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How to improve your soil

How to improve your soil
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The key to a good garden is good soil – and there are a number of ways you can improve it no matter where you live. One way is to grow green manures. They’re a short-term crop specifically grown to be dug back into the soil, adding much needed organic matter and nutrients.

Here’s our take on how to improve your soil:

There are six main advantages from growing green manures:

  • They add organic matter to the soil which helps improve its fertility
  • They help make nutrients available to any plants that are grown in the soil afterwards
  • They prevent nutrients from being washed through the soil in winter (known as leaching)
  • They suppress the growth of weeds
  • They help break up heavy soils, improving drainage
  • They protect the soil from pounding rain in winter which can cause a hard layer to form on the surface.

The only drawback with green manures is that you have to let the ground fallow (leave alone) while the green manure is growing. In the vegetable garden, this is easy as it’s usually separated into clear sections, so an area can be put aside to grow green manures.

In a more ornamental part of the garden, it can be a bit more impractical or undesirable to leave unproductive areas of soil for a length of time. However, Lupins can be used as green manures, so you could have a beautiful display of them.

Adding fertility to your soil

Apart from adding organic matter, some green manures offer other benefits. For example, deep-rooting green manures such as Alfalfa, Red Clover and Lupins will use nutrients from deeper in the soil (beyond the reach of many crops). Then when the green manure decomposes in the soil, the nutrients are deposited in the upper layers where the follow-on crops and plants can use them.

Similarly, leguminous plants like beans, Lupins, Clover and Fenugreek, have special nodules on their roots filled with ‘nitrogen-fixing’ bacteria that can take nitrogen from the air and make it available to the green manure. Again, when the green manure decomposes, the nitrogen then becomes available to follow on crops and plants.

Choosing a green manure

There’s a good range of green manure crops, which one you choose depends on when you intend to plant it and how long you’re prepared to leave it growing before incorporating it into your soil. For most people, green manure that can be sown in late summer or early autumn and left to grow over the winter would be best. Clovers or ryegrasses are perfect for this and will have time to grow before digging in during early spring.

In heavy soils (like clay or silt), digging during early spring is not a good idea because it will damage the soil structure. So try a tender quick-growing crop like Buckwheat or Fenugreek instead.

If you have a new garden or a barren plot that you don’t intend to cultivate or plant for at least a year, then one of the longer-term green manure crops, such as Alfalfa or Alsike clover is worth sowing. If you find that you’re ready to tackle the area earlier than expected, these green manures can be dug in at any time. Just leave a few weeks for them to rot down before planting.

Which green manure?

Common name(Latin name)When to sowGrowing timeWhen to dig in
Alfalfa(Medicago sativa)Late spring3-24 monthsAny time while fresh
Buckwheat(Fagopyrum esculentum)Spring to late summer2-3 months