Sorghum: growing in the garden, harvesting the grain and uses

In brief: Sorghum (Sorghum bicolor) is a heat-loving annual grass related to maize. Sow it only in the second half of May into soil warmed to 12–15 °C, 3–5 cm deep. It tolerates drought and the grain is gluten-free, but young and frost-damaged plants contain a substance that releases hydrogen cyanide, so do not feed them to animals.

In the Czech Republic sorghum is more of a field crop, but it finds a place in the garden more readily than you might expect. Tall clumps with panicles full of colourful grains look like an ornamental grass, the grain can be milled into gluten-free flour, and broomcorn sorghum is the raw material for traditional brooms. Thanks to its deep roots it also copes with dry summers, when maize wilts.

It has two pitfalls, however: it does not tolerate cold soil, and as animal feed it can be dangerous at certain stages. Below you will find how to sow and grow sorghum, when to harvest, what to do with the grain and what to watch out for.

Types of sorghum: grain, sweet, broomcorn

All garden and field sorghums belong to one species, but they differ in height and purpose. The seed packet should say which type it is.

The first Czech variety of grain sorghum is Ruzrok from the Crop Research Institute, registered in 2014. It was bred precisely so that it can ripen in our conditions.

Where and when to sow sorghum

Sorghum is a C4 plant like maize and millet: in warmth and sun it grows quickly and uses water more efficiently than cereals. According to the Crop Research Institute's methodology, it uses up to a third less water per season than maize, and its roots reach down to a depth of 150 cm. In the cold, on the other hand, it stands still.

1. Site: full sun, warm and sheltered. Tall types cast shade, so put them on the north side of the bed.
2. Soil: medium-heavy, deeper and rich. It also tolerates lighter and drier soil, but not waterlogging. Work in compost before sowing.
3. Timing: only in the second half of May, after the last frosts. The soil must be at least 12–15 °C; in cold soil the seeds rot.
4. Sowing: 3–5 cm deep. In the garden sow in rows 40–60 cm apart, with seeds 5–10 cm apart in the row, and thin to 15–20 cm after emergence.
5. Emergence: in 10–14 days. In cold weather, covering with white horticultural fleece helps.
6. First weeks: for 4–5 weeks after emergence sorghum grows slowly and weeds easily outgrow it. Until then, weed and hoe the bed.

If you grow maize in your garden, sorghum is grown in a very similar way; a comparison can be found in the article on maize.

Care during the summer

• Watering: water young plants in dry weather. Once they have rooted, they cope even with longer drought. They need the most water when they are elongating their stalks and forming panicles.
• Feeding: sorghum is demanding in nitrogen and potassium, and takes up the most nutrients in July and August. Compost before sowing and one feed at the start of summer are usually enough.
• Weeds: once the stand closes up, it keeps weeds down on its own.
• Support: earth up tall sweet and broomcorn types in a windy spot, or tie them up.

Diseases are still rare here; in a wet year leaf spots may appear. On the stalks the European corn borer may do damage, just as on maize.

Harvest and uses of the grain

Grain sorghum ripens from September to October. Harvest the panicles when the grains are hard, glossy, fully coloured and cannot be dented with a fingernail. Cut them off with a piece of stalk and leave them to dry hung up in a dry, airy place. Dry grains can be rubbed out against a sieve or threshed in a sack.

Birds love sorghum and can peck a panicle clean within a few days. Protect it with netting from the start of ripening, or wrap the panicles in bags of fleece or tulle.

How to use the grain

• Porridge and side dish: cook the whole grain like pearl barley or buckwheat. Soak it beforehand.
• Flour: sorghum flour is gluten-free. It is not suitable for baking on its own and is added to mixes.
• Tannins: dark grains have tannins in the husk with an astringent taste. Industrially the husk is abraded off; at home, soak the grain and pour the water away.
• For birds: panicles hung up on a feeder in winter will be appreciated by tits and sparrows. More in the article bird feeders and helping animals in the garden.
• Decoration: dried panicles of broomcorn and ornamental sorghum last for years; how to work with grasses in the garden is shown in the article ornamental grasses – an adornment of the modern garden.

Beware of hydrogen cyanide: sorghum as fodder

Young sorghum plants contain the cyanogenic glycoside dhurrin. When the tissues are damaged, for example by grazing, trampling or frost, hydrogen cyanide is released from it. For a person eating cooked ripe grain this is not a risk. For animals, however, the green material can be dangerous.

• Do not feed young sorghum and do not let cattle, sheep or goats graze it. The University of Wisconsin extension service recommends waiting until the plants are at least 50 cm tall.
• After a frost that damages the plants, wait at least a week before feeding.
• Plants stunted by drought have a higher content.
• Hay and silage from mature plants are safer, because the hydrogen cyanide is released during drying and fermentation.
• Give rabbits and poultry only ripe dry grain, not green leaves.

Sorghum as a sanitising catch crop

The same property also has a useful side. According to the Crop Research Institute, sorghum incorporated into the soil is used as a phytosanitary catch crop: during the decomposition of dhurrin, the released hydrogen cyanide limits nematodes and soil fungal pathogens. It is used mainly before vegetables, garlic or potatoes. More about nematodes in the article pests – root nematodes.

Common mistakes when growing sorghum

• Sowing into cold soil: seeds sown in April or early May rot or emerge sparsely.
• Neglected weeding: it grows slowly in the first month and weeds get ahead of it.
• Tall variety in shade: sweet and broomcorn sorghum need the warmest spot, otherwise the grain does not ripen.
• Unprotected panicles: without netting, the birds harvest before you do.
• Green leaves for animals: do not feed young or frosted plants.

Frequently asked questions

When should sorghum be sown?

In the second half of May, once the soil has warmed to at least 12–15 °C and there is no risk of ground frosts. Earlier sowing does not pay off.

Is sorghum gluten-free?

Yes, sorghum grain contains no gluten, which is why its flour is suitable for gluten-free cooking. With shop-bought products, check that they are not contaminated with other cereals.

Is sorghum poisonous?

Not the ripe cooked grain. Young green plants and plants damaged by frost, however, contain dhurrin, from which hydrogen cyanide is released, and can be dangerous for cattle, sheep and goats.

Does sorghum ripen in the Czech Republic?

Grain varieties do, especially in warmer regions; they need 120–140 frost-free days. Tall sweet and broomcorn types ripen only in a warm year.

What is sorghum used for?

The grain for porridge and gluten-free flour, sweet sorghum for syrup, broomcorn for brooms, and whole plants as fodder, biomass or a sanitising catch crop. In the garden also as an ornamental grass and food for birds.

Recommended products

We do not currently stock sorghum seed. The following are useful when growing it:

• Bird protection net 5 × 5 m – protects ripening panicles from being pecked.
• Fleece 1.6 × 5 m for early harvests, white – warms the soil after sowing and protects emerging plants on cold nights.

Sources

• Cultivation technology of grain sorghum variety Ruzrok (Crop Research Institute, 2018)
• Prussic acid and nitrate toxicity in sorghums (University of Wisconsin–Madison, Division of Extension)
• Growing and using sorghums (Agromanuál)

Updated: 27 September 2026