The
late harsh frosts which blasted much of Australia's east coast
in early Spring had various effects on newly planted olive groves.
The coldest newly planted groves which have been reported to us
were in Queensland's Granite Belt which recorded three consecutive
mornings to minus 9 Celsius. There were a number of groves
planted with young trees which had only been in the ground 4 -
12 weeks through the winter and therefore hadn't grown much.
Damage
throughout North New South Wales and Queensland varied from
trees in a couple of orchards having 'tip-burn' and therefore
having to reshoot and start again, to groves which had very little
or no damage at all. The orchards all received the minus 8-9 degrees
Celsius mornings.
The
main factor which determined the amount of damage a grove
received was the availability of water. Those groves which
were not irrigated were the worst hit. Another interesting
factor is that the groves which had too much water were also badly
damaged. The explanation for this seemingly strange situation
follows.
If
you place a tray with 1 millimetre of water and another with
10 millimetres of water in the freezer at the same time, which
will freeze first? The 1 millimetre tray , due to its having
a thinner layer of water to freeze. It is the same in a
plants leaf. If the plant is not irrigated and therefore
is lacking water, then there is very little water in the leaves.
When the bad frost arrives, the water in the leaf freezes very
quickly. At the point of freezing, the water expands and
literally smashes the leaf and even stem tissue.
The
situation with overwatered trees works in exactly the same way.
Overwatering rots the roots of the tree and therefore
water cannot be taken from the soil through the roots (because
they are rotted off) to the leaves. The leaves are therefore low
in water just like the non-irrigated tree and the freezing process
is the same.
We
understand that there are a number of other factors involved
with the damage caused by extreme frosts, however, proper irrigation
techniques will reduce the damage significantly.
Rejuvenation
of Young Frost Damaged Trees
(Adapted
from the October 1995 Olives
Australia Newsletter)
A
number of enquiries have been coming in regarding the growth habits
of frost affected trees. The trees at our nursery are fully exposed
to frost throughout the winter months, however, severe frosts
like those received in many parts of Australia during early Spring
when a lot of soft, new growth had occurred, are entirely unpredictable.
If
you were unfortunate enough to have the severe frosts in
your area and if your young trees were effected, then the following
information will be of use.
If
the tip has been damaged to the point where it will not grow
again, then the tree will reshoot from live buds lower down the
stem. Allow these buds to shoot and grow into branches approximately
20cm (8") long. While these shoots are growing they
will be promoting root growth under the ground. When you finally
choose the most vigorous of these new shoots as the main trunk
for your tree, and remove the others, the roots which have been
building up will then cause your newly chosen trunk to really
take off.
Remember
to keep your plants irrigation at an optimum level, that is, not
too wet or too dry. This is the main key to reducing the effects
of extreme frosts.
Cold
Hardiness of Olives
(Adapted
from the October 1995 Olives
Australia Newsletter)
The
following brief notes are extracts from a 12 page Californian
paper titled, "Freeze damage and cold hardiness in olives:
findings from the 1990 freeze."
In
December 1990, California USA received a severe, fast hitting
freeze which brought temperatures down as low as minus 22.8
degrees Celsius (-9F), and temperatures remained below freezing
day and night for five days! It struck fast and the olive
trees weren't properly acclimatised to it. The different
olive varieties came through as follows:
Ascolano
and Mission were the hardiest. The mature trees were cut
to the ground at -20 Celsius but reshot in Spring.
Barouni
and Sevillano were killed at around -18 Celsius.
Arbequina,
Azapa, Kalamata, Picual, Salome and Verdale did not fare as well
as the previous varieties.
Manzanillo
and Nevadillo were worst hit in this devastating freeze.
Summing
up, all mature olives in good health will handle -10 Celsius
without any real stress. The 1990 California freeze situation
was a freak and may never be experienced in Australia.
