Use thousand grain weight to accurately calculate seed rates

Given that yields were much lower in 2026, Teagasc Crops Specialist, Shay Phelan urges growers to check thousand grain weights (TGW) before drilling this autumn.

Although many growers have been drilling crops over the last week or so, the vast majority of crops will be drilled over the coming weeks.

Anything planted up until now will have higher pressure from Barley Yellow Dwarf Virus (BYDV), grass weeds, disease and lodging, which will, in all likelihood, increase growing costs.

Soil conditions, despite the recent rainfall, are ideal and we can expect good establishment in these conditions and temperatures.

One area that is of a little bit of concern is the seed rate that growers use. General recommendations based on previous years seed rates have little bearing on the seed rate of the variety that you are about to drill in 2026. All seed rates should be based on the thousand grain weights (TGW) as this is the most accurate calculation of the weight of seed required. The calculation of the seed rate is as follows:

Seed rate (KG/ha) = TGW x desired plants/m²    e.g.        55 X 280    = 193 kg/ha (see bold below)

Establishment rate: 80%

The thousand grain weight will differ between varieties and even within batches of the same variety. Remember, the thousand grain weight printed on the recommended list is the three-year average and not the TGW for the current crop. Given that yields were much lower in 2026, it’s likely that the TGW of the seed for this autumn is likely to be different than what was used last year.

The tables below show the seed rate for winter barley, winter wheat and winter oats at different TGW for the different weeks, at the different seeds/m² and establishment rates.

Table 1: Seed rate for winter barley

Table 2: Seed rate for winter wheat

Table 3: Seed rate for winter oats