Question 1

Where does the forecast come from?

Accepted Answer

Open-Meteo, which aggregates NOAA GFS, NWS HRRR, and ECMWF models depending on region. It's the same data feed the National Weather Service uses for public forecasts. Your ZIP is looked up via zippopotam.us to get a lat/lng, then Open-Meteo returns daily min/max temperatures. 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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