LG Heatmap Tool

We've developed the LG Heat Map Tool in conjunction with The Met Office to provide quick and easy advice for maize growers on variety selection.

To find out which maize varieties may be suitable for your farm, simply enter your postcode below to discover the number of heat units available to grow maize in your area.

Your Results

The LG Heat Map Tool uses the internationally recognised Ontario Heat Unit (OHU) system to show the average available heat units, calculated from a 10 year period, available for maize to be grown in a particular location.

Your 10 Year OHU Average
0 units
Recommended Varieties
All reasonable steps have been taken to accurately reflect temperature data by area. This tool is intended as a guide for appropriate maturity selection of maize varieties. Factors such as site, exposure and sowing date also need to be taken into consideration. No liability is accepted whatsoever arising from actual crop performance from varieties selected using this tool.

In the UK maize needs a minimum of 2,500 Ontario Heat Units (OHU’s) to accumulate over the growing period to mature. In simple terms, if there are too few heat units then the crop will struggle to mature.

Maize varieties differ in the number of heat units required and this affects their suitability to be grown in different locations. 

As a guide:

  • Very early varieties: - FAO 140-180 (MC 12-9) require 2,500 – 2,750 OHU’s to mature
  • Early varieties: – FAO 180-200 (MC 9-7) require between 2,750 -2,900 OHU’s to mature
  • Later varieties: – FAO 200-230 (MC 7-4) require 2,900+ OHU’s to mature

Typically, the blue areas on our OHU map are unsuitable for growing maize in the open as the number of OHU’s are below the minimum 2,500 units required. The red areas have plenty of heat units available and marginal areas are shown in the bordering lighter colours.

OHU’s are calculated for the maize growing period from mid -April to mid- October combining maximum daytime temperatures above 10°C and night time minimum temperatures below 4.4°C (above which maize actively grows).

The LG Heat Map Tool does not take into account the amount of radiation (sunlight), field aspect (north or south facing), or site exposure (e.g. windy or sheltered) into account. If your field is not south facing and/ or is sited in an exposed spot, then you should consider choosing varieties with a lower OHU score than your average as they require less heat units to reach maturity.

The tool also does not reflect sowing date. Maize should only be sown once soil temperatures have consistently reached 8-10°C over a 5 day period.

Whilst every care is taken to produce reliable and accurate guidelines, no liability can be accepted for any use made of this information. It is always advisable to consult your local agronomist and consider your own experience.