients from your soil.
So, about two months after sowing, it’s time to “chop and drop” the leaves.
the green manure about it’s been chopped and dropped
Fresh green manure after being “chopped and dropped”.(Supplied)
I chopped my green manure down using pruning shears, leaving the cut leaves dropped across the surface of my soil. I then aded a little pea straw on top to help my green manure break down.
You can plant directly into the soil at this point if you must, but it’s better to leave things for another month or so, allowing your green manure to decompose and return all those beautiful nutrients to your soil.
Helping my permaculture food forest thrive
My green manure has already done wonders for my soil. As the crop grew, it drew deep minerals to the surface and helped break up my hard-pan clay soil.
Once chopped and dropped, green manures increase organic matter, earthworms and beneficial microbes in the soil, while also boosting nitrogen levels and helping soil retain more water.
Koren stands proudly before her green manure garden bed
The extra months needed to build excellent soil will mean you’ll have delicious fruit and veg for years to come.(Supplied)
Veggies or fruit trees planted into this enriched soil are much more likely to thrive and produce a delicious harvest for you to enjoy and share.
In my ow urban backyard, I’ve now planted out my green manure bed with four fruit trees and plentiful perennial edibles underneath, including asparagus, strawberries, yam daisies and herbs.
This is permaculture food forest-style gardening, in which layers of perennials (plants that live for more than two years) are grown together to create a low-maintenance edible landscape.
Growing green manure before planting my perennials did require a few months’ extra patience, but it’s worth it in the long run – the extra effort to build excellent soil will help this patch deliver a delicious edible bounty for years to come.
Koren Helbig practices permaculture and grows organic food in the backyard of her small urban Tarntanya/Adelaide home.
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