Ruud Kleinpaste: Green Manure

Green Manure? Don’t take that too literally – New Zealanders call fertiliser “manure.” 

Nature doesn’t like “bare soil”, so even in winter it will sprout seeds into plants, so why not make those plants desirable ones! 

We usually harvest our food crops in autumn, leaving behind a heck of a lot of soil, ready to be colonised by weeds. 

I realise we’re in mid-winter right now, but even at this time we can sow some plants that are experts at helping your garden become a lot more fertile in spring. 

The technique is quite simple: 

Green Manure crops literally extract some of the nutrients from the winter soil and store that in the stems (cells) and in the roots of the plant; 

Some green manure crops (the Legumes) have colonies of collaborative bacteria on board (in the roots) that can harvest Nitrogen from the air and store that in the root nodules too. 

Seeing the amount of Nitrogen in the air is 78%, we might as well use that stuff: Nitrogen (N) is essential for Leaf-growth – it literally creates the green matter that carries out Photosynthesis. 

Just a quick Science reminder: Photosynthesis is essential to keep us humans alive: the leaves of plants change Carbon-dioxide into Oxygen with the help of energy from the sun. We inhale that Oxygen and the exhale Carbon Dioxide 

The green plants basically do the opposite of how we breathe and keep everything in balance… 

Legumes that we can use (even right now) are clovers, lupins, beans, peas and fenugreek. Sow them in the fallow, and weed-free soil. 

The good thing is that they have a habit of quickly germinating and covering the soil before weed seeds come along 

These leguminose Nitrogen fixers are pretty efficient in grabbing the goodies from the air. 

Don’t let them go to seed as that will reduce the amount of N you can dig into your garden bed. Besides, seeds would create a weedy spring and summer, so avoid that. 

A good bed of Blue Lupins really covers the soil and prevents weeds germinating. 

Crimson Clover is one of those magnificently beautiful Legumes that also attracts pollinators. Generally speaking, the best time to dig your green manure into the soil is when it is flowering. 

In Sandy soils the Green manure works extra hard against loosing organic materials; Sand is notorious for loosing compostables quickly! 

In “Hard soils” the Green manure softens the soils by providing better soil structure. 

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