Growing

Planting & transplant dates

Work the whole schedule backward from your own last frost date — when to start indoors, when to set out, when it comes off.

Result

Your average last spring frost2027-04-20

CropTomato

Start seed indoors

Mar 9

6 weeks before last frost.

Set out / transplant

May 4

2 week(s) after last frost.

First harvest, roughly

Jul 18

75 days to maturity from setting out.

Hardening off begins

Apr 24

7–10 days of increasing outdoor exposure. Skipping this is how a flat of seedlings dies in an afternoon.

What this will not do

Plant by the soil probe, not by this calculator. These dates tell you when to be ready; 4-inch soil temperature tells you when to go. 45–50°F for potatoes and peas, 60°F for beans and squash.
Days-to-maturity on a seed packet is counted from transplant for started crops and from sowing for direct-sown ones, and it assumes good conditions. Add time for a cold spring.
A frost *date* is an average, which means it's wrong half the time by definition. The frost alarm is what actually saves the tomatoes.

The full build and the reasoning are in Chapters 16, 17, 19 of the guide.