Classifying frost tolerant plants is really based on arbitrary
How heavy or
cold is the frost?
Is it -2°C or
down to -12°C.
In Australia we
don't really get the extreme cold of the upper northern hemisphere, so much of
their advice does not apply to our conditions.
We don't need to remove all water plants from the pond and store them
through Winter, because the pond freezes solid.
Other terms often
used, are frost hardy and frost resistant plants. Some plants go dormant during the cooler
months and in a way avoid the frost.
Plants like Japanese Irises produce better flowers if they get a few
good Winter frosts.
What causes frost?
occurs when the following 3 thing happen:
- The surface temperature must be at or below 0°C.
- The conditions must be calm, allowing the colder air to
sink and pool around low lying areas.
- The surface temperature must be sufficiently cool to
cool the air to below its dew point.
This is where the water vapour in the air is condensed into water (dew)
and then further cooled to freeze onto the surface.
Sunlight warms surfaces during
the day, but if the surfaces cannot retain sufficient warmth through the night,
the heat will dissipate into the cool clear evening skies. Both dew and frost
form after several hours of darkness. If
the temperature is about 0°C, dew will form. If the temperature falls below 0°C,
frost will form.
What are the effects on plants?
Many plants can be damaged or killed by
freezing temperatures or frost. This
will vary with the type of plant and tissue exposed to low temperatures. For many plants the damage is caused through
the water in the plant's cells freezing.
As the water freezes it expands and for some plants the sharp ice
crystals rupture and damage the cells and/or their contents.
Tender soft-tissued plants, such as Miniature
papyrus often die when exposed to frost. Frost tolerant plants,
like Baumea, tolerate lower temperatures. While some perennials, such as Lythrum and
Water Hibiscus can be classified as being frost
resistant plants, by becoming dormant after the first frosts and then
start to re-grow when the weather warms in Spring. Some plants may completely turn brown and drop
all of their leaves, leaving only the stems or stalks standing. Many evergreen
plants, such as the Tassel cord rush, will withstand frost although all or most
How can I reduce
- Choosing frost tolerant plants can
help to minimise the plant losses.
- Positioning your water feature so that
it is located in a warmer part of the garden or is more sheltered from the cold.
- Draping shade cloth over selected
plants can help to reduce the temperature drop around the plants and so reduce
the potential for freezing.
- Wind is a factor that is difficult to
control, but in some high value commercial crops they introduce large fans and
even helicopters to move the still air.
- At Oz Watergardens we run our
irrigation sprinklers over some areas of the nursery in order to reduce the
potential damage that a heavy frost may cause even to our frost tolerant plants.
simplify the listing of our frost tolerant
plants, we have decided to base it on our
experiences with the plants at our nursery.
We get about a dozen or more frosts each year and generally only down to
-3°C. The list is divided into three
- Evergreen plants that are able to
tolerate only a few light frosts ( around 0°C )
- Evergreen plants that are able to
tolerate more frequent frosts ( down to -3°C )
- Dormant plants. In our opinion, the dormant plants should be
able to tolerate heavier and more frequent frost and are therefore better
described as frost resistant plants.
- Prune the frost damaged foliage after the
frosty weather has finished. The
damaged parts still shelter or protect the plant parts lower down.
- For information on the plant care and maintenance,
go to our Tips & Hints page.
Please use our store locator to contact your nearest garden
centre, to place an order.