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HomeFarming NewsWhat influences grass growth on farms?
Catherina Cunnane
Catherina Cunnane
Catherina Cunnane hails from a sixth-generation drystock and specialised pedigree suckler enterprise in Co. Mayo. She currently holds the positions of editor and general manager at That's Farming, having joined the firm during its start-up phase in 2015.
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What influences grass growth on farms?

According to Patricia Lynch, drystock advisor, Teagasc Westport, a range of factors influence the amount of grass that grows on your farm.

These include:
  • Soil temperature;
  • Altitude and aspect;
  • Light and water;
  • Lime and fertilisers;
  • Grass-type;
  • Grazing management.

Grass growth on farms:

Soil temperature

Grass growth picks up significantly when soil temperatures at 10cm depth reaches above 5°C. There is a variation between grasses, e.g. Timothy may start growing at lower temperatures, while white clovers and other legumes begin at around 8°C.

Lynch highlighted that the plant becomes active at these temperatures and absorbs more soil moisture, which increases the uptake of nutrients and rate of growth.

She said that measuring soil temperature using a cheap soil thermometer is a quick, easy and cheap method of identifying when the plant is growing, so farmers can apply nitrogen (N) fertilisers to promote growth.

Altitude and aspect

Air temperature drops 1°C in every 100m rise above sea level, impacting grass growth, particularly the length of the growing season. North-facing pastures take longer to warm up in spring than south-facing ones.

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Light & water

All plants need light to drive photosynthesis reactions, which provides the energy for growth. The more light a plant receives, the more it can grow.

Too little water, she added, means grass leaves wilt, which means they cannot maintain an optimum light capture position. On the other hand, with too much water, a plant will slow or even shut down root activity.

Lime and fertilisers

Once the soil’s pH has been corrected, fertiliser nutrients are usually the most limiting factors to grow grass. “Nitrogen (N) governs yield; the faster the leaf grows, the more light it can intercept.”

“In young leafy swards, N can increase yield and density. In grazing systems, N is most effective at sward heights of between 4-8cm.”

She noted that phosphate (P) is essential for root and stem growth. Besides, Potassium (K) is essential for vital growth processes in the plant.


The Teagasc advisor outlined that different grass species and varieties have different characteristics, both in terms of yield and heading date.

She said farmers can choose varieties to suit their farming system based on information on yield, heading dates, feed quality etc.

Grazing management

According to Lynch, grazing grass at the ideal two-and-a-half-to-three-leaf stage increases grass growth and sward yield by maintaining the optimum leaf area to capture sunlight, which provides the energy for growth.

“It is important to remember that you need grass to grow grass as grazing too low of covers can significantly reduce grass growth.”

“As grass is the cheapest feed available to Irish farmers, target to make maximum use of grazed grass on your farm during the 2021 grazing season.”

Further reading:

You can find more farming tips and advice here.

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