However you sow winter beans think hard about what you are trying to achieve, and be sure to take seed size into account, growers are being urged.

The crop can produce good yields from plant counts lower than many people realise, says the PGRO’s Geoffrey Gent.

Trials and grower experience shows that thin stands with as few as 12 plants/sq m can give satisfactory results.

But despite the optimum winter population for most conditions being 18/sq m, growers often end up with more.

That is because they do not adjust rates enough for changes in thousand grain weight (TGW), says Mr Gent.

Dense crops may seem satisfactory in early spring, but can grow too tall, lodge and suffer irregular pod set.

However, overall this autumn’s seed is bigger than normal, which could help.

It could leave potentially over-thick stands closer to the optimum.

“Seed from the 2005 harvest is generally larger than usual, so unless an allowance has been made for this, populations could be reduced,” he says.

Normally, Clipper and Target have TGWs of 600-700g and Wizard 700-750g, says Peter Smith of Lincs-based winter bean specialist Wherry & Sons.

“We’re seeing an enormous variation in seed size this year.

It ranges from 750 to 900g.”

So at the typical 16 seeds/sq m rate for early sowing on light land growers might need to sow as little as 115kg/ha or as much as 140kg/ha.

“For later sowings on heavier soils, say at 24 seeds/sq m, you could need anything from 173 to 211kg/ha depending on TGW.

That’s nearly double the lowest that might be enough earlier.”

Growers relying on ploughing down surface-spread seed can justify 5% higher seed rates than for drilling, he advises.

At least half the crop is still established by ploughing down, but plenty of alternatives are being explored to improve returns, notes Mr Gent.

Trials over many years show that plant density is the over-riding factor determining final output.

“An awful lot of effort goes into deciding seed rates for winter wheat and other crops, and winter beans could benefit from similar attention.

“The key thing to remember is that the crop usually grows vigorously, can tiller profusely, especially at low densities, and can withstand and compensate for a lot of damage from birds and frost.”

andrew.blake@rbi.co.uk