Lupin
Lupinus albus
Botanical family: Fabaceae
The genus Lupinus brings together Fabaceae with tall, upright flower spikes, grown as green manure (white lupin, Lupinus albus) or in the ornamental garden for their bright colours. Adapted to poor, acid lands where few legumes thrive, it enriches the soil with nitrogen.
Full sun
Acid, poor, light, dislikes chalk
Moderate, a plant of dry to cool soil
Variable depending on species (white lupin annual; perennial lupins hardier)
Overwinters in your zone
Role in permaculture
A Fabaceae with a deep taproot, the lupin captures nitrogen from the air and settles on the poor, acid soils that other green manures tolerate badly; it is reputed to loosen them, though the effect is not quantified here.
Insects attracted or useful
Documented synergies
Relationships backed by a named source, with their real scope. A synergy without a named reference has no place here, no “it is said that…”.
The lupin fixes atmospheric nitrogen, but with a symbiont apart: a Bradyrhizobium, not a classic Rhizobium. A crucial point for the gardener: measured in the field, most of the nitrogen fixed ends up in the SEEDS, very little in the residues left on the soil. If you harvest the seeds, the nitrogen leaves the plot with them. It's as a green manure mown before seed set, or as a preceding crop, that it enriches, not by harvesting.
scientific study
- · Kalembasa S. et al. (2020), Agronomy 10(9):1392, DOI 10.3390/agronomy10091392
- · Pueyo J.J. et al. (2021), Frontiers in Plant Science 12:644218, DOI 10.3389/fpls.2021.644218
The white lupin's real talent: faced with a phosphorus shortage, it forms 'proteoid roots', dense clusters of rootlets that exude organic acids, acidify the soil around them, and unlock the phosphorus fixed on iron, aluminium, or calcium. A very solidly documented mechanism. A caveat: the phosphorus actually made available to the FOLLOWING crop, in garden soil, has not been quantified, the measurements are in pots and hydroponics.
scientific study
- · Wang X., Pearse S.J., Lambers H. (2013), Annals of Botany 112(7):1449-1459, DOI 10.1093/aob/mct210
- · Sas L., Rengel Z., Tang C. (2002), Annals of Botany 89(4):435-442, DOI 10.1093/aob/mcf066
A subtle fact: fixing nitrogen costs a lot of phosphorus (the nodules are big consumers of it). In soil very poor in phosphorus, the lupin arbitrates, and therefore fixes less nitrogen. Its two assets, nitrogen and phosphorus unlocking, do not add up freely: they hold each other back. A lupin is not a magic wand that would deliver both lots of nitrogen and lots of phosphorus.
scientific study
- · Pueyo J.J. et al. (2021), Frontiers in Plant Science 12:644218, DOI 10.3389/fpls.2021.644218
A peculiarity: the lupin flower offers NO nectar, only pollen, and it takes an insect heavy enough, a bumblebee, to lower the keel and 'trip' it. Small bees can't manage it, and among the visitors, only the buff-tailed bumblebee group is really correlated with yield: visiting is not pollinating. As the lupin is mostly self-pollinating, this pollination remains a bonus. The authors advise offering other nectar sources around it, since it provides none itself.
scientific study
- · Fijen T.P.M., Morra E., Kleijn D. (2021), Agriculture, Ecosystems & Environment 313:107386, DOI 10.1016/j.agee.2021.107386
Seasons & availability
Sown in place early in spring, in March and April, or in autumn where winters are mild, lupin flowers in June and July, visited by bees; as a green manure it is cut and dug in before it runs to seed.
Available: April, May, June, July.
Guidance for the oceanic / temperate climate; it may vary with your region, altitude, exposure and growing method.
Sources
- La Ferme de Sainte Marthe, « Réussir la culture du lupin » (fermedesaintemarthe.com/en/blogs/comment-reussir-la-culture-de/reussir-la-culture-du-lupin)
- Plants For A Future, « Lupinus albus » (pfaf.org/user/Plant.aspx?LatinName=Lupinus+albus)
Nutritional & medicinal properties
For educational purposes. Not a substitute for medical advice. Effects depend on the form, the dose and personal context.
Precautions & contraindications
Bitter lupins contain toxic quinolizidine alkaloids: eat only 'sweet' seeds or ones properly de-bittered (repeated soaking). Lupin is a food allergen subject to mandatory declaration in the European Union, with possible cross-reactivity with peanut.
Family behaviour: Legumes
In general, Legumes fix nitrogen from the air in most cases, thanks to the Rhizobium in their root nodules. They mainly enrich the soil for the following crops, as their residues decompose. Ideal in a rotation, before nitrogen-hungry plants such as nightshades.
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Species & varieties
The best-known species and varieties in France.
Species
Voices of peoples
Paraphrases attributed to their documented sources. Never an invented quote.
Horace (Quintus Horatius Flaccus), Roman poet · Augustan Rome, around 20 BC
In an epistle, Horace praises the wise man who 'does not fail to know what distinguishes bronze coin from lupins'. Lupin seeds served proverbially as worthless tokens, opposed to real money. The fact attested by the text is precisely this proverbial use of the lupin as 'false money'. The explanation usually given for it, lupins are said to have stood for coins on the theatre stage, comes from the ancient commentators (scholiasts) and not from Horace himself.
Horace, Épîtres, I, 7, v. 22-23 («...nec tamen ignorat quid distent aera lupinis »), vers 20 av. J.-C. ; l'usage des lupins comme pièces de théâtre est rapporté par les scholies antiques (interprétation reçue).
An important distinction: the proverb of the lupin as a worthless token belongs to Horace's text, while the use of lupins as fake stage coins belongs to the interpretation of the scholiasts and is not ascribed here to the poet. The primary verse verified on Perseus. It's a symbolic and monetary use, with no medicinal or nutritional virtue at stake: no health claim is made here.
Key takeaways
- • Prefers full sun exposure.
- • Ideal soil: acid, poor, light, dislikes chalk.