Great Millet

About

Sorghum is the fifth cereal by world production, behind maize, wheat, rice and barley, and it is the one that grows where the others fail. It handles heat, drought, poor soil and periodic flooding, and when conditions turn against it, it stops growing and waits rather than dying. That ability to pause and resume is what makes it the staple across the African Sahel and the Indian Deccan.

The plant is a C4 grass, using the same efficient photosynthesis that maize and sugar cane do, and it looks like a coarse maize with a head instead of a cob. Its root system is twice as extensive as maize’s and its leaves carry a waxy bloom that cuts water loss.

One species covers several crops. Grain sorghum is grown for the seed. Sweet sorghum has a juicy stem that is crushed for syrup. Broom corn is the type with long stiff panicle branches, and it made brooms for two centuries. Forage types are grown for animal feed, and they are the ones most involved in cyanide poisoning.

Appearance and character

Sorghum looks like maize until you reach the top. The stems are stout and solid, the leaves are long, broad and blue-green with a distinct white midrib, and the plant stands anywhere from a metre in modern grain varieties to four metres in traditional African ones.

The head is a panicle rather than a cob, dense and upright in grain types and loose and spreading in broom corn. It carries hundreds of grains, and depending on the variety they ripen white, cream, yellow, red or a deep brown.

Where maize carries its male flowers in a separate tassel and its female flowers on a cob, sorghum has ordinary perfect flowers in the panicle and pollinates itself. That is the quickest way to be certain which plant you are looking at.

Where it is from

Sorghum was domesticated in north-eastern Africa, in the region of modern Sudan and Ethiopia, from wild Sorghum bicolor subspecies verticilliflorum. The archaeological evidence points to somewhere around 4000 to 3000 BC, and the domestication was slow and multi-centred.

From Africa it moved east along trade routes into India by around 2000 BC, and into China. Indian sorghum, jowar, became a staple of the Deccan plateau and remains so. The crop reached the Americas in the transatlantic slave trade and became a major feed grain in the United States.

Africa retains the greatest diversity, with distinct races developed for different climates and uses. Durra belongs to the dry Sahel, guinea to the wetter west, kafir to southern Africa and caudatum to the centre. That diversity is the reason sorghum can be adapted to conditions from the Sahara’s edge to the Ethiopian highlands.

How it grows

Sorghum germinates in warm soil and grows slowly for the first month, putting its energy into roots. Once the root system is established it accelerates and can put on several centimetres a day in warmth.

Many traditional varieties are short-day plants that will not flower until the nights lengthen, which is why an African variety grown in Britain may grow all summer and never produce a head. Varieties bred for temperate agriculture are day-neutral and flower on a schedule.

The panicle emerges from the top of the stem, flowers over about a week from the top downward, and fills over five to six weeks. The plant will regrow from the base after cutting, and that regrowth is the highest-cyanide tissue it produces.

Through the seasons

In Britain, sow under cover in April and plant out at the end of May, or sow directly in late May once the soil is reliably above 15 deg C. Cold soil gives poor patchy germination.

Growth is slow through June and rapid through July and August. A day-neutral grain variety should head in August and start filling immediately.

Harvest in September or early October, cutting the heads once the grain is hard and the panicle has coloured. The first frost ends the plant, so a late season is a race. Dry the heads under cover and rub the grain out.

Care difficulty

Sorghum is easy to grow and hard to ripen in Britain. The plant itself asks for almost nothing once it is up, tolerating drought, poor soil and neglect better than any other cereal you could sow beside it.

Heat is the constraint. It needs soil above 15 deg C to germinate properly and sustained warmth to fill grain, so a cool British summer produces a handsome plant with an unfilled head. A sheltered sunny wall or a polytunnel changes the odds considerably.

Choose the variety with the season in mind. A day-neutral early grain variety sold for temperate growing will head in August. An ornamental or African landrace may be a short-day type that never flowers here at all.

Watering

Water at sowing and through the first month while the roots establish. After that, sorghum needs very little. Faced with drought it rolls its leaves, shuts down and waits, then starts again when water returns.

A deep soak in a long dry spell is better than frequent light watering, since the roots go down and shallow watering keeps them near the surface.

Do not water a crop that has stopped growing in a drought. The plant is doing what it evolved to do, and it will start again. Watering a drought-stressed crop and then leaving it can also produce a flush of high-cyanide regrowth.

Warning signs, diseases and pests

Birds cause more sorghum loss worldwide than anything else, and the red-billed quelea is the most destructive bird in agriculture anywhere. On a British plot it is pigeons and finches, and a ripening head needs netting.

Aphids gather on the undersides of leaves and on the head, and the sugarcane aphid has become a serious sorghum pest in warm climates. Look for sticky honeydew and sooty mould on the leaves below a colony.

Leaf blights and anthracnose show as elongated purple or red lesions on the leaves in humid weather. Sorghum’s own pigments make the symptoms colourful and easy to see, and a garden crop rarely suffers enough to matter.

Smut replaces individual grains with sooty black masses in the head, and any affected head should be cut and burned rather than composted. Slugs take young plants in a cool wet start, which in Britain is the commonest early setback.

Growing environment

Full sun, and as much heat as the site can supply. A south-facing wall, a raised bed that warms early, or a polytunnel all improve the chance of a filled head.

Soil tolerance is very broad. Sorghum grows on heavy clay, on sand, on alkaline soil to pH 8.5, and on ground with a salinity that would stop maize. It also tolerates short periods of waterlogging better than most cereals.

Temperature sets the limits. The crop stalls below 15 deg C, is damaged at 5, and is killed by frost. In Britain that means the growing season runs from the end of May to the end of September, which is exactly long enough for an early variety and not enough for anything else.

Feeding

Sorghum is a bulky plant and takes a reasonable amount of nitrogen, though less than maize does for the same growth. One dressing of a balanced granular feed at around six weeks covers a garden crop.

Stop feeding once the head has emerged. Late nitrogen delays maturity, which is the wrong direction in a British season, and produces soft growth that lodges.

Nitrogen and stress interact in a way worth knowing. A crop given plenty of nitrogen and then hit by drought accumulates nitrate in the stems as well as cyanogenic glycoside in the leaves, which is why forage sorghum has feeding rules attached to it.

Troubleshooting

Is sorghum gluten-free? Yes. It contains no gluten and is used as a gluten-free flour, particularly in the United States and across west Africa.

Can I grow it in Britain? You can grow the plant easily. Filling a head takes a warm summer and an early day-neutral variety, and a polytunnel or a sunny wall improves the odds a great deal.

My sorghum never produced a head. Most likely a short-day variety, which will not flower until nights lengthen past a threshold that Britain reaches too late in the year. Buy an early grain variety bred for temperate growing.

Is sorghum poisonous? The mature grain is not. The green plant contains dhurrin, which releases cyanide when the tissue is damaged, and concentrations are highest in young shoots, in regrowth after cutting, and in drought-stressed or frosted plants. Keep livestock off it in those conditions.

What is sweet sorghum? A type grown for the juice in its stems rather than for grain. The canes are crushed and the juice boiled down into a dark syrup, which was a common sweetener in the American South before cheap cane sugar.

What is broom corn? A sorghum type with long stiff branches in the panicle, grown to be made into brooms. It is the same species and it makes poor eating.

How do I use the grain? Whole, boiled like rice for about 50 minutes; milled into flour for flatbreads and porridge; or popped in a dry pan like popcorn, which works and produces something much smaller.

How is it different from maize? Sorghum carries perfect flowers in a panicle at the top of the stem and pollinates itself. Maize carries a male tassel at the top and female cobs at the leaf joints. The leaves look similar and the heads settle it.