Green Manure

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Aug 152009

Lupins photograph by Cecily Chenault

Not enthralled by the tastes of autumn and winter vegies? Broccoli and Cabbage not your thing? Then give something back to your soil. Plant a green manure crop to prepare for your spring vegetable beds.

Green manure is sown from seed usually in autumn and winter. It adds valuable organic matter to the soil, opens heavy and compacted soils, suppresses winter weeds, is an alternative to buying in compost to dig in and most importantly it ‘fixes nitrogen’.

Green manure is a crop that’s grown to purposely dig into the ground to improve the soil. Green manure is normally a plant from the pea family (called a legume) or has a legume in the mix. Legumes often used in a green manure are plants like peas, beans and lupins. It’s good to grow green manure crop every few years of as part of a crop rotation cycle. The lupins in the photograph above are close to being ready to be dug in as a green manure – as flowers are developing, but before seed is set.

We have a great mix available in our seed section, that seems to thrive in the cold when nothing much else wants to grow. It contains oats, dunn peas, lupins and rye corn.

It’s so easy to do, grab a bag and throw it generously around the area, rake it in a bit, water it and wait. You’ll see the green manure come up within a week. It’ll grow like crazy, if only the broccoli grew that fast!

Dig it in at flower fall (as flowering finishes, before seeds develop) or at least 1 month before your next crop. Chop it up and fold though with your spade. When you dig it in at flower fall, the plant is at it’s biggest and most nutritious before it starts to put it’s goodness into it’s seed. It’s important to give at least a month for the green manure to compost down in the soil before planting your next crop. Green manure grows well all through autumn and winter.

What does Fixing Nitrogen mean and what’s so good about it?

Legumes form a relationship with bacteria in the soil which then take nitrogen from the air and turn in into a form that plants can use. Nitrogen is a very important plant growth element. It gets used to grow lots of leaves and stems.

When you dig your green manure into the soil, the ‘fixed nitrogen’ is released as the plant breaks down. The nitrogen is then there for the next crop to use. Your next crop can be hungry spring and summer vegies like, tomatoes and corn, but green manure is also a great way to kick start a new garden bed for other plants too like trees and flowers.

Lupins photograph by Cecily Chenault