<table border=0 cellpadding=2 cellspacing="0"><tr><td>
<pre>The discussion about cold climates and olive trees has many facets
which we in Australia are in some ways only beginning to learn.
Recent winters have shown that measuring cold simply by a
`degrees
Celsius' temperature is helpful but not necessarily conclusive
when
selecting a site for olive growing.

The photo of the olive trees covered in snow in `Growing Olives
– An
Overview' by Olives Australia was taken in Tuscany, Italy. It is
not
unusual for this area to receive snow, and often in decent dumps like
in the photo where about 500mm fell over a couple of days. However,
the trees suffered from limb breakage and bruising. Some of the
varieties in that particular grove were the typical Tuscan Leccino,
Frantoio and Moraiolo.

Here in Australia I have seen baby olive plants (just 70mm tall in
pots) only receive minor leaf tip burn from temperatures of minus 5
Celsius in the nursery – but I have also seen two year old trees
(2
metres tall) nearly killed by a few minus 3 Celsius mornings in a
grove. Why the difference?

There are a number of factors, some of which are:

1. Plant and soil moisture levels – A tree which is dry in its
leaves
and wood is much more susceptible to frost damage than a tree which
has sufficient moisture levels. There are simple laws of physics
which support this. NB. A tree may be dry in its foliage because it
is too wet at its roots – the roots may be rotting and therefore
unable to draw water up to the foliage. Also, if the irrigation
water is too salty, the tree roots will reject it and while plenty of
litres are being pumped onto the tree, it may not be drawing it up to
the foliage.

2. Freezing and thawing speeds – A critical factor is the speed
at
which the cold air arrives in the grove and the speed at which
thawing takes place in the frozen bark or leaves. If a tree has a
frozen layer of bark just before sunrise and the sun rises in full
glory to shine (and heat) the eastern side of the trunk, the fast
thawing of the frozen cells can cause `cell bursting' and
tissue
damage. This is a key reason for the majority of frost-split bark to
be found on the eastern side of the tree. I'm not sure whether
the
following experience is a rule across all groves or not but I have
been in groves where the trees growing on an eastern slope (facing
the rising sun) have bad trunk splitting from fast thawing and those
on the western slopes have very little if any damage at all.

3. General tree health – As with humans, olive trees are better
able
to fight off cold, heat, disease, physical damage and pests when they
are in good health. This good health is obtained through a regular
system of irrigation, pruning, fertilising and pest control within
the grove.

Due to the many factors and variations from region to region I
personally think the best advice any grower can get about cold
tolerance is from other local farmers. If they do not grow olives,
see if you can find a grower with another evergreen tree crop, which
keeps its foliage through the winter.

When selecting a variety for a `cold' area try to ascertain
what `very cold tolerant', `medium cold tolerant' and
`susceptible to
cold' actually mean. A variety recommended as `susceptible
to cold'
by an author writing from Tuscany (where temperatures can drop to
minus 15 Celsius and more) may in fact be quite `cold
tolerant' for
climates which drop to minus 8 Celsius.

Whatever the case, once the trees are in the ground keep their
moisture levels right and ensure their health.

Kind regards,
Julian Archer
Olives Australia
</pre>
</td></tr></table>