Melilotus albus Seeds | White Sweet Clover
LATIN NAME: Melilotus albus
COMMON NAME: White Sweet Clover
Plant Profile
White sweet clover is a tall, upright, branching biennial of the pea family, and the height usually quoted for it needs correcting: it grows one to two metres tall in a good season, not five to ten metres. The first year produces a deep taproot and a rosette of trifoliate leaves; the second year sends up the flowering stems, sets seed and dies.
The leaves are typical of the clovers, with three leaflets, toothed at the tip, and they carry a sweet, hay-like scent when crushed or dried. The stems are slender, wiry and much branched, and they hold the plant upright without support even in wind, which is one reason it was grown as a fodder crop on light land.
The flowers are small, white, pea-shaped and borne in long, slender racemes that open from the bottom upward through summer. A flowering plant is covered in them, and the scent carries a long way, which is how the plant got its common name. The pods that follow are small, oval, wrinkled and usually single-seeded, and they are produced in enormous numbers.
Its native range covers Europe and Asia, and it has been carried around the world as a forage and green manure crop. It is now naturalised across North America, Australia, New Zealand and southern Africa, where it grows on roadsides, railway embankments, disturbed ground and dry pasture, and it is regarded as an invasive weed in several of those places.
Science & Biotechnology
The scent and the toxicity come from the same chemistry. White sweet clover contains coumarins, mainly melilotoside, which break down to coumarin when the plant is crushed or dried, giving the sweet hay smell. In damp, poorly cured hay, fungi convert the coumarin to dicoumarol, a potent anticoagulant that causes internal bleeding in cattle. That discovery in the 1920s led directly to the development of warfarin and the modern anticoagulant drugs.
The plant is a vigorous nitrogen fixer, and it was grown for that reason before synthetic fertiliser. It nodulates with a range of rhizobia, it produces a deep taproot that penetrates compacted subsoil, and it can add a hundred kilograms of nitrogen per hectare in a good stand. It is one of the classic green manure species, and it is still used to improve poor, dry land.
The seed is hard-coated and long-lived, and it can remain viable in the soil for decades. That is the reason the plant is so difficult to eradicate once it has set seed, and the reason it appears in disturbed ground long after the last flowering plant was removed. Scarification or a hot-water soak is needed for reliable germination.
Taxonomically the species is close to yellow sweet clover, Melilotus officinalis, and the two hybridise. Some authorities treat them as a single variable species, and the distinction rests on flower colour, the shape of the pod and the wing petals. The white form tends to be taller and later flowering than the yellow.
Uses & Benefits
As a forage and green manure crop, the plant is genuinely useful. It is grown for hay, for silage and for grazing, and it is sown to improve poor, dry, stony land, where its taproot and its nitrogen fixation do work that no fertiliser can. It is also a major bee plant, and honey from sweet clover is one of the classic mild monofloral honeys of North America.
The medicinal history is real but narrow. Melilot, the dried flowering tops, was used in European herbal medicine as an anti-inflammatory and a mild anticoagulant for varicose veins and for swelling, and it appears in some European vein preparations today. The coumarins are the active compounds, and the risk of interaction with anticoagulant drugs is genuine. The plant should not be used without medical advice.
The culinary use is limited to flavouring. Coumarin has a sweet, hay-like taste and was used in the past to flavour cheese, tobacco and soft drinks, but it is now restricted in food in many countries because of liver toxicity at high doses. The plant is not eaten as a vegetable.
Ecologically, the species is a mixed blessing. It is an excellent nectar source and a nitrogen fixer, but it is also an aggressive coloniser of disturbed ground, and it can dominate a restoration site and delay the establishment of slower native species. In a garden, it should be grown only where it can be cut before it sets seed.
Growing from Seed
Scarify the hard seed by nicking the coat or by soaking in hot water for a few minutes, then leave it in warm water overnight. Sow one centimetre deep in a loose, free-draining mix at fifteen to twenty degrees, and expect germination in two to four weeks. Untreated seed can sit for years, so scarification is worth the effort.
Sow directly where the plant is wanted, since it resents transplanting once the taproot has formed. It grows on almost any soil, including poor, dry, stony ground, and it needs full sun. Cut the flowering stems before the seed sets if you do not want it to spread, and pull the plants in autumn after flowering, since they are biennial and will die anyway.
Our Take
White sweet clover is a plant with two faces: a valuable forage and bee crop that fixes nitrogen and improves poor land, and an invasive weed whose coumarins can kill cattle and interact with blood thinners. Grow it if you have a reason, cut it before it seeds, and do not brew it as a home remedy.
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