Green manures

Green Manures

Green manures are plants that are grown specifically to cover and protect the soil between harvests, while helping to improve structure and fertility.

In natural environments, soil is always covered. This protects it from erosion and guarantees a food source for the microbes all year round. Bare soil is not healthy soil, and covering it ensures that:

• you are building new soil
• your soil is being fed by the process of photosynthesis
• any weeds are being suppressed by plant cover.

There are many types of green manure (see the table at the end of this chapter for our favourite varieties) and each one offers a different benefit to the soil below.

Some green manures, such as alfalfa, are nitrogen fixers. This means they help to draw atmospheric nitrogen (known as N2) out of the air and convert it into a form that's accessible to plant roots.

Meanwhile, other green manures like fodder radish have long tap roots that can help to aerate the soil.

All of them create biodiversity in your garden too, and will encourage insects, birds and other wildlife to visit.

Why Not Try?

• You can sow green manure at pretty much any time of year (except in the depths of winter).
• Why not overwinter green manures in your garden by sowing them in autumn? Particularly good winter varieties include Hungarian grazing rye and forage rye.

Cutting It Down

We sowed two of our favourite green manures, mustard and Phacelia, at the end of February. By late April they were well established.

If you want to, you can leave your phacelia to flower first, as bees absolutely love it. Just make sure to cut it back before it sets seed, otherwise it'll quickly take over your bed.

There are two ways of processing your green manures when you're ready to use your bed: crimping or cutting back.

Cutting Back

Cutting back green manures doesn't mean you have to uproot them. In fact, leaving the roots in the ground means that you are not disrupting your soil and the roots can be eaten by the microbes below.

When cutting back our green manures, we use Jakoti shears and cut back the plants to the lower part of the stems. By cutting them low down, you can plant your seedlings or seeds amongst the stubble, which will eventually die back while your seedlings grow upwards.

Save your fresh leaves to add to your compost cakes (we'll show you how to make these later in this course).

Planting Seedlings Into the Stubble

• Phacelia is an annual, so once it's cut back, it won't regrow.
• The roots will dissolve as they are eaten by the microbial life in the soil.
• You can plant seedlings into this patch - filling each hole with a pinch of climate compost before planting.
• We prefer to use a copper trowel for this job as they're lightweight and may even prevent slugs.

Sowing Buckwheat

Another option when growing green manures is to leave them in situ for just a few weeks. These small seedlings will still provide cover and nutrients for the soil, but they will be small enough to just hoe into your bed when you are ready to plant.

Alternatively, you can leave buckwheat to seed as the seeds are an edible, gluten-free grain.

Sowing Buckwheat Into the Stubble

You can sow buckwheat directly into the stubble of a previous green manure or sow it directly into bare soil.

• Mix the buckwheat seeds (known as groats) with a handful of climate compost and rub the seeds into the mix.
• Sow the seeds first thing in the morning or early in the evening. Sowing on an overcast day is preferable to protect the microbes in the compost.
• Broadcast the seed and compost mix over your space.
• Rake them into the surface of the soil using a rake; this will provide a bit of soil cover and help them to germinate.
• Water in using a watering can with a rose attachment.

Crimping the Mustard

Instead of cutting back our mustard, we crimp it. To crimp your plants, simply push them over with a rake and flatten against the soil.

This creates a living mulch on the surface of the soil. The foliage will start to brown off and die back, before being taken down into the soil by microbes and earthworms.

To create a thicker mulch, you can also cover your crimped plants with a layer of compost. After a few weeks you can then plant seedlings directly into your mulch.

Be warned though - as these two layers break down, they will generate heat, so don't plant anything too delicate in this mulch. We tend to plant heat-loving crops like lettuce into ours. More delicate plants will not be able to cope with the high temperatures generated.

Our Favourite Green Manures

Here's a list of our favourite green manures, including the best months to grow them in and some of their key benefits for your soil.

| Green manure | When to grow? | What does it do? | Why we love it |

|--------------|---------------|------------------|----------------|

| Alfalfa | April to July | Nitrogen fixer, deep roots break up compacted soil | Frost hardy, so can be overwintered too |

| Buckwheat | April to August | Fast growing and unlocks phosphate in the soil | Bees love its white flowers and you can eat the seeds too |

| Crimson clover | March to August | Excellent weed suppressor | Beautiful crimson flowers, great for bees |

| Fenugreek | March to August | Boosts fertility and suppresses weeds | A member of the legume family, so it fixes nitrogen too |

| Fodder radish | May to August | Good for compacted soils as it has long tap roots | Quick growing, but it's a brassica so make sure to rotate |

| Forage rye (Hungarian grazing) | August to October | Nitrogen fixer and weed suppressor | Good choice for overwintering |

| Mustard | March to September | Great for suppressing weeds | Quick grower, but it's a brassica so make sure to rotate |

| Phacelia | March to September | Quick growing, only 2 or 3 months until flowering | Beautiful flowers, which bees love |

| White clover | March to August | Great for suppressing weeds and for long-term use | Fixes nitrogen in the soil |

| Winter tares (vetch) | March to May or July to September | Fixes nitrogen and great for sowing under taller crops all year round | Frost tolerant so can be overwintered, but watch out, it doesn't like dry or acidic soils |

| Yellow trefoil | March to August | Shade-tolerant nitrogen fixer | Low growing, so great for growing under crops - but watch out, it seeds quickly |

Why Not Try?

• Try experimenting with green manures in your garden.
• At the beginning of the year, buy all the seed varieties you think you'll need and create a sowing timetable.
• It's worth sowing green manures whenever your soil is bare. Even if they only provide cover for a month or so, they will still be feeding your soil microbes with vital nutrients.