Choosing the right fruit trees for your
orchard or garden has a big impact on how they will grow. How you
care for them is very important, but if you start with the wrong tree
for your climate, then you could spend a lot of time and money for
very little gain. Our Blog this week reveals some key climate related
issues to consider when selecting your fruit trees.
You will find that you can plant fruit
tree crops in very diverse climates and generally they will grow, but
if the climate is not ideal for the fruit tree cultivar you are
working with, then it will not be as productive as it should be, be
more subject to pests and diseases and ultimately may die
prematurely. Healthy, well cared for fruit trees in the right climate
can last for a very long time and produce beautiful crops every year.
Let's start with some basics. Fruit
tree crops are, for example, apples, oranges and mandarins, whereas
fruit tree cultivars of these crops are, for example, Golden
delicious apple, or Valencia orange. There are large numbers of
cultivars for fruit tree crops., especially the crops that are very
commonly grown and consumed. Some cultivars are very old and others
are newly developed by fruit tree breeders.
Issue 1 - What are all the fruit
tree crops and their cultivars that you could select, as your local
nursery or even fruit tree breeder may not have the actual potential
range you could choose from? They will normally sell what they have
unless you ask them for something else.
Different fruit tree crops have
different sensitivity to climate, for example, oranges and mandarins
can grow in a diverse range of climates from cool temperate to sub
tropical. Whereas bananas like the warmer temperatures of sub
tropical and tropical regions and cherries prefer more temperate
Cultivars of fruit tree crops are
generally climate sensitive as well, for example, most apple
cultivars prefer more temperate climate, but a small number can grow
in sub tropical cilimates. Whereas a cultivar like Valencia orange
can grow in a diverse range of climates.
Issue 2 - What is the climate
profile of all the fruit trees you are interested in and are there
cultivars of those fruit trees that suit your climate?
In Australia, there are general climate
zones of cool temperate, temperate, warm temperate, cool sub
tropical, sub tropical, warm sub tropical, tropical, arid and
mediterraneum. Not all fruit tree sellers will use these zones, they
may just say, temperate, sub tropical and tropical. You may or may
not know your climate zone and such zones are often problemmatic as
they cover such broad areas and tend to generalise of lot of
different climates. In addition, you may have created a micro-climate
on your property where the location of your fruit trees is warmer
than the prevailing climate.
Issue 3 – What is the local
climate profile of your garden or orchard and have you created a
micro-climate? Without knowing this, you have no objective way of
choosing the right fruit tree
Gardeners familiar with buying fruit
trees may be aware of the term high chill or low chill cultivars.
Where I live in Brisbane, a sub tropical climate, gardeners may look
for a low chill variety of an apple or a peach, whereas a person
living in a mountainous part of Tasmania would look for a high chill
Issue 4 – What does chill profile
mean, how is it calculated and is it relevant for all fruit trees?
The amount of time that a fruit tree
experiences chilling is important for its floweriring process which
leads to timely fruit set. This is particularly the case with many
varietes of pome fruits, stone fruits, nuts and berries. Yet some
fruit trees don't care about chilling, such as the ones growing in
There are two methods of calculating
fruit tree chill profile. These are:
(a) Chilling hours – This is the
total number of hours in a year where the air temperature is below
7c. It is very difficult to get this type climate information from
your weather bureau, farmers may use temperature measuring devices to
collate this information.
(b) Chilling units – This is a
measure developed in Australia and is being adopted in a number of
countries of the world. It uses the lowest mean temperature in a
month of the year, then compares this temperature to a chilling unit
scale, for example, in my home town of Brisbane, the lowest mean
temperature is in July and its 15 C and this equates to around 190
chill units (low chill). When you reach a lowest mean of 19c, then
chill units are 0 and this would be a tropical climate, whereas an
average 6c for Orange in NSW would be 1100 chill units (high chill) .
Issue 4 – Is it possible to be
exact with a chilling unit figure on a fruit tree and who generally
Most chill unit figures are quoted as
ranges, some crops have very broad ranges, for example a Valencia
orange can grow from low to high chill, whereas with Apples, very few
will grow in low chill below 250, but nearly all cultivars will grow
fine from 300-1000 chill units. The ranges are most often provided
by the fruit tree breeders, that's if they use chill units. They may
instead completely ignore chill factors and use zones and say, for
example, this cultivar is suitable for sub tropical only.
Issue 5 – If you use chill units
as a measure, how do you know what your chill unit profile is so that
it can be matched against the fruit tree cultivar.
For most gardeners, this is a stab in
the dark as they would not know how to calculate their chill units or
they may use chill hours instead of units and the hours, as mentioned
previously are nearly impossible to calculate unless you have a
device to track temperatures 24/7 for every day of the year and do
this over a number of years.
Issue 6 – Where does this leave
you as a gardener attempting to make objective decisions?
It leaves you in a very tricky
situation. For persistent gardeners it will take a lot of time to get
the bottom of these questions. This is impacted by the complexity of
the impacts, the information is located in many places and often has
its own particular bias. You could join a local fruit tree growing
club. This should be a storehouse of local knowledge, depending on
how well it is run.
How does our web site solve these
issues for fruit tree gardeners?
(a) We store the climate profile of the
40 most common fruit tree crops with over 700 cultivars of these
crops covering all climate zones of Australia. These profiles have
been converted into chill unit ranges for all fruit tree cultivars
(cultivars for tropical climates will have very low or zero chill
factors). We are progressively adding more fruit tree crops and
cultivars. We do not sell fruit trees and will list cultivars from
any breeder, thus giving you a very broad picture of the potential
crops to choose from.
(b) We store local climate information
in our web site and when you choose your nearest weather station for
your orchard, the web site creates a chill unit profile for your
garden and can be further tuned for your micro climates.
(c) When you search a fruit tree for
your climate, all the cultivars will be listed which match your chill
profile and that of the fruit tree. Where our web site logic finds
that your chill unit profile sits within 20% plus or minus the mid
point of the cultivar chill unit range, the cultivar is marked as
Ideal to plant and outside this mid point range as OK.
(d) You can then easily access the
fruit tree breeders against each cultivar (Australia only at present)
and contact them directly or ask your local nursery to buy from them
on your behalf.
The search is very simple to use and
will also show you whether the cultivar is an early, mid or late
cropping variety, so if you were planting oranges and wanted to
extend your cropping season, it would be best to have three trees
which were early, mid and late varities. The search also shows dwarf
varieties which is very userful if you do not have much space.
You can see how it works by clicking
here. Based on our research, this fruit tree search is the first of
its kind in the world.
Peter Kearney, www.cityfoodgrowers.com.au