What does the outside optimal growing period warning mean?

It tells you, before you sow, that this planting is set outside the weeks where the crop does well on your farm, so a risky date never slips by unnoticed. The message This planting is outside its optimal growing period shows under Use climate-adjusted DTM when the field planting date falls outside the crop’s Optimal Growing Period.

Read the first harvest date as the earliest you can hope for: out of season, the crop will likely take longer. Then choose: move the field planting date back into the good weeks, give the planting some protection such as a tunnel, or keep the date knowingly for an early or late crop you are ready to gamble on. See Understand the "Outside optimal period" warning.