Seed stocks which may emerge irregularly or have incomplete emergence in the field can be identified by using a germination test. Dormancy in potatoes is controlled by internal cues as well as environmental cues (endodormancy and ecodormancy). Tuber age is an important factor; for example, samples received in December may begin germinating at a similar time to those received in September even though they have been in the germination cabinet for a much shorter period of time. From 2021, NIAB will begin germination testing in November; samples sent earlier will be held until this time, but we would recommend that samples are stored.

NIAB recommend a sample size of 100 tubers for germination testing. The germination test is carried out by placing the sample of seed tubers in a controlled temperature cabinet kept at 15 °C. A tuber is said to have germinated when it has produced a sprout of 3 mm in length or greater. Sprouting is recorded weekly until 100% germination is achieved or four weeks have elapsed since the latest sprout <3 mm was produced. The final number of germinated tubers, and the date of 50 % and 100 % germination are reported and compared to benchmarks, both within and between seasons.