Delaware gardeners can sow the hardiest unusual roots in early spring, but the frost date is only a starting line.

In Connecticut, the calendar date matters less than the soil temperature, and these roots wait for warm soil, not a frost-free forecast.

In the Denver area, the last spring freeze falls between May 1 and May 11, and the first fall freeze between September 30 and October 12.

Coastal and southern California has no frost date to wait for: Los Angeles records no freeze in an average year.

On the B.C. coast, the average last spring frost at the Vancouver International Airport station falls on March 18, which is early by Canadian standards.

Wait for warm soil, not just the last frost. At Little Rock’s NOAA reference station, the last 32°F freeze falls between March 12 and March 28, and the…

In Arizona, elevation matters more than any calendar date. In the Phoenix low desert, frost almost never sets the schedule.

Plan on sowing the hardy roots in the weeks after May 21 and treat the rest of the group as a bet against the calendar.

Anchorage’s last spring freeze falls between May 3 and May 12, and unusual roots such as celeriac, kohlrabi, horseradish and Jerusalem artichokes go in…

In most of Alabama, unusual root crops go in from late March into early April, but the soil sets the real date, not the calendar.