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  • Writer's picturePhilip

Black-grass – Facts Table

The discussion around Blackgrass never really stops. There are numerous scientific papers which I have referenced over the years such as Morse & Palmer 1925, Warrington 1936, Thurston 1972 and Moss 1983. All confer data upon this weeds biology and control. More recent papers (February 2023) have appeared from places such as the Warsaw University of Life Sciences in Poland and although interesting often only affirm what is already understood.

For a more enjoyable experience surrounding the exploits of farmers and Black-grass there are countless colour advertorials found in the Agricultural Comics expounding the virtues of this and that. Recently whilst taking a poll upon “what’s new” for autumn 2023 I came across a Black-grass “Facts Table.” Although a good summary table on the subject of Black-grass I did think it could be expanded upon a little. I hope the expanded version assists with your decision making processes regarding this troublesome weed.

Original Table (Black Ink.)

Number of seeds produced per plant: Up to 1000 per plant.

Revive Agronomy

Seed numbers range from 80 to 124 per spike (stalk with ear.)

Around 85% of the seed is produced by the primary tiller and viability of produced seed ranges from 49 to 77%.

Seed shed: June to August

Revive Agronomy

As many as 50% of the spikelet’s lack viable seed.

Since 70% of seed sheds mid-July to mid-August, it is estimated that 180 to 300 million seeds per hectare are harvested in Barley.

In winter wheat over 95% of the Black-grass seed is shed before harvest so overall contamination within the harvested crop is low.

Germination depth: Up to 5cm

Revive Agronomy

Between 85 – 90% of seed germinates in the top 40 mm of soil. Seed “sown” below 150 mm often fails to grow at all – that year.

Primary dormancy: Varies with summer temperatures, hot = low dormancy, cold = high dormancy.

Revive Agronomy

Fresh seed has a 4 to 6 week “after ripening period.” Less primary dormancy occurs in seed harvested later in the season. Studies show that 65% of newly emerging Black-grass plants arise from recently shed seed.

Does it have a secondary dormancy? Yes

Revive Agronomy

Around 10 to 20% of seed have an extended dormancy, which is, in part, broken by alternating temperatures. Dormancy is enforced by waterlogged soil.

Seed longevity: 1 - 5 years

Revive Agronomy

Around 80% of the seed within the soil is “lost” within 12 months although some seed will remain viable for up to a further 4 years.

Factor promoting germination: (Light)

Revive Agronomy

Germination can vary greatly between individual populations and is seasonally influenced. Burying seed can induce dormancy whereas exposure to “red light” promotes germination.

Soil Type: Thrives on a wide range of soil types, predominantly water retentive heavy clays or silts, but very adaptable.

Revive Agronomy

A crop which has received an optimal fertiliser policy will produce 3 times as much Black-grass biomass as one that receives zero fertiliser.

Seed from unfertilised plants has a germination rate of 70% and those from a fertiliser plant 50%


A Spike is a group of flowers arising from the main stem, without individual flower stalks (sessile).


A spikelet consists of one or more flowers (florets) plus two basal membranes (glumes). The spikelet is attached to an un-branched axis called the rachilla.


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