Kerman sits at an altitude of 1,750 metres, which means its climate is more forgiving than the surrounding desert lowlands. Even so, summer (June–August) is fiercely hot — afternoons regularly above 35°C — and a trip into the Lut Desert is genuinely dangerous in this period.
Spring (March–May) and autumn (September–November) are the best times: pleasant warm days, cold clear nights, the gardens in good condition, and the Lut just about manageable in the early morning or late afternoon. The Persian New Year (Nowruz, around 21 March) brings domestic crowds and many places close for a few days.
Winter (December–February) is cold — sometimes well below zero at night, snow on the surrounding mountains — but the days are clear and the desert is at its most photogenic. Bring layers; many cheaper hotels have only modest heating.