Nitrogen Fixers and Nutrient Cyclers - Page currently under construction

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Most nitrogen fixers need good light to give them the extra energy to feed the micro-organisms in nodules on their roots that do the actual fixing. Although some plants may tolerate shade this will be at the expense of nitrogen production.

It follows that they also need the right micro-organisms on their roots, so I have sorted them as natives, to the UK, and non- natives. Most natives will have no problem finding suitable partners in natural soils. The non-natives are selected for their ability to find the right partners in our soils. If necessary nodules can be transferred from plant to plant as follows:

Find a plant of the same species with good nodulation.

Collect nodules from around the roots - these will be not be far from the air.

Place nodules in a liquidizer with a little rain water or spring water [ tapwater is usually harmful to bacteria].

Liquidize for a few seconds - the nodules should be broken up.

Mix with a few litres of non-tap water and water your new plants with the solution.

If it works the plants will be greener and more vigorous in time.

Nitrogen Fixing Trees

Alders all do very well on wet or moist soils, some are also good on dry soils. Generally windfirm, good on heavy clay and tolerate coastal exposure. Alders do not share pests and diseases with major crop-tree species, so are useful as windbreaks and shelterbelts. Most may be trimmed as hedges, yielding rich trimmings for mulch or compost. Fast growing in the early years. Most alders stand soil and air pollution. Good as bird food - small seeds are released over a long period during autumn and winter.

Italian Alder - Alnus cordata

Does well on wet or dry soils, as good as Robinia on dry sandstone. Height after 20 years about 20 metres.

 

Common Alder - Alnus glutinosa

The UK's native alder. A tree of damp or wet soils and in drier soils usually dying with the first major drought. Oygenating roots will penetrate compacted and waterlogged soils. Height about 18 metres after 20 years. Some ornamental forms exist.

Grey Alder - Alnus incana

Sub-polar tree standing colder and drier soils than Common Alder. Much used in land recovery schemes. Suckers close to the base and may grow to make a thicket. Coppices easily.

Red Alder - Alnus rubra

From the US west coast and performing well in the milder parts of the UK.

Green Alder - Alnus viridis

A naturally shrubby Arctic and Alpine species worth a trial on our own degraded uplands.

Black Locust - Robinia pseudoacacia

The best of the pea family trees in the UK, the 'Acacia' of suburban Acacia Avenues. Very fast growing and windfirm. Trees sucker many metres from the parent so best in open spaces. Large thorns. White flowers sweetly scented and liked by bees - 'Acacia' Honey. Wood has a very high calorific value so a good choice for firewood. Timber very durable and strong. Used for hen forage in areas where it seeds copiously. Leaves insecticidal.

Laburnum is another very good n-fixer, and frequently self sows, but is not stocked due to its toxicity.

Nitrogen Fixing Shrubs

Native Shrubs:

Broom - Cytisus scoparius

Usually leafless- the green stems do the job of the leaves. Likes well drained, acid to neutral soil and full sun. Stands cutting and will regrow from the base, though generally not long ;lived. Stands wind. Unopened flowers edible. Good wildlife plant. To 3 metres.

Prostrate Broom - C.s.maritimum - a native, sprawling, horizontal form of Broom found on the coast. Stems root readily in contact with soil. Should be useful for stabilising and feeding loose soils. Edible flowers as above.

Gorse - Ulex europaeus

Evergreen spiny dense shrub to 2 metres. Likes an acid soil and full sun, and will sprawl to avoid shade. Very good nurse shrub and barrier plant, will deter deer. Too sprawling for a neat hedge but there is an erect form 'Stricta'. Flowers edible and available nearly year round, coconut scented. Burns fiercely and readily, not recommended near buildings.Good wildlife plant.

Dyer's Greenweed - Gensta tinctoria

Low deciduous shrub to 60 cms or so. We stock the variety ' Royal Gold '. Vivid yellow broom-like flowers start July and last till midwinter. A natural constituent of grassland and scrub on heavy soils. Ancient dye plant and good for wildlife.

Sea Buckthorn - Hippophae rhamnoides

Large spiny deciduous shrub of sand dunes and alpine areas. Narrow grey green leaves and orange berries. Suckers, especially on sand. Plants are dioecious - i.e. either male or female, so both sexes needed for fruit. Berries have a sharp, lemony acidity and are used in drinks and preserves. To 3 metres on exposed sites, more in sheltered areas. Our basic wild stock is unsexed.

Cultivated forms of Sea Buckthorn:

Sweet Gale - Myrica gale

Low shrub of peat bogs and acid heaths, to about 1.3 metres. Grey-green leaves and golden catkins in early spring. Another dioecious shrub, i.e. plants are either male or female. Spreads by suckering. Needs a permanently moist soil. All parts have a pleasant resin scent and it has been used as a flavouring and tea, though it should be used with caution as it may induce abortion.

 

Non-native shrubs

Siberian Pea Tree - Caragana arborescens

Deciduous shrub to 4 metres, usually less. Edible flowers and green pods. Plants liable to mollusc attack even when quite mature - they are fond of the green bark. Nodulation variable - some plants seem to be unable to find suitable bacterial partners.

Elaeagnus - Decicuous or evergreen shrubs or small trees, fast growing, windfirm and drought resisting. They are capable of fixing large amounts of nitrogen. Most have an edible fruit, often sweetish. Flowers are sweetly scented and attractive to bees. Evergreen types flower in the Autumn and their fruit ripens in the spring, when few fresh fruits are around. They are indifferent to soils, except waterlogged, and they stand air pollution, factors making them favoured for civic planting schemes. They have great potential and deserve further selection and development.

Russian Olive, Oleaster - Elaeagnus angustifolia

Large deciduous shrub or small tree to 7 metres. Greyish long leaves. Good as a windbreak, stands coastal exposure. Small but abundant yellow flowers. Fruit sweet, dry and mealy and used for sherbets and jellies. Wood hard and a good fuel. Stands heavy pruning.

Varieties: - 'Caspica' has elliptical, very silvery leaves, sometimes sold as 'Quicksilver'.

 

Elaeagnus x ebbingei - a hybrid of E.macrophylla and E. pungens.

Large evergreen shrub to 5 metres but usually about 2 to 3 metres. Tolerates quite heavy shade under trees so useful as an understorey weed supressor and as a filler at the base of windbreaks. Fruiting in spring it is used by pheasant raisers as a combined cover and feed crop. Resists salt winds and will trim to a hedge, so very useful as a coastal windbreak. Attractive foliage and sweetly scented flowers in the autumn. Fruit about 2cm long, variably sweet and juicy when ripe, astringent till then.

Thorny Elaeagnus - Elaeagnus pungens

Medium evergreen, slightly spiny shrub from Japan, where it has many traditional medecinal uses. Not quite so hardy as the others here, it may be damaged by very hard frosts. Usually seen in cultivation as variegated forms. Flowering in autumn, fruiting spring. May cross pollinate with E.x ebbingei, giving higher yields and interesting offspring.

Autumn Olive - Elaeagnus umbellata

Large deciduous shrub to 5metres. Another Asian species with many medecinal uses. Several cultivars developed for ornament and fruit but hard to find. Fruit a red berry with silver dots, sharply acid, similar taste to Sea Buckthorn.

Tree Lupin - Lupinus arboreus

Small/medium evergreen shrub to 2 or 3 metres, with yellow lupin flowers. Naturalised in S.Britain, stands coastal exposure and is used for stabilizing dunes. Needs a well-drained soil and full sun. Not long lived and liable to be killed by severe winters, although it produces copious seed and will self sow in the right soils. Seedlings grazed by slugs. Bee plant. Blue/mauve flowered form also available.

Wisteria - pea family woody climbers

Chinese Wisteria - Wisteria sinensis

Woody climber to 10 metres. Familiar ornamental, fast growing. 30cm long racemes of fragrant mauve flowers, which are said to be edible when cooked. Very useful for adding interest and nutrients to windbreaks and tall hedges - will climb into tall leylandii. Prefers a moist alkaline to neutral soil but will grow and survive on acid sands.

Herbaceous N-fixers

There are very many of these including all the peas, beans, clovers and lupins. We stock 2 perennial native trefoils, both are good wildlife plants and feed larvae of Skipper and Blue butterflies.

Bird's Foot Trefoil - Lotus corniculatus

Attractive low perennial, making a carpet about 30 cm across. Yellow/red edible flowers - 'Bacon and Eggs'. Central tap root goes deep and it avoids drought when surrounding grasses are brown. A major nitrogen fixer - it has been developed into several agricultural forms. Suits most soils. Our plants are from seed of native wild stock, some collected locally.

Greater Bird's Foot Trefoil - Lotus uliginosus

Similar to above but larger in its parts and a plant of moist/wet soils. It is often the greenest plant in the marsh, sometimes covering small drier areas, showing you where to walk. Will scramble into taller plants, and ditch grown specimens may go 2 metres up into an adjacent hedge.