How to Protect Plants From Frost | Before the Cold Hits

Protecting plants from frost means moving containers indoors or covering in-ground plants with breathable material that reaches the soil.

For the full breakdown, see our best Protection For Plants guide.

When temperatures drop into the mid-30s °F, tender plants need help. The working method is simple: trap the heat rising from the soil under a cover that never touches the foliage. Do it before nightfall while the day’s warmth is still in the ground, and your garden makes it through the night. Below are the steps that work, the mistakes to skip, and which plants actually need the effort.

When Do Plants Actually Need Frost Protection?

Start paying attention when the forecast calls for temperatures in the mid-30s °F or lower. A light freeze around 30-32°F can often be handled with a simple sheet, but a harder freeze — think 28°F for five hours — demands more substantial protection, as the Iowa State University Extension notes.

The plants most at risk are the ones with the least resilience:

• Potted tropicals and annual containers, where roots are exposed to cold air on all sides
• Seedlings and young transplants with shallow root systems
• Frost-sensitive vegetables like tomatoes, peppers, and squash
• Tender perennials and small shrubs that haven’t fully hardened off

Established trees and hardy perennials usually shrug off a spring frost. Watch the young, the potted, and the tropical.

Covering Plants: The Right Way and the Wrong Way

The goal of a cover is not to keep the cold out — it’s to trap the radiant heat rising from the soil. That means the cover must reach the ground on all sides and stay off the foliage.

Iowa State and Michigan State University Extension both recommend breathable materials: sheets, blankets, towels, burlap, row covers, frost fabric, or tarps. Drape the material over a support structure such as stakes, PVC pipe, sawhorses, or patio furniture so it doesn’t rest on the leaves — contact transfers cold and can damage the plant.

Seal the edges to the soil with rocks, bricks, or landscape pins, then keep the cover in place through the whole freeze event. After sunrise, once temperatures rise above freezing, remove the covers.

The one material to handle with care is plastic. Clear plastic traps heat well, but if it touches the foliage, it can cause serious damage. Only use plastic on a frame that keeps it suspended well off the leaves.

Supporting Steps That Give Plants a Better Night

A few extra moves before dark make a real difference in how plants weather a freeze:

• Water the soil beforehand — moist soil holds more heat than dry soil. Iowa State recommends watering before a freeze, but avoid soaking or watering so late that plants stay wet through the cold night.
• Add a layer of mulch around root zones with straw, bark, or leaves — about 2 to 4 inches deep — keeping it pulled away from stems and trunks to reduce rot risk.
• Use cloches for small plants — upside-down containers, milk jugs with the bottoms cut off, or rigid vented caps work well for seedlings and individual specimens.
• Bring containers indoors — a garage, shed, porch, or heated room is the simplest and most reliable protection for potted plants.