What does your greenhouse actually protect?
Record paired overnight minimum readings from inside and outside. See the measured difference across nights instead of assuming that an unheated greenhouse is frost-free.
No readings have been invented. Add dates and matching overnight minima from your own instruments.
Readings save automatically in this browser only. No account or server upload. Reset min/max thermometers for the same observation period; the paired minima can occur at different times.
How this works, and what it leaves out
This plots the readings you enter and subtracts the outdoor minimum from the indoor minimum for each night. A positive difference describes those readings; it does not promise the same protection next time. Compare like-for-like sensor positions and observation periods. Air readings do not measure root temperature. The lowest recorded inside value is not a plant-hardiness recommendation.
How to use this log
- Set inside and outside min/max thermometers to cover the same overnight observation period, using comparable and appropriate sensor positions.
- Record the date ending the night and both minimum readings in degrees Celsius. Add one paired observation per date.
- Read the chart and table together. Export the CSV to keep a copy; the browser-local log holds up to ninety nights.
A measured difference is not a promise for the next night
If your instruments record an inside minimum of 2°C and an outside minimum of −1°C for a night, the recorded-minimum difference is 3°C. That does not establish a constant three-degree advantage. The two minima may have occurred at different times, and another night can produce a different pattern.
What the result means
The chart starts empty and uses only your entered readings. Points are spaced by their actual dates; a line joining two recorded nights does not supply the missing observations between them. The lowest inside reading is a record of that location and period, not a guarantee about roots, another part of the structure or a plant’s survival.
Questions before you start
Where are my readings stored?
In local storage in this browser, using the same log previously used in the greenhouse and winter-gardening guides. There is no account or server upload. A different browser or device will not automatically have your readings.
How do I keep or remove the record?
Use Download readings to export a CSV before changing devices or clearing browser data. Clear readings removes this log from the current browser. If storage is unavailable, export before leaving the page.
Put it in context
Use these guides alongside the tool for the choices a calculation or decision form cannot make for you.