First frost is forecast: what should I protect tonight?
Use the lowest hourly temperature, crop tenderness and your garden's cold pockets to decide what needs cover before sunset.
Answer first
Protect tender fruiting crops, basil, dahlias and exposed seedlings when the overnight forecast approaches 2°C; air near the soil can be colder than the standard forecast height. Harvest anything already ripe, water only if the soil is dry, and put breathable cover in place before sunset so it traps stored ground heat.
Make the decision in three passes
Start with the lowest hourly forecast rather than the daytime headline. Then check which plants are tender, and finally adjust for the exact bed: low, open and wind-sheltered places often cool faster than raised or wall-side beds.
The Garden Dream frost panel is a warning aid, not a thermometer at leaf height. If your garden has frosted before while the nearest forecast stayed above zero, use that local history as the stronger signal.
- Cover now: tomato, pepper, cucumber, courgette, basil, dahlias and young tender seedlings.
- Usually tolerate a light frost: kale, mature spinach, leeks and many established brassicas.
- Harvest first: ripe tomatoes, cucumbers, beans, basil leaves and cut flowers you do not want to lose.
- Move containers beside a wall or under an unheated roof; roots in pots cool faster than roots in open soil.
Cover without creating a second problem
Use horticultural fleece, row cover, a sheet or another breathable layer. Support it above fragile foliage where possible, anchor every edge, and extend it to the soil so heat cannot escape freely. Plastic can transfer cold where it touches a leaf and can overheat plants quickly after sunrise.
Put the cover on before sunset. Remove or vent it the next morning once temperatures rise, especially in direct sun.
A heavy row cover can protect more than a light insect mesh, but it also blocks more light. Use the product's stated frost protection rather than guessing from thickness.
What the forecast cannot tell you
A forecast grid cannot see every hollow, courtyard, slope or windbreak. Cloud, wind and soil moisture change how quickly a garden loses heat, while the official air temperature is measured above the ground. Keep a simple note of the forecast and what actually frosted; after a few events, your own garden offset becomes more useful than a generic threshold.
If several hard-freeze hours are forecast, a light cover may only delay damage. Prioritize harvesting and moving containers rather than promising complete protection.
Useful next actions
Sources and method
- Extending the growing season: start early, end later — University of Minnesota Extension
- Protect strawberries from spring freeze and frost — University of Minnesota Extension
Read how Garden Dream calculations and editorial review work.
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