Why do we break a coconut at temples and pūjās?

it symbolises breaking the hard shell of ego to offer the pure inner self to God.

The coconut (śrīphala, the “auspicious fruit”) is one of the most common offerings in Hindu worship. The usual explanation is symbolic: the hard outer shell is our ego, and breaking it before God reveals the white, pure kernel and the sweet water inside — our true self, offered in surrender. Its three “eyes” are sometimes compared to the three eyes of Śiva.

It is also a practical, pure offering: sealed by nature, untouched by human hands inside, and available everywhere. That is why it is broken at the start of new ventures — a new vehicle, a building, a film — to seek Gaṇeśa's blessing, and why a whole coconut sits atop the kalaśa in most pūjās. A neatly split coconut is taken as a happy sign, but an uneven break does not mean anything bad.

After offering, the coconut is shared as prasāda. Where breaking is not allowed or not practical, offering it whole is perfectly fine.

Source: common practice

Dharma Q&A — vratas, festivals & temples · Ask a Jyotishi your own question