Sweet clover

Value to bees

Nectar

Very high

Pollen

High

As a honey crop

Major honey crop — yields a surplus in good years

Which bees, and why

Worked heavily by everything. Its importance is best understood against alfalfa: both are prairie legumes, but sweet clover's shallow accessible florets make it a honey crop where alfalfa's tripping mechanism makes it a pollination problem.

Small shallow pea flowers with nectar within a honey bee's reach — the key difference from alfalfa and red clover.

Worth knowing

Very high nectar over a long dry-season window, and shallow enough florets that honey bees can work it properly — which alfalfa, growing in the same fields, will not allow.

Flowering

In flower

June to August (northern hemisphere)

A long window, and unusually drought-tolerant — sweet clover keeps secreting through hot dry summers when other prairie forage stops.

When nectar flows

Copious and dependable, and it goes on for weeks because the long spikes open in succession from the bottom upwards.

Year-to-year variation

Among the most reliable major honey plants in North America, and a substantial crop across the northern plains and Canadian prairies.

What it does to the honey

Coumarin carries into the honey as a genuine sweet-hay and vanilla note, which is what separates sweet clover honey from ordinary clover honey and is the clearest coumarin character in any common honey.

Growing it

Conditions

Full sun, any drained soil including poor and alkaline ground. Deep-rooted and drought-tolerant.

Size

60-200 cm in the second year.

Native range

Europe and central Asia, naturalised across North America, Asia and Australasia.

Suits

Meadow or wildflower area, Farm scale, Large gardens

• Biennial: sow two years running and it self-perpetuates thereafter.
• Useful in a green manure or herbal ley mix, where it fixes nitrogen and feeds bees at once.
• Coumarin becomes a genuine problem in spoiled sweet clover hay, where mould converts it to dicoumarol, an anticoagulant — this is how warfarin was discovered, from cattle bleeding to death after eating mouldy melilot.

What it looks like

A tall branching biennial with trifoliate leaves and long slender spikes of small yellow or white pea flowers, the whole plant smelling strongly of hay when cut or crushed.