Why can’t I turn on climate-adjusted days to maturity?

Hover the greyed-out Use climate-adjusted DTM switch: Heirloom tells you why in one line, so you know right away what to fix. There are four reasons:

• Your farm’s latitude and longitude are missing: add them in Settings, General.
• Heirloom cannot adjust this crop yet.
• The crop cannot reach maturity in your climate.
• The crop has no row in your Charts.

Once the switch is on, the days to maturity and the First harvest follow the field planting date. See Use climate-adjusted days to maturity in a planting.