Rainfall and frost tolerance are the two most important factors to consider when selecting your plants. Frosts occur at night when temperatures drop below zero and there is no wind and clear skies. That is when water forms into minute needles of ice on cold surfaces and in the morning everything is covered with the silvery beauty of frost.
Many plants have adaptations that help them cope with cold and frost. Generally tropical plants have large, lush leaves and this large surface area makes them tender to frost. Plants with small or fine leaves are generally hardier to frost. For example, conifers have fine foliage that is tough, leathery and angled, preventing frost from settling on the leaves and doing damage. Choose varieties like Juniper horizontalis that come from cold regions. Plants that have small leaves that are densely packed together, such as Escallonia, Veronica and English box are also hardy to frost.
Another frost adaption is tough, leathery foliage that helps protect from the severity of frost and ice; like Viburnum tinus and Camellia. Deciduous plants like maples, magnolias, betula and flowering cherries that drop all their leaves have no foliage that could be affected by frost. There are degrees of frost tolerance and many plants will grow in a fairly wide range of temperatures; but there is a clear distinction between those that are able to tolerate severe frost and those that will only take mild frost. Remember that many evergreen plants may drop some of their leaves or become totally deciduous in cold regions. Water in the mornings, once your plants have thawed out; this allows the soil to drain and warm up again during the day.
There are several ways to lessen frost damage, especially in severe frost belts. Planting hedges and windbreaks and building walls and fences can create sheltered areas in the garden where more tender plants can be grown. Cold air is heavy and accumulates naturally in low lying areas or gullies, and frost occurs. Bear this in mind when installing hedges and walls as they can create blockages and trap cold air if they are placed incorrectly. Always ensure that there is an exit point at the lowest level to allow the cold air to drain away. Warm north facing walls will radiate heat and benefit more tender plants growing nearby.
Many beautiful trees and shrubs may be more vulnerable to frost when young, but fully hardy once they are established. Protect these by covering them for the first few winters with a special plant cover like Kaycover or Cropguard. This lighweight material can simply be thrown over shrubs and secured to the ground with something heavy like bricks. No need for stakes etc. and the cover lets in enough light so it does not need to be removed during the day. Putting down a very thick mulch of shredded newspaper, autumn leaves, dry grass cuttings, bark, straw, or any other organic material will protect the roots of tender shrubs, and even if they do get frosted, should shoot again in spring. Larger plants like palms, tree ferns and tender trees can be covered in winter and their main stems protected with hessian or other plant protector covers which have been cut into strips, Bandage the stems thickly but not too tightly and secure the ends. The smaller branches may still get frosted but the plant should shoot again in spring.
Special anti-transpirant sprays like Wilt-pruf are available which place a protective membrane over the leaves of the plants, making them more frost tolerant. If you do get frost damage in your garden, resist the temptation to prune it off until spring, because even dead foliage will protect the leaves underneath. Pruning will just encourage new growth which is lush, tender and susceptible to frost damage. If a severe frost strikes you can minimise severity of the damage by quickly spraying the leaves of your tender plants before the sun hits the plant.
Early autumn is a good time to plant hardy plants as this gives them time to settle before winter, improving growth in summer. More tender plants should be planted in spring once all danger of frost is over.