Holy smokes, my carrot seeds just emerged faster than they ever have: nine days! Most sources say that carrots take between one and three weeks to germinate, and I’ve often found my carrot seeds emerging from the dirt more on the three-weeks end. Why so fast this time?
I believe it was the soil temperature. As this page from Cornell says, the ideal soil temperature for carrot germination is 75 degrees. While I haven’t measured the temperature of my soil, I can see that the temperature of the soil at a nearby CIMIS station averaged 76 degrees in September and 69 degrees in October, likely putting the soil temperature when I sowed my carrots on October 19th close to that ideal of 75 degrees.
What does this mean? Optimal carrot-sowing season is mid-September through mid-October — for my yard, and probably throughout Southern California. That’s when the soil temperature is likely near 75 degrees. (See the CIMIS site location map for a station near you.)
Carrots will certainly germinate in soil with temperatures above and below 75 degrees but more slowly. The most discouraging thing about growing carrots for me has always been that I have a hard time remembering to keep the seed bed moist for a whole 21 days. Staying on top of watering for only a week? I can manage that.
Cornell also says that carrot roots develop their best quality when they grow in soil with a temperature of 60 to 70 degrees. That’s what mine will be growing in through November here.
The point is, sow carrots today! It’s not too late, as the soil temperature is still pretty warm. Or, put it on the calendar to sow carrots between mid-September and mid-October, 2017. I just did.