Frost dates in Iran

Why frost dates vary across Iran

A national figure would be no use to anyone here. The growing season runs from 179 frost-free days at Karaj to 334 at Khorramshahr — a difference of 155 days, which is the difference between one tomato crop and none. That is why every date on this site is calculated for one place at a time.

Latitude does the rest. This list reaches from Bandar Abbas in the south to Ardabīl in the north, 11.1° of latitude apart. Distance from the sea matters too: coastal towns hold summer warmth into autumn and frost later, while an inland town at the same latitude can lose its season weeks earlier.

1 of the places here record no reliable air frost at all, so their rows read “none”. That does not mean nothing limits planting — heat, the wet season and day length take over as the constraint — and the crop pages say so where it applies.

How to read the table

Last frost is the median date of the final spring frost: in half of the years on record the last frost fell before it, in half after. First frost is the median date of the first autumn frost, and season is the number of frost-free days between them. All three are measured at the 0 °C air-temperature threshold.

A median is a planning date, not a guarantee. Plant tender crops on it and you accept roughly a one-in-two chance of a later frost in any given year. Each town page shows the cautious date — safe in nine years out of ten — alongside it, together with the earliest and latest frost the record holds. Read how the figures are calculated.