A GREEN-manure crop will enrich winter growth once it's ploughed in.
The best way to enrich the soil during the cooler months is by sowing a green-manure crop in autumn.
First, let's explode a myth.
This stuff may be green, but it's not manure.
It isn't even a fertiliser, but is probably even more efficient for increasing soil fertility because it creates ideal conditions for the life within the soil.
So what is green manure?
It is a combination of leafy annual plants with special characteristics.
They are able to keep growing vigorously right through the coldest winter, despite chilly soil.
As the plants begin to mature in late winter and while still leafy and lush they are smashed down, chopped up and green sappy debris worked deeply into the topsoil.
Decomposition is rapid because the materials are so soft.
During this rotting process, it improves, lightens and aerates the soil, while providing food for earthworms, which breed and multiply at an extraordinary rate.
The intense tunnelling and feeding activity of earthworms, working with countless microorganisms, converts the decayed organic debris into a perfect, long-lasting fertiliser.
Consequently, even the most exhausted soils can become superbly fertile during winter when many beds are vacant.
What are these remarkable plants that make up a green manure crop?
They are quite common and the seed is easily obtained and cheap.
Best of all are mixtures of plain leafy plants, such as feed oats, wheat, barley, rye-corn and mustard.
In warm and sub-tropical districts, cheap parrot food such as black or grey sunflower seed can also be included.
Green-manure crops work even better if they are a selection of hardy, annual legumes such as grey peas, tic-beans (they look like broad-beans) and annual lupins. I also add half-used packets of last season's peas and broadbeans to the mix.
Legumes as green manure have a double benefit to the soil and to all nitrogen-hungry leaf vegetables grown the following spring and summer. These are the great creators of extra nitrogen, extracted from the soil atmosphere and fixed to legume roots as clusters of small, pale, grey nodules.
A combination of all green manure plants growing vigorously produce highly-active, deeply-probing roots that prevent winter soil from becoming cold and lifeless.
An extra-dense crop also smothers and suppresses winter weeds, so they too become a form of green manure. We can buy bags of specially mixed green-manure seeds from garden centres.
I'm a thrifty gardener, so I buy mine by weight from agricultural suppliers.
It costs far less and I can make up my own mixture.
Last year I transformed a piece of impoverished ground measuring 10m x 10m with a magnificent green-manure crop.
After roughly cultivating the surface - even using a heavy steel rake dragged over the surface does the trick - I sprinkled a good fistful of pelletised poultry manure over each square metre and raked it in.
My green manure mix consisted of one kilogram each of rye-corn, tic-beans, barley, wheat and annual lupins.
To this was added one cup of black mustard seed, plus the contents of some old seed packets.
After mixing in a bucket the seeds were broadcast evenly over the big bed. Finally, the loose surface was raked and cross-raked, so the seeds were either buried or at least dirtied.
Within two weeks - and after a good rain - the new plants were up and moving.
A few weeks later, I shovelled a barrow-load of sheep manure among the growing plants.
By late July, the tic-beans were chest-high and it was impossible to see the ground, so dense was the crop.
I got stuck into the lot with a rotary hoe and churned them in.
This summer, I grew silverbeet, tomatoes, capsicums, potatoes, pumpkins and summer brassicas with unbelievable yields from this previously barren ground.
And I've never seen so many earthworms, living proof of soil fertility and that green manuring is the way to achieve it.