When winter begins to lift and the tender shoots of perennials emerge, an overnight frost can quite literally nip new growth in the bud. Even in mild-winter regions, frost can have damaging effects on cold-sensitive garden favorites like citrus trees, bougainvilleas, fuchsias, salvias and succulents. Luckily, many plants can be saved from harm when the temperature dips below the freezing point (32 degrees Fahrenheit, or 0 degrees Celsius) with a few simple precautions.
Check the forecast. In early spring (or throughout winter in mild climates), pay attention to weather forecasts. For nights when a freeze is predicted, gather basic supplies, such as frost blankets (available at nurseries) and stakes, or invest in more expensive cold frames and cloches.
Cover plants before nightfall. If a frosty night is forecast, cover tender plants like angel’s trumpet (Brugmansia spp.), bougainvillea, citrus, fuchsia, penstemon, salvia, succulents and tree ferns. Young plants and those that have been recently planted can be more vulnerable to frost damage than well-established ones.
To cover plants, place stakes around small to medium-size plants and drape frost blankets over the stakes so that, ideally, the blanket covers but does not touch the plant. For larger plants like gardenia and tree ferns, drape coverings over the crown and wrap the trunk. Always remove the covering in the morning. Forgot to buy frost blankets? Old bed sheets or lightweight blankets can be used as well and are preferable to plastic tarps.
Use a cold frame. To extend your potential for growing cold-tender plants — such as potatoes, lettuce, spinach and other edible greens — and get a jump-start on starting spring seedlings, consider investing in cold frames. These glass-topped frames trap heat and moisture, creating a greenhouse environment for tender plants.
Protect sensitive plants with cloches. Named for the French word for “bell,” glass cloches work like cold frames on a smaller scale by creating warm, moist environments for tender plants and seedlings in the ground. Place cloches over small plants in the afternoon, and the trapped warmth will help the plants survive a frosty night. Cloches used to cover plants in full sun can get too toasty on a warm day, so either remove them or put a wedge of wood under one side to allow ventilation. Plastic gallon milk jugs can be cut and used as an inexpensive — if less charming — alternative to cover tender plants in beds.
Spread mulch. Help protect the shallow roots of tender shrubs and perennials from ground freezes by spreading a 3- to 4-inch layer of wood chip or straw mulch. Mulch can be purchased at nurseries and garden supply stores by the bag or in bulk.
Bring small potted plants indoors. The easiest way to protect succulents and tender herbs from an overnight freeze is to bring them inside. If you have a sunny spot for them, keep them indoors through the cold weather. Otherwise, bring them back outside during the day.
Move large potted plants under eaves. Cold wind can intensify the harmful effects of frost by removing moisture from foliage faster than the plant can take up water from the roots. To cut down on this damage, move larger potted plants to sheltered areas, such as under the eaves, beneath the canopy of large trees or into the garage for the night. Provide extra protection by wrapping the plants with frost blankets.
Water well. It may seem counterintuitive to water a garden before a freeze, but providing frost-tender plants with a good drink in the daytime makes plants better able to withstand colder night temperatures. Water early in the day so that the plants have time to absorb moisture before the temperature drops. Avoid spraying the foliage, which can freeze if not given time to dry off.
Wait to cut back frost-damaged plants. Although brown foliage and crispy stalks look unattractive, the damaged growth actually helps protect the lower parts of the plant from future freezes.
Hold off on pruning plants that have been damaged until all risk of nighttime freezes has passed. If you cut back the plant too early and have more nights with frosty temperatures, the shock of pruning and freezing can kill the plant.