Symptoms
Signs of frost and cold damage can often be confused with the effects of pests and diseases.
Frost and, more specifically, alternate freezing and thawing can destroy plant cell walls, often killing tender plants, but hardier species can be affected as well.
Bedding plants and tender vegetables, such as potatoes and tomatoes, show a range of symptoms in cold weather: leaf darkening or yellowing, leaf curling, scorch, tissue destruction and even plant death.
Hardier plants may show signs of leaf scorch: browning, drying and even paper-like thinning of the leaf tips and margins. Cold, wet soil, cold winds and low night-time temperatures can cause reddish-purple leaf discolouration. Photinia is particularly prone to this reaction (not to be confused with their red-flushed new leaves). Rhododendrons and Viburnum ryitidophyllum often suffer temporary leaf curling and drooping in cold weather. Camellia and magnolia flowers can be ruined by a single frost.
Frost
can damage apples when the fruits are only marble-size, causing
brown corky layers to form at the flower end of the fruit
('Bramley's Seedling' seems most susceptible). Strawberry
flowers damaged by frost exhibit characteristic 'black eye'
symptoms, where the centre of the flower turns black. Damaged
flowers don't develop into fruit.
Prevention
Choose planting positions carefully to avoid 'frost pockets' (where cold air settles at the bottom of a slope), or a position in early morning sun. Don't apply nitrogen-rich fertilisers late in the season as they stimulate soft, sappy growth which is especially vulnerable to cold damage. Cover plants with a double layer of horticultural fleece when frosts are forecast.
Cure
If no more frost is expected prune out any damaged growth, cutting to an undamaged sideshoot or bud. Otherwise delay pruning until weather is more settled. After pruning apply a top dressing of a general-purpose fertiliser such as Growmore at the manufacturer's recommended rates to encourage strong re-growth.