In contrast, the hardy apple trees are looking fine, leaves still attached. Some trees respond well to a blast of frost. The large deciduous nashi pear tree is now a beautiful flame red.
How frost works
Ice forms inside plant tissue and damages the plant cells. This will damage or kill the leaf, particularly if the foliage thaws quickly in the morning sun.
On the land, cooler air settles in hollows, creating frost pockets. Clear nights in winter often produce frost, but cloud can insulate the land from temperature extremes.
Cloud often sits at a certain elevation on mountains and will create an insulated "inversion layer" of warmer temperatures in an otherwise cold location.
An example of this can be seen at Landsendt Subtropical Gardens in Oratia, West Auckland. The garden is higher up in the Waitakere ranges where this insulated inversion layer sits.
Dick Endt's plant collection features a wide range of exotic subtropicals, many from South America.
Plants fall into four freeze-sensitivity categories: (1) tender; (2) slightly hardy; (3) moderately hardy; and (4) very hardy. Tender plants from a subtropical origin are most at-risk in temperatures on or slightly below zero. Heavier frosts below 2C will start to affect hardier species.
When some plants go through a period of cold, they will harden against freeze injury, but a frost after several warm days will cause more damage as the plant has lost its hardiness. This is why spring frosts cause so much damage. For more info on a range of plants and their frost hardiness, go to: www.fao.org/docrep/008/y7223e/y7223e0a.htm
Outwitting Jack Frost
Fruit trees and ornamentals
Spring frosts cause serious damage to early fruit tree blossom and buds in deciduous fruit trees and grapevines. Commercial orchards and vineyards go to great expense using helicopters to drive down the warmer layers of air to prevent frost from forming. Some orchards have sprinklers that pulse on frosty nights.
The latent heat created when the water freezes prevents the plant foliage from dropping below 0C.
As most home gardeners are not able to do this, it's worth choosing fruit trees that bloom later in the season to insure against the risk of frost in spring, or cover trees with frost cloth where possible.
A good idea is to plant a shelter belt uphill from your garden, to filter some of the cold air that flows down from higher ground.
Spraying with biodynamic "Valerian Prep" also helps protect against late frosts.
Young evergreen trees are particularly susceptible to frost damage, which is why it makes sense to plant hardy, quick-growing "pioneer" species first to provide canopy shelter for sensitive plants.
Before planting new trees or shrubs, research how hardy the plant is.
If your plant is tender, ensure you plant on the warm side of a wall or near taller trees or shrubs for shelter.
Resist cutting back frost-damaged foliage until spring. Despite being unsightly, the brown foliage will protect the rest of the plant.
You'll find most plants, unless they're very young, have reserves of strength and will produce lush new growth as they're warmed by the spring weather.
Vege garden
• Use straw to cover sensitive plants. Put up a cloche frame and use frost cloth when the overnight forecast is on or below zero, or keep your veges permanently in a cloche frame covered in glasshouse film.
• Root veges such as carrots and parsnip often become sweeter with a dose of frost.
• Members of the brassica family are also frost tolerant.
• A silver lining: frost will help kill off some of the overwintering pests and diseases in your garden.
