Garden cold alert

A low of 36°F is forecast. Frost can form on plants even when the forecast low is a few degrees above freezing, especially on clear, calm nights and in low spots. A cover traps heat rising from the soil.

When we suggest this

• ForecastA night at or below about 36°F is forecast for tonight or the next 2 nights.

What would stop us suggesting it

• The morning after the forecast night passes (or when a fresh forecast no longer shows it).
• When you mark it Done or Doesn't apply. "Doesn't fit my setup" stops it for that plant this season.

What to do

1. Before sunset, drape a sheet or frost cloth over tender plants so it reaches the ground on all sides. Don't tie it around the stem.
2. Keep plastic off the leaves. If plastic is all you have, hold it up with stakes or hoops.
3. Move pots into a garage, shed, or porch for the night.
4. Uncover in the morning once it's above freezing and any frost has melted.

What we can't know

• How cold it gets in your yard. Low, open spots can be several degrees colder than the forecast.
• Which plants you've already picked or moved.

NWS offices issue Frost Advisories for forecast lows of about 33–36°F, and NWS Louisville notes frost with official lows as high as 36–37°F on clear, calm nights, because thermometers sit about 5–6.5 ft above the ground where air can be 3–5°F colder. Covers work best on clear, calm nights; they give little protection in windy freezes or below about 28°F. Sources differ on when to uncover: most say the next morning once temperatures rise above freezing, while Arizona Extension suggests waiting until it is about 50°F under the cover.

Where this advice applies

All US regions.

Any US garden with plants growing when a night at or below about 36°F is forecast.

Engine: fire only when at least one growing tender or woody-tender plant (or a plant whose family frostAction level is at or above the forecast low, e.g. an apple in bloom via apple.bloom-frost) is at risk; semi-hardy, hardy, and woody plants are then listed by their own levels. The alert label follows the tiers at the top of this file. Low spots and open lawns run colder than the forecast point; beds against a south wall run warmer.

Exceptions

• Gardens where no growing plant is at risk at the forecast low (see frost classes).
• Plants you've marked finished for the season.
• Nights more than 2 days out; those show as an early look on the Weather page.

Reviewed

Sources checked Sept 2026 · awaiting expert review

Gardenplanner research (AI-assisted), pending extension-qualified review

Rule id and version: general.cold-alert@1