Tremendous variability exists within each plant species and their tolerance to cold. However, even plants in the correct zone may suffer from cold damage.
Sometimes it isn't really the cold temperatures that cause problems, but the fluctuations between warmth and cold. Using plants that are reliably cold hardy and keeping plants healthy during the growing season is the first step in protecting plants from cold damage
Emerging flowers and leaves are most prone to frost damage. With below freezing temperatures, water in plant cells freezes forming ice crystals that expand as they freeze and rupture cell walls.
The best prevention against frost damage to flowers is to keep buds from opening too soon. Mulch also keeps soil temperatures cold.
Frost heave occurs after the soil has been exposed to freezing temperatures. The pressure that is created from alternating freezing and thawing of the soil lifts the soil and plants up and out of the ground exposing them to cold and drying winds
Heaving can be reduced by applying a layer of mulch of wood chips or shredded leaves.
Ice formation on the plant and in the plant tissue is what causes the damage, especially when the tissue thaws. Dormant plants are susceptible to freezing injury. Flower buds are most often affected.
When planting in pots use a thick pot with a large soil volume which will provide better insulation. You can also wrap with straw and place pot in a protected spot to decrease the risks.
Clay pots will break if subjected to freezing temperatures so opt for plastic pots or bury pots in the ground and mulch the area to insulate warmth.
Frost cracks are often the result of some sort of weakness in the bark which occurred to the tree earlier. During the rapid temperature changes throughout winter the inner bark expands and contracts, the damaged wood does not contract to the same degree as healthy wood causing the wood to split resulting in frost crack.
Wrapping with tree wrap may give protection against frost cracks.
Evergreens release water through there leaves during photosynthesis process even in cold weather. When a plants cannot replace this released water due to the frozen ground, they will dehydrate. Winter burn shows up on evergreens as brown to red, dry foliage or needles. Most damage is shown on the sunny side areas as the sun’s rays increase photosynthesis and more water is released.
Evergreens should enter winter well-watered. Continue to water during winter when the soil is not frozen to increase moisture intake. Soil moisture can be conserved by adding a layer of mulch after the soil has gotten cold.
Weather can be extremely unpredictable, so plan your planting in advance - plant location and choice, and provide sheltered areas for your prized specimens. This will help ensure your plants survive the winter. Contact Eastern Suburbs Horticulture on 0413 328334 for all your horticultural advice