How to Protect Flowers from Frost: A Florist Guide
Frost can devastate your garden in a single night, but with proper preparation and quick action, you can save your beloved flowers. Here's everything you need to know about protecting your plants from freezing temperatures.
Understanding Frost and Its Impact
Frost occurs when temperatures drop to 32°F (0°C) or below, causing ice crystals to form on plant surfaces. This freezes the water inside plant cells, rupturing cell walls and causing permanent damage. Tender annuals, tropical plants, and newly planted flowers are most vulnerable, while many perennials can tolerate light frosts.
Types of Frost
Light Frost (29-32°F): Damages tender plants but hardy species may survive.
Moderate Frost (25-28°F): Kills most annuals and damages semi-hardy perennials.
Hard Freeze (below 25°F): Destroys all but the hardiest plants and can damage woody stems.
Preparing Before Frost Season
Know Your Frost Dates
Learn your area's average first and last frost dates. Your local agricultural extension office can provide this information. Monitor weather forecasts regularly as temperatures begin to drop in fall or when late spring frosts threaten.
Choose Appropriate Locations
Plant tender flowers in protected microclimates near south-facing walls, under eaves, or in areas sheltered from wind. These spots stay several degrees warmer than exposed areas. Avoid low-lying areas where cold air settles.
Maintain Healthy Plants
Well-watered, healthy plants withstand cold better than stressed ones. Water thoroughly before a frost—moist soil retains heat better than dry soil and releases warmth overnight. However, avoid watering frozen ground or leaves.
Protection Methods
Covering Plants
This is the most common and effective method for temporary protection.
What to Use:
Frost blankets or row covers (best option—allow light and air through)
Old bed sheets, blankets, or tablecloths
Burlap
Cardboard boxes
Large plastic buckets or pots (for individual plants)
Agricultural fabric (reusable for multiple seasons)
What to Avoid:
Plastic sheeting touching foliage (conducts cold and can cause more damage)
Heavy materials that crush delicate flowers
How to Cover Properly: Drape covers over plants in late afternoon before temperatures drop, extending material all the way to the ground to trap warm air rising from the soil. Use stakes, hoops, or tomato cages to keep fabric from touching flowers—contact with frozen material can damage blooms. Secure edges with rocks, bricks, or landscape staples to prevent wind from blowing covers off. Remove covers in the morning once temperatures rise above freezing so plants don't overheat.
Mulching
Apply a 2-4 inch layer of organic mulch (straw, shredded leaves, pine needles, or wood chips) around the base of perennials and shrubs. Mulch insulates roots and helps soil retain heat. For extra protection during severe cold, mound additional mulch over the crown of perennials, but remove it in spring once danger passes.
Watering Before Frost
Water plants thoroughly the day before expected frost. Wet soil absorbs and holds more heat than dry soil, releasing it slowly overnight. This can raise the temperature around plants by several degrees. Avoid overhead watering if frost is imminent, as wet foliage freezes more readily.
Creating Windbreaks
Wind accelerates heat loss. Install temporary windbreaks using stakes and burlap, or position portable screens around vulnerable plants. Even reducing wind speed by half can raise temperatures significantly.
Using Heat Sources
For small, prized plants, you can add supplemental heat:
String Lights: Old-fashioned incandescent Christmas lights (not LEDs) generate modest heat. Drape them over plants before covering, ensuring bulbs don't touch foliage.
Water Jugs: Fill dark-colored containers with water and place near plants during the day. Water releases stored heat overnight.
Cloches and Hot Caps: These individual covers trap heat and work well for seedlings and small plants.
Bringing Plants Indoors
Container plants and hanging baskets can be moved to garages, sheds, porches, or inside your home. Even an unheated garage provides protection from frost. Move plants back outside once temperatures moderate.
Special Considerations
Container Gardens
Pots are more vulnerable because roots are exposed on all sides. Move containers against the house, group them together for mutual protection, or insulate pots with bubble wrap, burlap, or extra mulch. Elevate containers slightly to prevent cold transfer from frozen ground.
Roses
Tender roses need extra protection. After the first hard frost, mound 8-12 inches of soil or mulch around the base. In very cold climates, create wire cages around bushes and fill with leaves or straw, or wrap plants in burlap.
Spring-Flowering Bulbs
Early bloomers like tulips and daffodils are surprisingly frost-hardy once established. However, protect emerging shoots and open blooms with lightweight fabric during unexpected late frosts. The foliage will likely survive even if flowers are damaged.
Tropical and Subtropical Plants
Hibiscus, bougainvillea, citrus, and similar plants cannot tolerate any frost. Bring these indoors well before first frost, or plan to grow them as annuals in cold climates.
What to Do After Frost Damage
If frost strikes before you can protect plants, don't panic immediately:
Wait and Assess: Damaged foliage may look terrible initially but plants often recover. Wait several days to see the full extent of damage before taking action.
Don't Prune Right Away: Resist the urge to cut off damaged growth immediately. Dead foliage actually provides some protection for underlying tissue. Wait until spring to prune damaged portions.
Water Gently: If plants froze, water them gently in the morning to help thaw tissues gradually. Avoid fertilizing stressed plants.
Provide Shade: Ironically, damaged plants can suffer further injury from bright morning sun. Provide temporary shade to slow thawing.
Long-Term Strategies
Plant Selection
Choose flowers appropriate for your hardiness zone. Incorporate more cold-hardy perennials that return year after year without protection. Native plants are typically well-adapted to local temperature extremes.
Succession Planting
Don't plant all your tender annuals at once. Stagger plantings so that if early ones succumb to late frost, later plantings will fill in.
Hardening Off
Gradually acclimate greenhouse-started or indoor plants to outdoor conditions over 7-10 days. This toughens them up and improves frost tolerance.
Extend the Season with Structures
Cold frames, hoop houses, and greenhouses extend your growing season at both ends, protecting flowers from early fall and late spring frosts while creating beautiful garden spaces.
Quick Reference Checklist
When frost threatens, act quickly:
Water plants thoroughly in the afternoon
Gather covering materials
Cover plants before sunset
Extend covers to the ground and secure edges
Add supplemental heat if needed (lights, water jugs)
Check weather for consecutive frost nights
Remove covers mid-morning once temperatures rise
Re-cover if additional frost nights are forecast
With vigilance, preparation, and these protective measures, you can successfully shepherd your flowers through cold snaps and enjoy blooms throughout the growing season. The key is staying informed about weather conditions and acting proactively rather than waiting until frost has already struck.
