Every June there is a wash of yellow along the edge of almost every highway and trail in North America. The yellow is from sweet clover that grows and blooms all across the continent. It’s wild and it has been reseeding itself, year after year, for centuries. The yellow biennial (there’s a white variety, too) is an amazing honey plant and was once celebrated as the weed that saved Kentucky from economic ruin, as you will see shortly.
Sweet clover is one of the sweetest weeds you’ll ever meet. A century ago, farmers in Indiana and Illinois (and other states) planted sweet clover for hay. It escaped their fields and spread along the nation’s highways, occasionally helped by other farmers who captured the seeds and planted the weed in their own fields. Planting sweet clover to enrich fields and provide livestock forage has waned. The last time I saw yellow sweet clover intentionally planted in a field was during the 1970s, in southern Saskatchewan, Canada.
I can’t say enough good things about sweet clover. The yellow variety brightens the scenery and announces summer. Sweet clover replenishes soil, ‘fixes’ nitrogen, as farmers call the process where this element is sucked from the air and stuck into the dirt. Farmers once plowed millions of acres of sweet clover into the ground – the plant’s bushy fiber mulched, fertilized, and enriched the soil. Here is what Ag scientists told South Dakota farmers in 1925:
SWEET CLOVER was once considered only as a weed, but now  it is held a very valuable crop. This deep-rooted, vigorous-growing, hardy, biennial legume surely has a place on South Dakota farms. It has no equal as a combined soil-building, weed-fighting, pasture and hay crop.
Sweet clover is a most important crop in a successful system of crop rotation in South Dakota. It is a legume and our farms must have more acres of these crops. Its large, deep-growing roots add much valuable nitrogen and vegetable matter to the soil, thus improving the soil on which it grows; it endures dry weather and still produces valuable pasture and hay; it successfully competes with the weeds that rob our other crops; it reduces the acreage of small grain crops and it improves the quality, yield and profit of the crops that follow it. Surely such a crop, when properly used, has a place on the farms of South Dakota.
Since 1925, sweet clover has been replaced by less natural fertilizer and isn’t seen much in cultivated fields. Yet even today, sweet clover’s deep roots prevent erosion on hillsides. Those tap roots keep the plant alive during drought, giving noms to wildlife even when the rest of the landscape is burnt and sere. Most important of all, I think, is the fact that sweet clover is a fantastic honey plant – one of the best in the world.
With all this to commend it, you may be surprised to learn that the Canadian government pays summer students (mostly budding ecologists) to destroy sweet clover. It’s been labeled a noxious, invasive weed. I’ll get to that in tomorrow’s blog post, but I’ll spend the rest of today praising the honey bees’ best friend.
Beekeepers in ancient Greece recognized sweet clover as a wonderful honey plant. It still attracts bees by the millions to the steep, dry hillsides where it flourishes. Long after Aristotle swallowed his last chunk of clover honeycomb, scientists searched for a scientific name to tag to sweet clover. They chose Melilotus – from Greek words that celebrate honey (meli-) and lotus, which they somehow thought sweet clover resembles. (Even scientists goof up occasionally.) Sweet clover has a long history as a renowned honey plant.
How good is it? Melilotus nectar averages 52% sugar and just 48% water. Most nectar is 20% sugar and 80% water. The 52%-sugary nectar was sampled in North Dakota on a dry summer day. You can see the advantage to the bee – each belly-load carries twice the sugar as typically found in other honey plants. Honey supers fill twice as fast. It takes fewer trips and bees process it more easily during nectar’s conversion into honey.
Sweet clover is found nearly everywhere, but it does best in the lime soils of the American plains and Canadian prairie, secreting particularly well on sultry summer days. As mentioned, it’s drought-resistant – but prefers about 16 inches (40 cm) of annual rainfall. This moisture is typical on the plains. In drier climates, sweet clover hugs irrigation canals.
Sweet clover yields enough nectar to make 250 to 500 pounds of honey per acre (Pellet, 1920 and Kolbina, 2007). Millions of pounds of honey are lost each year, simply because there are not enough honey bees to gather all the nectar secreted by the world’s sweet clover. For beekeepers, dropping 20 colonies near a section of sweet clover doesn’t begin to touch its potential.
Sweet clover is now found throughout the world, but is native to north Africa, Europe, and west Asia. In those places, over a dozen species of Melilotus are found. Four have invaded North and South America, Australia, Oceania, southern Africa, and eastern Asia. Sweetclover was assisted in its travels by humans, who have cultured the yellow (M. officinalis) and white (M. alba) biennials since 1738 in North America. We generally treat yellow and white sweet clover as one plant with two hues – they are similar, but not totally identical. Yellow sweet clover blooms two weeks before its pale cousin, but I don’t think the honey is noticeably different.
Sweet clover was imported to North America from Europe. It spread across the continent from east to west. During the 1700s, it was mostly confined to the east coast. The plant likes alkaline soil and doesn’t do well in the east, where acidic soil abounds. But – as you see in the picture above – it can grow quite well in some eastern localities, such as Pennsylvania limestone strip mines, where the soil is alkali. My father used to haul hundreds of hives to catch a July sweet clover honey flow each year. As a child, I remember that other beekeepers were baffled because our family produced white sweet clover honey when most of them had only reddish autumn goldenrod, made from the spiky plant that thrived in the local acidic soil. They hadn’t caught on to moving hives into the old limestone quarries where the clovers grew, then moving back to the goldenrod for the fall flow.
In the 1800s, sweet clover crossed the Appalachian Mountains. Shortly after the first American Civil War (1860s), it was still just taking root in Kentucky. Here’s a story from Frank Pellet’s 1920 honey plant book. Pellet tells us about the day sweet clover came to a poor, rural part of Kentucky:
“One of the pioneer growers [of sweet clover] was E. E. Barton, and his experience with it sounded like a fairy tale. Mr. Barton said that following the Civil War, most of Pendleton County was given over to tobacco growing, with little live stock, and not much rotation of crops. It was a hill country, and although it had a fertile soil over a clay subsoil, the heavy rains soon washed away the shallow surface soil, and one farm after another was abandoned. Hundreds of farms were abandoned, and many of them were sold for taxes, because no buyers could be found. More than a third of the population left the county, and the farmers who remained had hard lines to make ends meet. Sweet clover was stealthily sowed, probably by beekeepers intent on increasing the bee pasturage. At first it was regarded with disfavor and fought as a dangerous weed.
“Mr. Barton came into possession of a farm, somewhat against his will, because the owner could not pay the mortgage. He tried renting it, and the tenant was unable to make a living, much less pay the rent. After it had been abandoned, he went to great trouble to keep down the weeds, especially sweet clover. Then came a year of drought, when there was very little feed for the cattle, and they were turned into the roads to graze.
“Even there there was but little except the sweet clover, which was by this time rather common along the roadsides. It was soon noticed that the cows were eating the sweet clover with relish and doing well. Then somebody tried an experiment by sowing it in a field. It thrived, the cows liked it, and the milk flow was increased. Mr. Barton by this time was quite ready to profit by the experience, and within five years the farm which would not grow grass was producing good crops. He bought more abandoned farms and sowed them to sweet clover, and his neighbors began to do likewise. One by one the farmers came back to their abandoned farms, new settlers came in, and everybody began to grow sweet clover.
“Now there are fifty thousand acres of it in that county. Ask any farmer you meet on the streets of Falmouth what he thinks of sweet clover and he will tell you such tales of rebuilt fortunes from a combination of dairy cows and sweet clover as you never expect to hear. There are now shipped from the county about half a million pounds of seed yearly, besides thousands of dollars’ worth of dairy products every week. They find that an average of 300 to 600 pounds of hulled seed per acre can be secured from the white variety and 500 to 700 pounds of the yellow. An average yield of from $40 to $100 per acre is the return from the sweet clover, according to local reports picked up on the streets. Now one finds evidences of prosperity on every hand. The farmers have fine homes, automobiles, and money in the bank.”
By reading Frank Pellet’s tale of how sweet clover saved Kentucky from chaos and economic ruin, you can see that it is a plant worthy of unending praise. Pellet’s little essay doesn’t mention that Kentucky also became one of America’s great honey states in the late 1890s, mostly because of the arrival of sweet clover. In 1900, at least 50,000 Kentucky farms had bees – they totaled over 200,000 hives.
By the 1920s, sweet clover had spread through most of Kansas and was crossing the Dakotas. It became established in southern Saskatchewan just 40 years before I kept bees there in the 1970s. By then, sweet clover matched alfalfa as the honey plant that gave me 300-pound per hive honey crops. But that same area – southern Saskatchewan – is also the place where the government is now attempting to eradicate sweet clover – seen as an invasive pest, a noxious weed. It’s not the farmers who want it gone, it’s the government. Tomorrow we’ll look at the debate and see how eradication is going.
What a wonderful plant and so tall. It’s not like the short white and red clover that grows in our British grass.
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It can reach 2 metres. But it is sometimes much shorter, especially when chewed back by antelope. You’ll see that in tomorrow’s piece.
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Hi Ron, I wonder if you have a reference for the 52% sugar content you mention for yellow sweet clover? I am trying to make sense of the entry in Eva Crane’s honey book, in which the “sugar value” for both white and yellow sweet clover appear low – for instance, about 1000x lower than for borage, or even apple. Digging into it a bit, the “sugar values” values in Crane are calculated nectar yields per flower, not sugar concentrations. The original work was done by Polish researchers in the 1950s and 60s. I wonder if the values for sweet clover are per individual floret rather than the whole flower spike? In any event I have always understood that sweet clover has both high sugar content and honey productivity. Any additional info appreciated – and I really enjoy your blog entries.
Rob in NB
The number 52% is from the book 100 Plants to Feed the Bees: Provide a Healthy Habitat to Help Pollinators published by the Xerxes Society, which references sweet clover this way:
You can see a more detailed reference in Some nectar characteristics of certain world honey sources (1985, Pszczel. Zesz. nauk. 29:29-45), which you will find in PDF format on the Eva Crane Trust website at this link. That meta-analysis cites a 1973 paper from Battaglini et al., which shows an entry for Melilotus officinalis (yellow sweet clover). They show that it secretes 0.11 mg/flower/24hr with 0.06 mg of sugar. That’s 0.06/0.11 = 54% sugar concentration in the nectar. Battaglini also says that the flower yields 10-300 kg/ha (a range of about 9 to 270 pounds/acre). By the way, to answer one of your questions – I think 0.11 mg is what would be collected from a single floret.
I’m sure you noticed that really low number (9 pounds) – sometimes sweet clover secretes almost nothing. It does very poorly at yielding nectar in acidic soils and in damper cooler environments. I’m not sure how well it will do in New Brunswick.
With regards to the ‘sugar value’ being 1/1000 of that of borage or apple, I had a quick look at Eva Crane’s A Book of Honey but didn’t notice that mentioned. I have the 193-page 1980 copy. If you can send me the page number, I’ll look for it.
Hi Ron, thanks for the reply, including more useful information. The other reference you noted, ‘Some nectar characteristics of certain world honey sources’, is especially useful, as it separates out the sugar concentrations specifically. The stats that are presented as sugar value per flower are potentially misleading if they are based on individual florets of what can be large composite flowers, as of course the total nectar available will be determined by the number of the florets (as well as the nectar secretion rate). I am convinced of the value of sweet clover, and have grown both white and yellow types. Both grown well on roadsides in New Brunswick, but as far as beekeepers are concerned there is never enough of it. Last year I experimented with some sweet white, variety “Hubam” which is supposed to bloom in year one, but I think our season here is too short to allow for that, as mine did not.
In terms of comparing the nectar of Melilotus to apple, borage etc the data I was looking at is from Table 2.123 of Crane’s ‘Honey, A Comprehensive Survey’ that starts on p. 85. The data there are sugar values, or sugar secreted/24h. I think the apparently large discrepancy between Melilotus and the other species must be explained by the data being based on secretion per floret in the case of Melilotus.
Many factsheets on Melilotus note that it does best on alkaline soils, which we lack here in the Maritimes. Isn’t it interesting how so many outstanding nectar plants in North America are deemed to be invasive weeds? Dandelions, loosestrife, Japanese bamboo, sweet clover….
I grew up in western Pennsylvania, along the Appalachians. The soil there was acidic. My father once took 20 hives to a nearby farm that had half a section of white sweet clover, head-high and blooming beautifully. The bees made no honey at all. Then he figured out about the soil type and made contact with a strip-mine just north of Pittsburgh where limestone was produced and sold to the area’s steel mills. They let him put bees there. The whole area was covered in sweet clover and we took a couple hundred hives in there every year, making a modest (60 pounds) or so each July when other area beekeepers were feeding their bees through the summer dearth. Soil type is really important.
I like your last comment – non-native plants in North America (dandelions, purple loosestrife, sweet clover, alfalfa, dutch clover, canola, chinese tallow, and many others) are really outstanding nectar sources for our non-native honey bees. It makes sense. North American plants and North American bees (like bumblebees) evolved to work together while in Europe, North Africa, and the Middle East, honey bees (which are native to that area) evolved to exploit the native dandelion, clovers, etc. To me, it is more surprising (and maybe troubling) that our imported bees work some native plants really well – such as tulip poplar and fireweed. This must affect the native bees somewhat. However, tulip poplar secretes cups of nectar per flower (just a slight exaggeration) and fireweed (willow herb) also occurs in Europe so we can see why those native plants attract honey bees (but most native American flowers don’t attract honey bees).
Saw a news article lately that ND remains top honey producing state. Guess why. The soils are alkaline. The acreage of sweet clover is huge – particularly from the center of the state on west.
A favorite memory is of driving a road during a cooling evening where the clover has been mowed, swathed, conditioned and curing. The scent is of nirvana.
Clover doesn’t stand alone with the bees brought there. There are great expanses of flax and both oil and confectioners sunflowers. In certain areas alfalfa occupies many acres. Many see the state as just flat and boring. All depends upon what you know and look for.
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I’ve driven through North Dakota a dozen times and always found it beautiful and memorable. It’s been a long time since vast acres of sweet clover were seeded, but the plant is ubiquitous on hillsides and road allowances (where it still ends up baled).
Thanks for sharing your memory and observations.
Ron, and readers, what is the flavour profile of Sweet Clover honey? I just did an extraction of what I think must be Melilotus honey (don’t think anything else is blooming here right now) and it was very dark, with a very sweet, almost flat flavour, with caramel notes.
I produced sweet clover honey in Pennsylvania, Saskatchewan, and Alberta. In each case, the honey was white to water-white and very mild in flavour. Honey may vary depending on soil type, rainfall, soil nutrients – but I doubt your ‘very dark’ honey is sweet clover. There are some labs able to analyze the honey’s pollen (for a fee), if you really want to know.
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