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Nitrogen-fixers

Plants that enrich soil by fixing atmospheric nitrogen at their roots.

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All 80 nitrogen-fixers in the catalogue, alphabetical by common name. Each links to a full page with its ratings across the USDA, RHS, Canadian and Australian systems.

  • Albizia (Silk tree, Mimosa) Albizia julibrissin – Small ornamental tree with feathery foliage and pink powder-puff flowers across the canopy in midsummer. Fast growing but short lived. USDA zones 6–10
  • Alder — Common Alnus glutinosa – Riparian European tree, one of the few non-leguminous nitrogen fixers thanks to its Frankia root symbiosis. Bark is a traditional astringent for sore throats. USDA zones 3–7
  • Alder — Italian Alnus cordata – Heart-leaved southern European alder — faster growing and more drought tolerant than common alder, and equally happy on dry urban sites. A useful amenity tree. USDA zones 5–8
  • Alfalfa (Lucerne) Medicago sativa – Globally important forage legume with a taproot that can reach 15 m. One of the most efficient nitrogen-fixers and a powerful dynamic accumulator from deep soil layers. USDA zones 3–10
  • Alsike clover Trifolium hybridum – Short-lived perennial clover bridging white and red — pink-flushed flower heads, similar growth habit. Tolerates wet and acidic soils where other clovers fail. USDA zones 3–8
  • Astragalus Astragalus membranaceus – Chinese leguminous perennial. Roots ("huang qi") are a major immune tonic in traditional Chinese medicine; harvest 4+ year roots. USDA zones 5–9
  • Autumn olive Elaeagnus umbellata – East Asian shrub with silvery foliage and small red berries exceptionally high in lycopene. Once promoted for soil reclamation; now banned in many regions for its aggressive spread. USDA zones 3–8
  • Bayberry (Northern) Myrica pensylvanica – Eastern North American native shrub of coastal dunes and acidic heath. Waxy berries are the source of traditional bayberry candle wax. USDA zones 3–7
  • Bird's foot trefoil Lotus corniculatus – Sprawling European perennial with bright yellow pea-flowers fading to orange and seed pods arranged like a bird's claws. A meadow staple supporting many butterfly species. USDA zones 3–8
  • Black locust Robinia pseudoacacia – Fast-growing North American leguminous tree. Wood is one of the most rot-resistant timbers in temperate climates — fence posts last 50+ years. Heavy nitrogen fixer. USDA zones 3–8
  • Black medic Medicago lupulina – Low-growing annual or short-lived perennial in the alfalfa genus. Often turns up uninvited in lawns — usefully so, since it tolerates compacted soil and adds nitrogen. USDA zones 3–9
  • Black she-oak Allocasuarina littoralis – Eastern Australian coastal native casuarina. Critical food plant for the glossy black cockatoo, which feeds almost exclusively on its seeds. USDA zones 8–11
  • Black wattle Acacia mearnsii – Fast-growing Australian wattle widely planted as a commercial tannin source. The bark contains the highest commercially viable tannin concentration of any common species (28–40%). USDA zones 8–11
  • Blackwood Acacia melanoxylon – Large southeastern Australian acacia producing premium dark cabinetry timber. Tolerates more shade than most acacias and supports a wide range of native moths and butterflies. USDA zones 8–11
  • Bladder senna Colutea arborescens – Mediterranean shrub with yellow pea-flowers followed by inflated, papery, parchment-like seed pods that pop when squeezed. Tolerates poor and alkaline soils. USDA zones 5–8
  • Bog myrtle (Sweet gale) Myrica gale – Aromatic wetland shrub of UK and northern European bogs. Used to flavour beer (gruit) before hops became standard, and a traditional Scottish midge repellent. USDA zones 1–6
  • Bristly locust Robinia hispida – Suckering eastern North American shrub or small tree with bristly stems and rosy-pink racemes of pea flowers in early summer. Useful for stabilising poor soils. USDA zones 5–8
  • Broad bean (Fava) Vicia faba – Cool-season legume sown autumn through early spring. Nitrogen-fixing roots make it a useful cover crop and follow-on partner. USDA zones 3–9
  • Buffalo berry — Silver Shepherdia argentea – Thorny silver-leaved shrub of the North American prairies and northern plains. Tart red berries are an Indigenous food source, traditionally sweetened after the first frost. USDA zones 2–7
  • Carob Ceratonia siliqua – Long-lived Mediterranean tree producing leathery dark pods used as a chocolate substitute and as livestock feed. Drought-tolerant; nitrogen-fixing roots. USDA zones 9–11
  • Chinese bayberry Myrica rubra – Subtropical Chinese tree (yangmei) with juicy, sweet-tart dark red fruit. USDA zones 8–10
  • Coastal she-oak Casuarina equisetifolia – Tropical and subtropical pioneer she-oak of coastal sands across the Australian, Pacific, and Indian Ocean tropics. Tall, narrow, salt- and wind-tolerant — among the great pioneer beach windbreak species. USDA zones 9–12
  • Common vetch Vicia sativa – Fast-growing annual legume — the standard small-scale green manure across much of Europe. Autumn-sown in mild climates, spring-sown in cold. USDA zones 3–9
  • Cootamundra wattle Acacia baileyana – Fast-growing southern NSW endemic wattle to 8 m with fine silvery-blue ferny foliage and abundant fragrant golden ball flowers in late winter. Outside its small native range, a notorious invader. USDA zones 8–10
  • Coral tree (Cockspur) Erythrina crista-galli – Small ornamental South American tree producing vivid red papilionaceous flowers in late summer. National flower of Argentina and Uruguay. USDA zones 8–11
  • Cowpea (Black-eyed pea) Vigna unguiculata – African and Asian legume serving simultaneously as warm-season green manure, fast-establishing cover crop, and edible pulse. Drought tolerant once established. USDA zones 3–12
  • Crimson clover Trifolium incarnatum – Tall annual clover with deep crimson flower heads — striking enough to be ornamental as well as agricultural. A staple winter cover crop in orchards. USDA zones 5–9
  • Crown vetch Securigera varia – Mediterranean perennial with pink-and-white pea-flower heads. Aggressive ground cover historically planted on highway embankments for erosion control. USDA zones 3–9
  • Desmodium (Tick trefoil) Desmodium spp. – Tropical and subtropical legume genus widely used in cover-crop systems. Best known as the "push" companion in African push-pull pest management for maize. USDA zones 7–11
  • Drooping she-oak Allocasuarina verticillata – Small to medium southeastern Australian native she-oak with strongly drooping weeping foliage and dark furrowed bark. A tough drought- and frost-tolerant inland windbreak across southern Australia. USDA zones 8–11
  • Dyer’s broom (Dyer’s greenweed) Genista tinctoria – Low spreading British native broom relative with bright yellow pea-flowers in summer. Whole flowering shoots produce a clear yellow dye, the traditional partner to woad for medieval green cloth. USDA zones 2–8
  • False indigo (Wild blue indigo) Baptisia australis – North American prairie native with deep blue lupine-like flower spikes in late spring. Long-lived and architectural — a permanent garden feature once established. USDA zones 3–9
  • Fenugreek Trigonella foenum-graecum – Fast-growing annual legume — Indian culinary herb (methi), a galactagogue medicinal, and an excellent warm-season green manure with a distinctive maple-syrup scent. USDA zones 2–11
  • Field pea (Forage pea) Pisum sativum var. arvense – Cool-season cover-crop pea — smaller seed and habit than garden pea (P. sativum), grown for biomass and nitrogen fixation rather than fresh eating. USDA zones 2–9
  • French bean (Green bean) Phaseolus vulgaris – Tender warm-season legume in dwarf (bush) and climbing forms. Nitrogen-fixing roots benefit following crops. USDA zones 2–11
  • Goat's rue Galega officinalis – European perennial herb that yielded the chemistry behind metformin — the most-prescribed type-2 diabetes drug in the world. Pale lilac pea flowers attract bees. USDA zones 4–8
  • Golden wattle Acacia pycnantha – Australia's national floral emblem — a small tree producing dense balls of brilliant yellow flowers in late winter and early spring. USDA zones 8–11
  • Gorse Ulex europaeus – Spiny European shrub flowering nearly year-round in mild climates. A working European hedge plant — and one of the most aggressive invasive weeds outside Europe. USDA zones 7–9
  • Goumi Elaeagnus multiflora – East Asian shrub bearing tart bright-red speckled berries. Used in Japanese culinary traditions; significantly better-behaved than its invasive cousin autumn olive. USDA zones 4–9
  • Grey alder Alnus incana – Hardy pioneer alder of cold and dry sites where common alder will not thrive. Fixes nitrogen via Frankia bacteria and improves poor soils. USDA zones 2–7
  • Hairy vetch Vicia villosa – Winter-hardy annual or biennial vetch — the cover crop of choice for no-dig systems. When crimped at flowering, creates a dense mulch mat that the next crop is planted directly into. USDA zones 3–9
  • Honey locust Gleditsia triacanthos – Large North American legume with feathery foliage, sweet edible pods, and dappled shade — popular as a street tree because grass grows beneath it. USDA zones 3–9
  • Kakabeak Clianthus puniceus – New Zealand native scrambling shrub with elegant pinnate leaves and pendant clusters of large brilliant scarlet beak-shaped flowers in spring. Among the most striking of all native New Zealand plants. USDA zones 8–10
  • Kentucky coffee tree Gymnocladus dioicus – Long-lived North American legume with bold compound foliage and brilliant yellow autumn colour. Roasted seeds were an early-American coffee substitute. USDA zones 3–8
  • Kowhai Sophora tetraptera – Iconic small New Zealand tree with cascading clusters of bright yellow tubular flowers in early spring — the country's unofficial national flower. USDA zones 8–10
  • Lablab bean (Hyacinth bean) Lablab purpureus – Vigorous tropical climbing legume with ornamental purple flowers and pods. Fast-growing summer cover crop and a vegetable in many cuisines, but raw beans are toxic. USDA zones 3–12
  • Laburnum (Golden chain) Laburnum anagyroides – Small European tree with spectacular pendulous racemes of yellow flowers in late spring — the famous Laburnum Arch at Bodnant Garden being the iconic example. USDA zones 5–8
  • Leadplant Amorpha canescens – Low silvery-grey prairie shrub with deep purple flower spikes contrasting against the foliage. A cornerstone plant of North American prairie restoration. USDA zones 2–9
  • Lentil Lens culinaris – Cool-season pulse crop and one of the oldest cultivated plants — domesticated 9,000+ years ago in the Fertile Crescent. Excellent rotation crop for cereals. USDA zones 3–10
  • Leucaena Leucaena leucocephala – Fast-growing tropical legume tree used widely as livestock fodder, firewood, and a nitrogen-fixing nurse plant. Coppices reliably. USDA zones 9–12
  • Licorice Glycyrrhiza glabra – Mediterranean leguminous perennial. Sweet roots are a major anti-inflammatory and demulcent in both Western and Chinese traditions; harvest after 3+ years. USDA zones 6–9
  • Lupin — Blue (Narrow-leaf) Lupinus angustifolius – Annual lupin grown widely as a grain crop in Western Australia and as a cool-season cover crop elsewhere. Modern "sweet" cultivars are low-alkaloid and edible. USDA zones 3–9
  • Lupin — Russell hybrid Lupinus × regalis – Garden hybrid lupin in a vivid range of colours — pink, white, yellow, blue, red, bicolour — bred from George Russell's seedlings in 1930s Yorkshire. USDA zones 4–8
  • Lupin — White Lupinus albus – Mediterranean annual lupin grown for centuries as a pulse crop. Seeds are debittered by soaking before being eaten — the basis of Spanish, Italian, and Egyptian street snacks. USDA zones 3–9
  • Mesquite Prosopis spp. – Drought-adapted southwestern North American shrub or tree. Pods ground into mesquite flour for baking; deep taproot can reach groundwater 50 m+ below the surface. USDA zones 7–11
  • Millaa millaa Elaeagnus latifolia – Vigorous scrambling subtropical shrub with tart-sweet red fruit; fixes nitrogen. USDA zones 9–11
  • Mountain mahogany Cercocarpus montanus – Drought-adapted shrub or small tree of the western North American mountains and high deserts. Distinctive feathery seed plumes in autumn are an unusual ornamental feature. USDA zones 4–9
  • Pea Pisum sativum – Cool-season legume in shelling, mangetout, and snap forms. One of the earliest spring vegetables; declines in heat. USDA zones 2–9
  • Pigeon pea Cajanus cajan – Short-lived shrubby legume — perennial in subtropical climates, grown as an annual elsewhere. Seeds are the basis of Indian dal; deep taproot breaks compacted soil. USDA zones 3–12
  • Red clover Trifolium pratense – Pink-purple flowering legume long used as a forage crop, nitrogen-fixing cover crop, and herbal source of phytoestrogenic isoflavones. USDA zones 3–9
  • River she-oak Casuarina cunninghamiana – Tall evergreen Australian native of riparian zones. Casuarinas resemble pines but are flowering plants — cone-like fruit, drooping needle-like branchlets that whisper in the wind. USDA zones 8–11
  • River wattle (Bower wattle) Acacia cognata – Elegant weeping eastern Australian wattle with fine narrow drooping phyllodes ("leaves") and small fluffy pale yellow ball flowers in spring. Compact cultivars (‘Cousin Itt’, ‘Limelight’) are now landscape mainstays. USDA zones 9–10
  • Royal poinciana (Flame tree) Delonix regia – Large tropical tree producing spectacular orange-red flower clusters across the entire canopy in summer. Madagascan origin; widely planted across the tropics. USDA zones 10–12
  • Runner bean Phaseolus coccineus – Climbing bean with bright red (or white) flowers and long flat pods. A British staple of cottage and allotment gardens. USDA zones 3–11
  • Russian olive Elaeagnus angustifolia – Silver-leaved Eurasian small tree historically planted as windbreak across the North American Great Plains. Cold and drought hardy, but invasive in much of its introduced range. USDA zones 2–8
  • Sainfoin Onobrychis viciifolia – Pink-flowered chalk-loving European legume. The non-bloating clover alternative for ruminants and the source of one of the world's most prized monofloral honeys. USDA zones 3–8
  • Scotch broom Cytisus scoparius – European shrub with masses of bright yellow pea-flowers in late spring. Highly invasive in many regions outside its native range. USDA zones 5–8
  • Sea buckthorn Hippophae rhamnoides – Thorny silver-leaved shrub bearing dense clusters of tart bright-orange berries. Berries have exceptional vitamin C and E content; growing commercial bushfood interest. USDA zones 3–8
  • Siberian pea shrub Caragana arborescens – Extremely cold-hardy Mongolian and Siberian shrub. One of the toughest nitrogen-fixers for prairie shelterbelts; edible seeds and yellow pea-flowers. USDA zones 2–7
  • Silver wattle Acacia dealbata – Tall fast-growing Australian acacia with feathery silver foliage and intensely fragrant yellow ball flowers — sold in European florists as "mimosa". USDA zones 8–10
  • Spanish broom Spartium junceum – Tall Mediterranean shrub with rush-like green stems and intensely fragrant yellow pea flowers. Traditional source of textile fibre across southern Europe. USDA zones 7–10
  • Subterranean clover Trifolium subterraneum – Self-regenerating annual clover with the unusual habit of pushing its own seed underground after flowering. The backbone of southern Australian dryland pasture. USDA zones 7–10
  • Sunn hemp Crotalaria juncea – Tropical Asian legume — perennial in true tropics, grown as an annual elsewhere. Reaches 2 m in 60 days, producing extraordinary biomass for nitrogen fixation and mulch. USDA zones 3–12
  • Sweet clover — White Melilotus albus – Tall biennial legume with intensely fragrant white flower spikes. A major honey plant and one of the deepest-rooted dynamic accumulators of any cover crop. USDA zones 3–9
  • Sweet clover — Yellow Melilotus officinalis – Yellow-flowered counterpart of white sweet clover with similar habits. Historically used as a wound herb in European folk medicine; same intense vanilla-coumarin scent when dried. USDA zones 3–9
  • Tagasaste (Tree lucerne) Chamaecytisus palmensis – Fast-growing Canary Islands shrub or small tree. A staple of Australian permaculture for livestock fodder and rapid nitrogen-fixing in dry regions. USDA zones 8–11
  • True indigo Indigofera tinctoria – Tropical shrub historically the world's premier source of natural blue dye — driving global trade for centuries until synthetic indigo replaced it in the 1880s. USDA zones 9–11
  • Wax myrtle (Southern bayberry) Morella cerifera – Southeastern US evergreen shrub of coastal areas. Salt-tolerant, fast growing, and wildlife-friendly — a workhorse for southern coastal gardens. USDA zones 6–10
  • White clover Trifolium repens – The standard low-growing clover of lawns and pastures across temperate regions. Tolerates mowing, fixes nitrogen, and feeds bees — the original "lawn clover" before postwar herbicides erased it. USDA zones 3–10
  • Woolly pod vetch Vicia villosa subsp. dasycarpa – Heat-tolerant subspecies of hairy vetch suited to Mediterranean and Australian climates. Same nitrogen-fixing benefits with better summer survival. USDA zones 5–10

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