Sweet Clover

A fragrant meadow plant known for its coumarin content, used historically as a forage crop, flavoring agent, and in European folk herbalism.

Last reviewed: February 9, 2026

Overview

Sweet clover (Melilotus officinalis, yellow sweet clover, and Melilotus albus, white sweet clover) is a tall, weedy biennial that grows along roadsides, in fields, and on disturbed ground across Europe and North America. The plant smells like freshly cut hay — a scent produced by coumarin, the same compound that gives tonka beans and new-mown grass their characteristic fragrance. Sweet clover has led a double life: agricultural workhorse and herbal curiosity. Farmers have used it as a soil-building cover crop and livestock forage for centuries. Herbalists have referenced it in a separate but parallel tradition. And the coumarin connection gives the plant an unexpected footnote in pharmaceutical history — the anticoagulant drug warfarin was developed after a coumarin-related compound in spoiled sweet clover hay was identified as the cause of a cattle bleeding disorder in the 1920s.

This page provides educational context on sweet clover's identity, traditional background, and safety considerations.

What it is

Sweet clover refers to the dried aerial parts (leaves, flowers, and stems) of Melilotus officinalis or Melilotus albus, harvested during the flowering period. It may appear as:

dried herb for brewing as tea or infusion
tinctures or liquid extracts
capsule or tablet supplements in some markets
an ingredient in some traditional flavoring applications (the coumarin content gives a vanilla-hay note)

The plant's signature compound is coumarin — present in all parts but concentrated in the dried herb. Coumarin itself is not an anticoagulant, but the distinction between coumarin and its degradation products is central to the plant's safety profile.

Traditional use (educational)

Sweet clover has a practical, agricultural identity alongside its herbal one:

European folk herbalism has referenced sweet clover in the context of circulatory comfort and leg heaviness, particularly in German and Eastern European traditions
the plant has been used as a cover crop and nitrogen-fixer in agriculture, valued for soil improvement
livestock forage use is extensive, though the connection to spoiled-hay toxicity gave sweet clover a cautionary agricultural reputation
the coumarin fragrance led to use as a flavoring agent in some traditional contexts — dried sweet clover was added to cheeses, tobacco, and sachets for its pleasant scent

These references describe cultural and historical use patterns, not proven clinical outcomes.

What research says

Research on sweet clover as an herbal preparation is limited. The plant's coumarin content has attracted phytochemical interest, but clinical trials specific to sweet clover tea or extract are scarce. The coumarin story is better studied in pharmaceutical and toxicological contexts — the discovery that dicoumarol (a degradation product formed when sweet clover hay spoils) caused hemorrhagic disease in cattle led directly to the development of warfarin. However, intact coumarin in properly dried, unspoiled sweet clover is a different compound with a different profile than dicoumarol, and conflating the two is a common error in popular discussions.

Safety & interactions

Common safety considerations include:

properly dried, unspoiled sweet clover consumed in typical tea amounts has a traditional track record, though formal safety studies are limited
the critical safety distinction is between coumarin (present in the fresh or properly dried plant) and dicoumarol (formed by fungal action when sweet clover hay becomes moldy) — dicoumarol is the anticoagulant compound, not coumarin itself
high coumarin consumption has been discussed in the context of liver sensitivity in some individuals, leading to regulatory limits on coumarin in food products in several countries
concentrated supplements or extracts carry higher coumarin exposure than simple tea preparations

Who should be cautious

Caution is commonly advised for:

individuals taking anticoagulant or antiplatelet medications (the coumarin/dicoumarol relationship, while commonly misunderstood, warrants caution in this population)
people with liver conditions or those taking hepatotoxic medications (coumarin has been discussed in the context of liver sensitivity at elevated exposures)
pregnant or breastfeeding individuals (formal safety data for concentrated preparations is insufficient)
anyone using sweet clover products that appear moldy, discolored, or improperly stored — spoilage is the mechanism that converts coumarin to the genuinely dangerous dicoumarol

Quality & sourcing considerations

Quality factors often discussed include:

proper drying and storage are critical — mold contamination converts coumarin to dicoumarol, fundamentally changing the safety profile
species identification matters — Melilotus officinalis (yellow) and Melilotus albus (white) are both used, but they are the specific sweet clovers of herbal tradition
products that appear damp, musty, or discolored may indicate the spoilage conditions under which dicoumarol forms
the distinction between simple dried-herb tea and concentrated extracts is relevant to both coumarin exposure levels and safety considerations

FAQs

Is sweet clover the same as red clover? No. Sweet clover (Melilotus species) and red clover (Trifolium pratense) are different plants from different genera with different chemistry. Sweet clover contains coumarin; red clover contains isoflavones. They are not interchangeable.
Is sweet clover dangerous because of warfarin? The connection is indirect. Warfarin was developed from dicoumarol, a compound formed when sweet clover hay spoils and becomes moldy. Properly dried, unspoiled sweet clover contains coumarin, not dicoumarol. The distinction matters, but the association has shaped the plant's cautionary reputation.
Is this page recommending sweet clover? No — this is educational information only.