Live Maize Heat Unit Service

Historic UK Heat Unit Map
Historic UK Heat Unit Map

KWS now provides a live ‘free to access’ service for all farmers and advisors, to assess maize heat units for their farm and region. The service is really easy to use;

  • Enter your postcode
  • Data shows the live heat units for your farm, compared to the long term average

Useful facts and recommendations:

A heat unit is calculated using formulae combining daily minimum and maximum temperatures, discounting mean values less than 10C, the minimum temperature suitable for maize growth

  • Heat units are updated weekly, between April to October
  • Approximately 120 heat units are needed for a maize plant to fully emerge
  • Approximately 45 heat units are needed to form a new true leaf
  • Heat units do not account for radiation (sunlight), field aspect (north or south facing), or reflect likely sowing date

Early varieties (FAO 150 – 160) require around 2,100 heat units by the middle of September to reach maturity. Later varieties (FAO 180 – 210) need around 2,400 heat units.

Later maturing energy maize hybrids, used exclusively for biogas (FAO 240 – 260) require between 2,500 – 2,800 heat units, depending on drilling date.

The above calculator is supplied by KWS UK Ltd and WeatherQuest UK Ltd. All reasonable steps have been taken to accurately reflect real time temperature data, and this tool is intended as a guide during the growing season. It is not designed to determine sowing date. No liability is accepted whatsoever arising from actual crop performance based on this calculator.

Maize Heat Unit Calculator

Select your recommended variety based on your 10 year average