Fields of yellow: Sweetclover springs up in southwest ND

Vast swaths of common, yellow-flowered sweet clover are springing up along southwest North Dakota roadsides and ranges, thanks to early spring rains.
Despite its simple beauty, sweet clover saps up precious water because of deep roots.
It can also become a menace to ranchers as it encroaches on more palatable forage sources, Dickinson Research Extension Center range scientist Llewellyn Manske said.
A biennial plant, which reaches maturity after two years, sweet clover needs 36 pounds of water to produce one pound of dry matter, Manske said.
“That is sucking out the water that could be producing beneficial plants,” Manske said. “It hurts everything else.”
By comparison, oats and barley need five to seven pounds of water, while alfalfa and Kentucky bluegrass use 12.
According to a North Dakota State University extension publication on sweet clover, the plant can withstand harsh winters and droughts. It can also endure 10 days of flooding without suffering serious losses.
A highly competitive nature supports peak growth between four to five feet, Manske said.
Farmers and ranchers can control rampant growth with herbicide 2,4-D, he said.
Dickinson Research Extension Center cattle specialist Doug Landblom said he invites sweet clover growth, as it is a sign of a good year for hay production.
The towering plants can also provide shade to other grasses in its shadow, protecting them from the sun’s rays on hot days.
“You might not see it again to this extent for a number of years. Then again, you might see it again in two years. It depends on the weather,” Landblom said.
Manske said sweet clover is used for cattle and horse feed by some ranchers, especially when the plant is young. But, it remains generally “hard to stack, hard to bail, difficult to feed.”
“You have to take advantage of what you can if it can provide food,” he said.
If left in a bale or haystack for too long, mold can grow, which can be just as poisonous as rat poison, Manske said.
Bowman rancher Brent Mrnak said his cattle generally stay away from sweet clover because of its bitter taste.
“They’re not interested in eating it, especially when it gets to a certain stage,” Mrnak said.
Manske said a common misconception exists that a sweet clover always replenishes nitrogen in soil it is planted in. But west of North Dakota’s 20-inch rainfall line, this is not true.
“All of the legumes, like sweet clover and alfalfa, growing west of the 20-inch rainfall line use more nitrogen than they fix,” Manske said.
According to the state extension service, herbicides only kill sweet clover for the duration of a year, but dormant seeds continue to produce for as many as 20 years.
“It comes and goes,” Landblom said. “There’s not too much you can do about it.”