What Is a Freeze?
A freeze occurs when temperatures drop below the freezing point of water (32° F or 0° C). When the water inside a plant freezes, it can cause the plant cells to burst, resulting in irreparable damage.
What Is Frost?
Frost occurs on clear, still nights. As the air temperature approaches freezing, the surface temperature of plants can dip below freezing, causing ice crystals to form in the same manner that dew forms on warmer nights. Because temperatures vary just a few feet above the ground, frost can form when your thermometer reads above freezing. Freezing temperatures may or may not be accompanied by frost.
How to Protect Tender Plants from Frost or Freeze Damage
If frost is predicted in your area, you may want to take steps to protect vulnerable plants such as:
• Houseplants and tropicals.
• Spring-blooming shrubs and trees such as azalea, rhododendron, and cherry.
• Citrus trees. • Tender bulbs such as dahlia and elephant ear.
• Warm-season vegetables such as tomato, corn, and pepper.
• Warm-season annuals such as impatiens, petunia, and geranium.
Shrubs can be covered with a blanket to protect them from a late spring frost.
Steps to take when frost or freeze threaten tender plants:
• Bring Indoors: Frost-tender plants in containers should be brought inside during cold weather. Dig up tender bulbs and store them in a cool dry place.
• Water Plants: Water plants thoroughly before a freeze to prevent desiccation and to add insulating water to the soil and plant cells.
• Protect Tender Sprouts: Cover tender plants overnight with an inverted bucket or flower pot, or with a layer of mulch. Be sure to uncover them in the morning when the temperature rises above freezing.
• Cover Shrubs and Trees: Larger plants can be covered with fabric, old bed sheets, burlap, or commercial frost cloths (avoid using plastic). For best results, drape the cover over a frame to keep it from touching the foliage. Fabric covers help to trap heat from the soil, so make sure your cover drapes to the ground. Uncover them in the morning when the temperature rises above freezing.
• Assess Losses: Hardy perennials, trees, and shrubs may recover from a late spring freeze, even if visibly damaged. Their blooms and fruit may be lost for the year, but once they begin actively growing you’ll be able to determine and remove any permanent damage to stems and branches. Frost-tender plants will not recover at all, so avoid planting them until you’re confident that freezing weather has passed.
• Practice Prevention: Choose plants that are hardy for your climate zone, or plant tender plants in containers that can be brought indoors. Avoid applying fertilizer until after the last frost, to prevent a flush of tender growth that can be damaged by the cold.