Even though we have fairly mild winters here in the Willamette Valley paying attention to winter care might save some important garden plants in your garden.
Remember the winter of 2012-2013 when we have the December hard freeze event? we got to minus four degrees here at the nursery. A hard freeze is defined as air temperatures below 25 degrees for over four hours. The result of the December 2012 freeze was devastating to many zone 8 plants.
Some of the plants that froze to the ground that winter came back after 12-24 months such as Escallonia, Viburnum Spring Bouquet, Strawberry Tree and others. Some more tender plant like New Zealand Flax succumbed to the cold.
Would covering those plant made a difference that winter? I really doubt it because the temperatures were sub zero and freezing temps (below 32) lasted a week. The devastation was total for many containerized plants that normally would have survived. the problem was the roots froze and the freeze came early in the winter season before plants were completely dormant.
Some things you can do to protect plants is to cover with frost protection blankets, plant bags, and plastic sheets. If you use plastic sheeting it must be removed during the day, especially when the sun is out, or you will toast the plants inside the plastic which acts as a green house.
Wrap small fruit tree and shade tree trunks for sun scald protection. Sun scald can damage the bark and lead to trunk decay and ultimately total loss of the tree. Some paint the trunk with white latex pain diluted with water 50%. This reflects the light and heat to protect the vulnerable bark from scald after cold night time temperatures.
Plant covers can boost temperatures inside the cover by up to 6-8 degrees. That can be enough the eliminate, or minimize freeze damage. Try to make sure the cover comes completely to the ground. The soil temperatures will be warmer than the air temperatures and can radiate up into the space under the cover to warm the plants.
Mulch vulnerable perennials like hardy fuchsias with 6 to 12 inches of mulch like straw or leaf litter. That layer on insulation can prevent the crown of the plant from succumbing the the hard freeze. Roses may also benefit from this mulch because the graft union at ground level in very vulnerable from a hard freeze. Dahlia bulbs left in the ground also may be saved with the mulch.
Later in the early spring when your plants are budding out they can be vulnerable to a frost. The frost can kill those new buds, even on extremely hardy plants. Plant covers will be key in saving those buds for late winter early spring frosts.
In closing, be ready for the possible coming hard freezes. have your plant covers on hand, mulch the perennial beds, wrap the tree trunks and watch the weather reports. A little preparation can save many garden plants from unnecessary damage from a hard freeze, or a frost.