In winter, gardeners in Perth’s hills and inland areas need to keep an eye out for frost. This occurs when temperatures fall to 0 degrees C or below, when the weather is calm and the ground moist.

Most plants that originated in cool climates show no ill effects from a dusting of frosty ice crystals. However, we grow plants from a wide range of climates in Perth and south-west Western Australia. Tropical species, like frangipani, can be killed by frost and others from warm climates can be ‘scorched’ by the freezing conditions.

Frost damage occurs when plant tissue freezes. This causes the plant’s cells to shrink which forces water into spaces between the cells. The actual damage occurs during the thawing process. If thawing is quick and the water can be absorbed back into the cells there is no damage. However when thawing is slow, the cells deprived of water become dehydrated, resulting in frost burn. New shoots on tender plants are particularly susceptible and frost in late winter, when stone fruit trees are in flower, causes the flowers to die, reducing fruit crops.

There are many things that gardeners can do to reduce frost damage. Select frost tolerant plants for garden areas prone to frost. Grow frost sensitive plants like tropical species and succulents in pots and move them under verandas during the cooler months

Old net curtains and shadecloth can be placed or wrapped around outdoor plants as protection on cold nights. Cold air sinks and warm air rises so frost is always worse in low lying areas where frost tolerant plants should be planted.

Applications of seaweed tonic have been shown to thicken the cell walls of the plants so they are better able to cope with heat, drought and frost. Spray liquid seaweed over the leaves at least four or five days before frosty weather is forecast.

The acrylic polymer Drought Shield also reduces frost damage by helping the plant maintain a positive water balance in its cells. Spray the protective coating on the leaves of susceptible plants every 30 days when frost is suspected.

If plants do get frost burnt, don’t remove damaged foliage as it offers some frost protection to undamaged leaves. Avoid heavy fertilising before winter, which will encourage new frost tender growth.

Frost transforms the garden under a pretty dusting of ice crystals and is not all bad as it helps create intense autumn colouring in deciduous plants and kills many plant pests and their eggs.

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This is intended as general information only. Please ask one of our qualified horticulturists for more specific advice on your garden situation.