Frost Protection in Your Garden

Depending on how severe it is, frost damage may present itself as:

• Browning leaf margins
• Water-soaked spots on the foliage
• Blackened or brown patches on young shoots, stems and leaves, and/or collapsed stems
• Eventually, the leaves, stems or shoots become mushy and subsequently rot.

Frost damage doesn’t necessarily mean you will see icicles or a layer of white powder over the leaves. Most plants don’t suffer from frost damage until the temperature drops below 0°C. Once it’s below the freezing point of water, ice crystals can form inside plant cells and cause the inside of the cell to rupture. This is known as intracellular freezing and gives the plant foliage or stems a blackened, brown or burnt appearance. Similarly, a freeze can also cause plant cells to shrink, forcing water from inside the cell into the space between cells, known as extracellular freezing. This turns water to ice, but once it begins to thaw, the water returns to the shrunken cells – if this process happens too quickly, cells burst and plant parts wilt and/or blacken.

While it’s tempting to prune off the damaged growth, don’t. Pruning will stimulate soft, new growth and this is particularly vulnerable to frost. It’s best to wait until the last chance of frost has passed before undertaking any pruning. If night temperatures are less then 5°C at night, there is a good chance frost is still expected. For more detailed information on frost potential, check frost maps on the Bureau of Meteorology.

Until the risk of frost has passed, you will need to provide frost-affected plants with protection, especially as repeated freezes can severely damage or kill plants. See How to protect from frost.

When no more frost is expected, prune to remove the damaged growth. Feed with a complete fertiliser, like Yates Dynamic Lifter Soil Improver & Plant Fertiliser to nourish the soil and gently feed the plant.

Unfortunately, if plants are completely wilted and blackened, it’s unlikely they’ll bounce back. Remove and add to green waste or the compost bin.

There are certain plants are that more susceptible to cold and frost. Most are native to or grow in tropical, subtropical, and warm climates. As such, they have not developed avoidance of intracellular freezing. You may still be able to grow them in your area, but extra frost protection is required. These plants include:

• All summer vegies, including Tomatoes, Pumpkin, Sweet Potato, Cucumber, Corn, and Eggplant
• Avocado (mildly frost tolerant, i.e., if conditions only stay at 0°C for less than one hour)
• Banana
• Citrus, including Lemon and Lime, but Cumquat, Grapefruit, Orange, Mandarin, and Yuzu are slightly more frost tolerant
• Geraniums
• Frangipani
• Hibiscus
• Tree Ferns
• Temperate stone fruit, including Peach, Plum, and Cherry trees

Frost-tolerant is not the same as frost-hardy. Frost-tolerant can cope with frosty conditions for a day or two, but may suffer with continuous exposure, especially if there is no protection. Frost-hardy are tougher and will survive several days of cold and frost. However, all plants must be well-established before heading into their first winter, otherwise they may not be able to withstand the extreme cold.

Here is a list of frost-tolerant and frost-hardy plants. The list is not extensive, so always check plant labels prior to purchase.

include, but are not limited to:

• Abelia
• Azalea
• Correa
• Dianella
• Nandina
• Some varieties of Banksia, Callistemon, Grevillea, and Eucalypt

Vegies

• Broccoli
• Carrot
• Cabbage
• Cauliflower
• Kale
• Pea
• Silverbeet
• Turnip

Shrubs & Grasses

• Azalea
• Buddleja
• Hebe
• Hydrangea
• Indian Hawthorn
• Lomandra longifolia
• Liriope
• Santolina
• Spiraea
• Viburnum tinus

Trees

• Cootamundra Wattle
• Deciduous trees, including Crepe Myrtle, Ornamental Pear, Maple, Oak, and Flowering Cherry
• Rhododendron
• Magnolia
• Some varieties of Banksia, Callistemon, Hakea, and Grevillea