Question 1

Where does the forecast come from?

Accepted Answer

The National Weather Service (api.weather.gov), the same forecast weather.gov shows for your location. Your ZIP is looked up via zippopotam.us to get a lat/lng, then the NWS point forecast gives the daily low and high for the next few days. No signup, no API key, no logging.

Question 2

At what temperature should I cover my tomatoes?

Accepted Answer

Any time the forecast low drops to 33°F or below. Tomatoes are damaged at the first hint of frost and killed outright below 30°F. Covering works best with a frost blanket or even a bedsheet draped over a cage. Anything that traps radiant ground heat works. Remove the cover by 9 AM so the plants don't cook under trapped solar heat.

Question 3

Why are kale and spinach in the 'fine' list even at 20°F?

Accepted Answer

Both are very-hardy and their flavor actually improves after light frost. Cellular sugars concentrate as the plant protects against freezing. You can leave kale uncovered through 15-20°F events without damage, and it's one of the reasons it's the classic fall-to-winter extender.

Question 4

How much does covering actually help?

Accepted Answer

A single layer of frost blanket adds about 4-6°F of protection. A bedsheet adds 2-4°F. Rigid row cover over hoops adds 5-8°F. The reason covers work isn't insulation per se. It's preventing the plants from radiating their own heat to the clear night sky. Clear calm nights lose 4-6°F of radiative heat overnight, and covering that sky view keeps most of that heat in.

Question 5

Should I water before a frost?

Accepted Answer

Yes, counterintuitively. Water has a huge heat capacity, so wet soil releases heat overnight much more slowly than dry soil. Water deeply in the morning of a frost day. For commercial crops, sprinkling water on the plants overnight works because the phase change of freezing water actually releases 144 BTU per pound of heat, but that's a lot of water and equipment and isn't practical for most gardens.

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