Seed potatoes are classified according to the length of time they take to mature, but this can be influenced by weather. Maincrop seed potatoes mature in 125-140 days and, if planted in late April, can be harvested by mid August, sometimes continuing through to October. Maincrop seed potatoes can be planted from mid March onwards as a rough guide, dependent on weather.

Maincrop potatoes are higher yielding than first earlies and second earlies, and usually have larger tubers.

Maincrop cultivars can either be used fresh from the ground or stored for winter use.