Frost Protection Planner Calculator Guide
Use this frost protection planner to choose cover strategies based on forecast low temperature and plant hardiness. Enter expected overnight low in °F and whether plants are tender, semi-hardy, or hardy to get a recommended protection method.
How to use the frost protection planner
Enter the forecast overnight low temperature in Fahrenheit and select plant hardiness: tender (tomatoes, basil), semi-hardy (lettuce, pansies), or hardy (kale, spinach).
The planner recommends protection level from none to heavy covers or moving pots indoors.
Frost protection threshold formula
Protection level = f(expected low °F, plant hardiness). Above 32°F: no protection needed. Light freeze (28°F < temp ≤ 32°F): tender plants need covers or indoor move; semi-hardy benefit from light fabric; hardy often survive. Severe freeze (≤ 28°F): tender and semi-hardy need heavy protection or indoors; hardy benefit from heavy fabric.
Wind and duration matter — a brief 31°F radiative frost differs from a prolonged 28°F advective freeze.
- Tender: damaged at light frost (~32°F)
- Semi-hardy: tolerate light frost with cover
- Hardy: survive light freeze; may need cover below 28°F
- Cover before sunset; remove mid-morning after thaw
Worked example
Forecast low 30°F with tender tomato seedlings in the ground: this is a light freeze for tender plants.
Recommendation: cover with light frost cloth or sheets, or move potted plants indoors. Water soil in afternoon — moist soil holds heat better than dry soil.
Protection materials ranked
Floating row cover (frost cloth) adds 2–4°F of protection. Sheets and blankets add more when draped without crushing plants. Plastic sheeting traps heat but must not touch foliage — use hoops. Heat lamps and Christmas lights (non-LED) add degrees in cold frames.
Microclimate tips
Low spots collect cold air — cover plants in valleys first. South walls and patios radiate stored heat. Group containers together and wrap pots to protect roots.
- Check seed starting and transplant dates against late frost risk.
- Have covers ready before the forecast — install at dusk.
- Mulch root zones of hardy perennials before first hard freeze.
- Use harvest date planner to avoid planting too early for your zone.