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11 Nitrogen Fixing Green Manures

As well as suppressing weed growth and improving soil structure some green manures have the ability to fix nitrogen. Nitrogen is vital for plant growth and soils deficient in nitrogen will produce poor crops at best.

Nitrogen can be added as an artificial fertiliser or via organic fertiliser like dried blood. It is also in manures and composts. Over time it decreases in the soil, winter rains in particular wash nutrients from the soil.

Nitrogen fixing green manures will, in conjunction with bacteria, absorb nitrogen from the air and fix nitrogen in the soil. When the plant is dug in, that nitrogen is available to the following crops. Free fertiliser!


This list is taken from SowSeeds and links the nitrogen fixing green manures to the relevant page on the SowSeeds web site for further information and to buy, of course. SowSeeds offer discounts on top of their low price on bulk buying and also mixed seed packs of green manures. Images Copyright © SowSeeds


Alfalfa Green Manure

Alfalfa (Lucerne) Green Manure By Elekes Andor –  CC BY-SA 4.0

Alfalfa Green Manure

Alfalfa (Lucerne) is a very deep rooting green manure with vigorous roots that can draw up sub-surface minerals and break up soil pans.

It is can overwinter once well established and will grow for a year or more. Alfalfa Green Manure dislikes acid or wet soils but does well in dry conditions

Sow: April, May, June, July

Alfalfa Green Manure Seeds


Crimson Clover Green Manure

Crimson Clover Green Manure

Crimson Clover Green Manure

Crimson Clover Green Manure is a good choice for smothering weeds, fixing nitrogen from the air and is a fast growing bulky green manure. It has deep roots that penetrate the soil and bulky furry foliage that once dug in helps to improve soil structure.

Sow: April, May, June, July, August, September

Crimson Clover Green Manure Seeds


Fenugreek Green Manure

Fenugreek Green Manure

Fenugreek Green Manure

Fenugreek Green Manure is a quick growing annual that can be ready to dig in 10 weeks from sowing. It can be sown from March to August and performs best on well-drained but slightly heavy soils. It will tolerate lighter ones if they are fairly moist.

Sow: March, April, May, June, July, August

Fenugreek Green Manure Seeds


Lupins Green Manure

Lupins Green Manure

Lupins Green Manure

Lupins are a hardy annual green manure that can be planted from March to July and are part of the legume family. They suit light sandy acid soils and are a hardworking leguminous plant that has very long tap roots that dredge up minerals.

Sow: March, April, May, June, July, August

Lupins Green Manure Seeds


Red Clover Green Manure

Red Clover Green Manure

Red Clover Green Manure

Red Clover is a fast growing perennial green manure. It is the best variety of clover for fixing nitrogen from the air, weed suppression & improving soil structure. Its roots penetrate deep into the soil and help to improve its structure by binding soils together (especially light ones)

Sow: April, May, June, July, August, September.

Red Clover Green Manure Seeds


Sweet Clover Green Manure

Sweet Clover Green Manure

Sweet Clover Green Manure

Sweet Clover ‘Yellow Blossom’ is an aggressive green manure that grows rapidly and has very strong roots that penetrate hard compacted soils that helps to improve drainage. It also produces lots of leafy foliage that adds good organic matter to the soil when dug in which improves soil structure.

Sow: March, April, May, August, September.

Sweet Clover Green Manure Seeds


White Clover Green Manure

White Clover Green Manure

White Clover Green Manure

White Clover ‘Barblanca’ makes as excellent long-term green manure. It has good frost tolerance and once established can last from 2-5 years. White Clover makes a good weed suppressant as it produces a fair amount of foliage and is able to fix nitrogen.

Sow: March, April, May, June, July, August

White Clover Green Manure Seeds


Winter Tares Green Manure

Winter Tares Green Manure

Winter Tares Green Manure Seeds

Winter Tares ‘Vicia sativa’, also known as ‘Vetches’ is a hardy annual that can be sown March-May or July-September for over-wintering. It is good at nitrogen fixing and for weed suppression on heavier soils but avoid acid or dry soils and dig in before flowering.

Sow: March, April, May, July, August, September.

Winter Tares Green Manure Seeds


Yellow Trefoil Green Manure

Yellow Trefoil Green Manure

Yellow Trefoil Green Manure

Yellow Trefoil ‘Black Medick’ is a low growing green manure that has excellent weed suppressing properties. It is good at fixing nitrogen and if allowed to flower encourages bees & beneficial insects to the area which in turn pollinate veg crops. Yellow Trefoil is great for interplanting taller crops

Sow: March, April, May, June, July, August

Yellow Trefoil Green Manure Seeds


Field Bean Green Manure

Field Bean Green Manure

Field Beans Green Manure

Field Beans are an overwintering green manure and is generally winter hardy. It germinates well in colder weather from September-November. Field Beans are particularly good on heavy soils and their deep roots are not only able to penetrate & break up the soil but fix nitrogen too.

Sow: September, October, November

Field Beans Green Manure Seeds


Forage Pea Flower Green Manure

Forage Pea Flower Green Manure

Forage Pea Green Manure

Forage Pea Green Manure is a member of the legume family that is excellent at fixing nitrogen and has deep penetrative roots that help to break up the soil. It can grow up to 1 metre tall. Forage Pea is excellent for over wintering and can be sown from September.

Sow: September, October, November

Forage Pea Green Manure Seeds


More on Green Manures

Green Manure: Guide To Sowing & Growing Green Manure

Green Manure: Guide To Sowing & Growing Green Manure

Which green manure to grow and when, what to do when it's grown? This guide explains the basics of using green manures to improve your soil
Green Manures - Uses & Types of Green Manures

Green Manures - Uses & Types of Green Manures

Green manures are a wonderful way to add and retain nutrients to the soil whilst improving the structure. They can even save time as they suppress weeds.

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