Agriculture Reference
In-Depth Information
tion. Agricultural specialists at provincial Ministry of Agriculture offices can
be good sources of information on climate as it relates to crop production in
a given area. In the United States, state and county Cooperative Extension
offices often have information on climate and fruit crop selection and pro-
duction.
Think long-term in choosing a site and crops. Orchard crops are very
long-lived. Depending on the crop, some trees and bushes can easily remain
productive for 75 years or more. In a commercial orchard, 15 to 20 years is a
good productive life expectancy, due more to shifting consumer preferences
than the productivity of the trees.
Winter Temperatures
Winter temperatures are the first factors to evaluate. Northern growers need
to consider the risk of freezing injury to tree trunks, branches, and buds from
late fall through early spring. Southern growers are concerned with the ac-
cumulation of chilling units, which temperate zone fruit trees need to meet
their dormancy requirements and develop new shoots, leaves, and fruit each
spring.
Temperate zone plants require a dormant or rest period during the
winter. Shorter days and cool night temperatures trigger the trees' entry into
dormancy. Physical and chemical changes take place in the buds, bark, and
wood that allow them to survive winter temperatures.
Once trees are dormant, they must spend a certain amount of time at
temperatures between about 32 and 55°F (0 and 13°C), during which time
chilling units accumulate. Chilling units accumulate most rapidly near 45°F
(8°C). Temperatures below 32°F (0°C) do not contribute to chilling, and tem-
peratures of 70°F (21°C) or more for as little as 4 hours can actually reverse
chilling that has already occurred. Without the necessary chilling, the trees
will be unable to bloom, leaf out, or grow normally.
Different varieties, even within the same crop, can have very different
chilling requirements. High-chilling apples, for example, require more than
about 800 hours of chilling; medium-chilling apples need 400 to 800 hours;
