Frost is the defining risk of fall gardening. A single cold night can blacken tender plants, split fruit, and end the growing season for crops that were still producing, while a few degrees of protection can keep the same plants growing for weeks longer. Fall frost protection is not about fighting winter — it is about buying time. A row cover, a cloche, a cold frame or a simple fleece wrap can add several degrees of warmth on a frosty night, and that is often the difference between a harvest and a loss.
The key to frost protection is knowing what frost is, which plants are vulnerable, and when to act. Frost forms on clear, still nights when heat escapes from the ground into the sky, and it is worst in low spots where cold air collects. A forecast of frost means you should cover vulnerable plants in the evening and uncover them in the morning. This guide explains how frost works, which plants to protect, and which methods work best, so you can protect what matters and let go of what does not. If you are unsure about frost in your area, check your local extension service.
How frost damages plants
Frost damages plants because water inside plant cells freezes, expands, and bursts the cell walls. Tender plants with soft, watery leaves are damaged first, and their leaves turn black and mushy after a frost. Hardier plants can take a light frost, and some, such as kale and Brussels sprouts, taste better after it. The damage depends on how cold it gets, how long it stays cold, and how wet the plant is: a light frost on a dry night does less damage than a hard frost on a wet night, and a plant that is already stressed by drought or disease is more vulnerable than a healthy one.
First frosts are averages, not dates. Average first frosts fall in the September range in the coldest zones, in October across much of the middle of the country, and in November or December in warm zones, with zones 11 to 13 largely frost-free. These are averages and ranges only, and a single cold night can arrive earlier than the average, so watch the forecast rather than the calendar. Use our frost date calculator to find the average dates for your zone, and remember that a low spot in your garden can be several degrees colder than a sheltered spot near a wall.
Which plants to protect first
Protect tender plants first: tomatoes, peppers, courgettes, beans, basil and other summer crops that are still producing, and any plant that is only just hardy in your zone. Basil is the most frost-tender plant in most gardens and is damaged by cold well before frost — see our growing basil guide. Lettuce, salads and herbs such as cilantro and parsley can take a light frost but are damaged by a hard one, so they are worth covering on cold nights. Our fall vegetable care and fall herb care guides cover which crops to protect and which to harvest.
Hardy plants such as kale, Brussels sprouts, carrots, parsnips and beets need little or no protection from a light frost, and they often taste better after it. Root crops can stay in the ground through light frosts if they are mulched, but they must be lifted before the ground freezes hard. Newly planted trees, shrubs and perennials are worth protecting in their first fall, since their roots have not yet established, and tender shrubs and roses benefit from a mulch or wrap after the first frosts. See our fall planting guide and fall mulching guide guides for planting and mulching before frost.
Row covers, fleece and cloches
A row cover is the simplest and most effective frost protection for a vegetable bed. It is a sheet of lightweight fabric laid over hoops or directly over the plants, and it traps heat from the soil and adds several degrees of warmth on a frosty night. Horticultural fleece is the usual material: it lets light and water through, it is light enough not to crush plants, and it can be left on for days in cold weather, though it should be lifted in warm weather so plants do not overheat. Cover plants in the evening before a frost is forecast, and uncover them in the morning, or leave the cover on if the weather stays cold and dull.
A cloche is a small, rigid cover placed over individual plants or a short row, traditionally made of glass and now often of plastic. Cloches work well for lettuce, salads and young plants, and they can be moved around the garden as needed. A cold frame is a larger, box-like structure with a glazed lid, which gives more protection than a row cover and can be used to grow salads and herbs through fall and winter. It needs ventilation on sunny days, since it can overheat quickly, and it should be closed in the evening before a frost. Our fall seed starting guide explains how to use a cold frame for seedlings, and our fall vegetable care guide covers covers on vegetable beds.
Watering, mulching and other frost protection
Water the soil before a frost is forecast, since damp soil holds heat better than dry soil and releases it slowly overnight, warming the air around plants. Water in the morning or early afternoon, so the soil is damp but the leaves are dry by nightfall, since wet leaves freeze more easily than dry ones. Our fall watering guide covers watering before frost. Mulch around the roots of vulnerable plants, keeping mulch clear of stems, to keep the soil warmer for longer and protect roots from freeze-thaw cycles — see our fall mulching guide and mulch types guides.
Move pots and containers to a sheltered spot before frost, since pots freeze far faster than the ground, and group pots together against a wall, which radiates a little heat overnight. Wrap pots in bubble wrap or hessian to insulate the roots, and raise them off the ground so cold air does not sit under them. Bring tender plants indoors before frost, as our fall houseplant care guide explains. Do not use plastic sheeting directly on plants as frost protection, since plastic conducts cold and can make damage worse where it touches leaves; use fleece or fabric instead, or support plastic on hoops so it does not touch the plants.
When to give up and harvest
Frost protection buys time, but it does not stop winter, and there comes a point when the sensible move is to harvest rather than protect. If a hard frost is forecast and a crop is nearly ready, pick it rather than risking losing it overnight. Green tomatoes can be ripened indoors, herbs can be dried or frozen, and root crops can be lifted and stored. Our fall harvesting guide covers harvesting before frost. Once tender plants are finished, pull them up and compost healthy material, and put the bed to bed with compost or a cover crop — see our fall soil preparation and fall garden cleanup guides.
Do not protect plants that are already damaged by frost in the hope they will recover, since frost-damaged growth rarely recovers and it can harbour disease. Cut back damaged growth, clear it away, and focus protection on plants that are still healthy. And do not forget that frost is not always the enemy: a light frost sweetens kale, Brussels sprouts, carrots and parsnips, and it kills off pests and disease that would otherwise survive into winter. Work with the season, protect what is worth protecting, harvest what is ready, and let the rest go.
Frequently asked questions
How can I protect plants from frost in fall?
Cover them with horticultural fleece or a row cover in the evening, use cloches or a cold frame, water the soil before frost, mulch around roots, and move pots to a sheltered spot. Uncover in the morning.
What is the difference between a light frost and a hard frost?
A light frost is a brief dip to just below freezing, which damages tender plants but leaves hardy ones unharmed. A hard frost is colder and longer, and it damages or kills many plants, including some that survive a light frost.
When is the first frost in my area?
Average first frosts fall in the September range in the coldest zones, in October across much of the middle of the country, and in November or December in warm zones, with zones 11 to 13 largely frost-free. Use our frost date calculator for your zone, and watch the forecast.
Should I water before a frost?
Yes, water the soil before a frost is forecast, since damp soil holds heat better than dry soil. Water in the morning or early afternoon so leaves are dry by nightfall.
Can I use plastic sheeting for frost protection?
Not directly on plants, since plastic conducts cold and damages leaves where it touches them. Use fleece or fabric, or support plastic on hoops so it does not touch the plants. If you are unsure, check your local extension service.