Sixteen experiments over six seasons (1981–87) compared the growth and yield of up to 16 seed-tuber weights, ranging from 1–5 to 110–120 g, in one second-early and four maincrop varieties. Four of the experiments (1986–87) examined effects in seed tubers from seed crops planted in July; the remaining experiments used seed from crops planted at the normal time, April–May. Effects were similar for seed from the different planting dates. Plants from seed < 5 g (and occasionally up to 15 g) emerged slightly later and produced a smaller crop canopy that those from larger seed. The later emergence from the smallest seed was a consequence of a slower rate of sprout elongation. There were no effects of seed weight above 15 g on stem emergence or growth of the canopy. In 1982, a severe frost completely defoliated all plants in four experiments but within 2 weeks complete plant emergence was re-achieved from all seed weights except the smallest (1–5 g). The results suggest few differences between seed weights > 5 or 10 g in emergence from similar depths of planting or in recovery from frost damage.

Tuber yields were little affected by seed weight > 5 or 10 g, even at constant within-row spacings. Consequently, seed rates from 0·59 to 5·4 t/ha produced similar yields and the results suggest considerable economic benefits and potential for using seed tubers of much smaller weight than may be sold under current legislation. The use of small seed tubers from late-planted crops may result in further economies in production costs and reduction in disease in seed tubers.