Sowing winter wheat late: Understanding the risks

Jason Pole provides an overview of sowing-date information in the winter wheat recommended list and highlights the risks associated with very late sowings.

In the Recommended Lists for cereals and oilseeds (RL) trials, winter wheat is sown over a wide range of dates to reveal the impact on variety performance.

I will provide an overview of the main winter wheat drilling periods and summarise an Agronomy Conference 2025 presentation (by Paul Gosling) that looked at vernalisation risks.

Most winter wheat trials are sown between 25 September to 1 November. However, others stretch the drilling window to provide data for the three rows in the ‘sowing date’ section of the RL winter wheat tables.

This row uses yield data from a dedicated series of trials that are sown very early (25 August to 14 September). It also uses yield data from sites drilled before 25 September in the main trial series.

The late-sown trials (drilled from 1 November to 31 January) help us determine the potential extent of any yield penalty in varieties drilled after October.

Following a difficult drilling period for the harvest 2024 crop, we ran an analysis that showed winter wheat varieties often produce respectable yields when sown late, even when drilled into January.

This is especially true for those varieties that have latest safe-sowing dates that run into February.

To provide latest safe-sowing date information, we sow vernalisation trials, where winter wheat is drilled very late.

Historically, we have used three drilling dates:

• 10 March
• 24 March
• 7 April

However, we recently added a February drilling date (from 2024 onwards).

Unlike the other sowing windows, these trials focus on crop development and do not generate yield data.

Vernalisation is based on complex low-temperature and day-length interactions that advance crop development.

As this includes reproductive development, yield can be compromised if the crop is not exposed to sufficiently cool periods.

Usually, vernalisation occurs when temperatures are below 8°C, taking about four to eight weeks.

When sown in the autumn, all winter wheat varieties will sufficiently vernalise.

The current cold snap will help.

As sowing dates move later into winter, the risk of insufficient vernalisation increases – with the risk highly dependent on the variety.

The vernalisation trials are in the RL East region (Essex) and include all winter wheat recommended and candidate varieties.

We also include a spring wheat variety as a control (which has a relatively low vernalisation requirement).

RL trial operators assess all variety plots at two growth stages (with timings and assessments based on the spring wheat control).

Ear development at growth stage 61 (start of flowering – first anthers visible)

Heading score 1–9:

• 1 = no ears (still vegetative growth)
• 9 = 100% ear development

Maturity at growth stage 91 (start of ripening – grain hard/difficult to divide)

Ear-maturity score 1–9:

• 1 = ears green
• 9 = ears fully ripe

The results are used to set the three latest safe-sowing date categories:

• End Jan (29)
• Mid Feb (3)
• End Feb (2)

The bracketed figures indicate the number of varieties currently allocated to each category, although some of the allocations are based on limited data (see RL 2026/27 for information).

We err on the side of caution and use conservative estimates when setting the dates.

As a result, it may be safe to drill later depending on where you farm (but get advice from the breeder or agent of the variety before you do this).

Figure 1 illustrates how risk is affected by the variety, the drilling date and the year.

The charts show significant reductions in heading scores at an early April drilling date, compared to a mid-March drilling date.

Varieties with the latest (end-of-February) safe-sowing dates hold up best.

The 2025 trials produced unusual heading scores, which followed a relatively warm March and April.

At the mid-March drill date, heading scores were relatively low, with only Skyfall performing well (the only variety in this chart with an end-of-February latest safe-sowing date).

When drilled later (in the early April slot), no varieties vernalised in 2025.

Assuming all else remains equal (e.g. similar genetics), sowing winter wheat very late is likely to become riskier.

According to climate change predictions, all areas of the UK are likely to get warmer.

Last year (2025) was (provisionally) the UK's warmest (and sunniest) year on record.

Although the amount of warming is expected to be more extreme in the summer, other seasons are highly likely to be warmer too.

Even in a low-emission scenario, UK winters may be up to 2°C warmer for the 2060 to 2079 period (compared to a 1981 to 2000 baseline). Certainly, cooling is unlikely.

Plant breeding will adapt to these changes and so will the RL.

We used to have RL trials where spring wheat was drilled in the autumn and we may need to look at this again, should vernalisation become more of an issue.

Figure 1a. Winter wheat variety heading scores from RL vernalisation trials (mid-March drilled)

Figure 1b. Winter wheat variety heading scores from RL vernalisation trials (early-April drilled)

Figures 1a and 1b: Heading scores from dedicated RL vernalisation trials over several years for varieties either drilled in mid-March or early April.

Trial data is not available for all years due to the challenges of consistently drilling in March. RGT Bairstow and Gleam are no longer listed on RL 2026/27. LG Skyscraper, which was a control variety, is also no longer listed.