Blackbirds rear 2-3 broods. In a good year, fourth broods may be attempted. Weather determines the timing of the breeding season.

Warm or cold spells in spring can bring the breeding season forward or delay it by several days. Dry weather in June can shorten the season and even cause starvation of late broods. The nesting season starts up to two weeks earlier in gardens than in woodland.

The nest, built by the female, is low down in any suitable cover. Trees, shrubs and climbers are preferred, but nests can be found inside buildings, occasionally even on the ground.

The nest is a substantial cup of grass, straw, small twigs and other plant material. It is plastered inside with mud and lined with fine grass. It can take two weeks to complete, and sometimes the same nest is used for successive broods.