Sorghum halepense Seeds | Sorghum Grass
LATIN NAME: Sorghum halepense
COMMON NAME: Sorghum Grass, Johnson Grass
Plant Profile
Johnson Grass is a tall, rhizomatous grass of the Mediterranean region and western Asia, growing to two metres with broad leaves and open, plumelike seed heads of reddish spikelets. It is the wild, running relative of grain sorghum, and it spreads both by seed and by sharp white rhizomes that push up new shoots all season.
It was introduced to the United States as a forage grass in the nineteenth century and repaid the favour by becoming one of the world’s worst weeds, now listed as noxious in many jurisdictions. Anyone considering sowing it should first check local law, because in much of North America and Australia it is prohibited.
Science & Biotechnology
Its relationship to sorghum is the interesting part: Sorghum halepense is a tetraploid that hybridises with cultivated sorghum, Sorghum bicolor, and the resulting hybrids complicate both weed control and crop breeding. It has also evolved resistance to several herbicide groups, which keeps it in the weed-science literature.
Like its crop relative it contains dhurrin, a cyanogenic compound: young growth after drought or frost can poison grazing stock, which is one of the practical reasons the species is managed rather than sown. Field studies of its rhizome depth record shoots from thirty centimetres down, which is why surface cultivation only breaks the rhizomes up and spreads the plant.
Uses & Benefits
Where it is legal it is used as forage and erosion cover on warm, droughty ground, cut rather than grazed when young. Its real horticultural interest is as a comparison: gardeners who see it run can understand why sorghum-sudan forage hybrids are sold for the same purpose without the rhizomes.
Its seed heads feed granivorous birds through autumn, and its deep, drought-proof root system has a genuine value on erodible ground, a value the weed lists have weighed and found wanting. Its identity is also a lesson in common names: in some regions the name Johnson grass is applied to other weedy sorghums, so confirm the species before any control programme. In its dry Mediterranean home it is a plant of seasonally wet hollows, which explains both its drought armour and its habit of appearing wherever water collects.
Growing from Seed
Sow the seed in late spring once the soil is warm, a centimetre deep in ordinary soil; this is a heat-loving grass and cool sowings sit still.
No cold treatment is needed; germination takes one to two weeks in warmth, and growth is fast from the start.
If grown at all, grow it in a container or a confined plot, cut it before the seed ripens, and dig out the rhizomes at the season’s end; a missed season is how the problem starts. Fluazifop or digging are the controls that work; hoeing the surface merely multiplies it. Seed for study is best gathered into paper bags in the field and dried at once, since the seed holds well in storage and remains viable for years.
Our Take
The running ancestor of grain sorghum: fast, drought-proof and legally noxious across much of the world, so grow it only where the law and a container both agree.
Related Reading
Readers interested in Sorghum Grass frequently explore these as well: